Hot trip from FL to IL

[Mark Rinker]

Temps were 90+ degrees and the humidity felt about the same, with high of 98F in FL. Temps didn't drop below 90F until middle of Illinois...

Noticed that the water temp fluctuated alot, waiting for the fan clutch to engage - which seems about 20 degrees too late. This is the first time that I have seen this truck go into this pattern, and repeat itself over and over - it clearly had more to do with the outside temps than the load behind the truck, which was not a big boat. I was running a +40hp tow tune. Temps never got to a point where I felt the need to return to stock. Never heard engine rattle or knock, even when the gauges were not pretty to look at, climbing up Monteagle near Chattenooga, TN.

Each morning, I'd carefully watch the progression of fluid, ambient (outside) and IAT temps, and the pattern of what happens is very clear and predictable.

Engine come up to temp first, thermostat controlled and settles in at around 190.
Tranny temp comes up slower, but soon matches water temp (not suprisingly as they are coupled for cooling purposes).
At the first grade, or excessive use of the right foot, the water temp in this heat and with 15K load will rise to 220-230 degrees, before the fan clutch engages and pulls the water temps back into the 200-210 range.
First problem now occurs, as 18qts of trans fluid has now matched the peak water temperature of 230 degrees. It may now take hours for the fluid to return to under 200 degrees - in fact my recent experience is the fluid never dropped under 220 for the rest of the day.
Who knows what was going on with oil temps during all of this. You can bet there is wide variations - the LBZ turbo, when overworked, dumps alot of heat into the oil, that is seen by the operator as water temperature increases. The key to see when this is happening is when the ambient air temperature and the IAT temperature begin to diverge, with a spread over 30F. When they get over 50F apart, the heat soak will happen 100% of the time.So anyway I ran about 62mph in whatever gear (5th or 6th) the Allison would hold for three twelve hour days, covering 1800+ miles, with average EGTs in the 1150-1250 range, peaks of over 1400 pulling hills, and would say average water/trans temps were 220-225 - until midway through IL when ambient temps dropped in the 70s/80s, and water/tranny temps moderated about 10F each.

Oil change interval will be shortened - this stuff is coming out today. Tranny fluid will get a 7qt drain and fill, new spin on filter today as well.

On my mind:

Bigger/more efficient turbo might well fix the entire problem, as that is where the heat cycle starts, dumping heat into the oil and into the intake charge;
Bigger radiator might also be just as effective, by dissipating the heat faster from the engine coolant;
LB7 fan clutch swap would be the the most cost effective, and quickest/easiest place to start - i.e. couldn't hurt;
Additional oil and/or trans fluid cooling might help the gauges look better, but the oil is still getting beat to death by the turbo...You southern state guys (anywhere with ambient temps >85F) that experience the LBZ heat soak while towing should, IMO

Careful towing with additional fuel rates; if you see heat soak, return to stock and compare results
Keep the cooling stack clean
Consider fan clutch update, and/or additional oil/trans fluid cooling

[DmaxMaverick]

I think you are attributing too much blame on the turbo. It will soak heat, and dump it into the engine, to some degree. The actual turbo oil flow volume and oil-heat exchange is very low, by comparison, and likely adds little, if any, noticeable temp increase to the entire oil volume. A more likely suspect is the coolant-heat exchange. Duramax turbos are coolant-cooled. However, the flow volume is very low.

If you are having fan clutch engagement issues, you have two possibilities. The clutch is failing/failed, and needs replacement; one or both thermostats are not operating properly. Only one component "decides" when the fan clutch engages (assuming the clutch is healthy). The thermostat(s). Hot engine coolant passing through the radiator increases the air temp passed to the clutch. Using A/C usually advances the clutch engagement, only because the air temp begins higher, meaning less engine coolant heat is required to attain the same temp seen at the clutch, however, it is rather minimal compared to the heat transfer of engine coolant with fully open thermostats. The CAC (charge air cooler) will have a greater effect, under heavy(ier) engine loading. The effect(s) are cumulative, and exponential, meaning, a snowball effect. In the case of LLY and LBZ (and 2002+ CA LB7's), the EGR also adds heat into the coolant (which is the concept, afterall, with less heat retained by the exhaust), although minimal under loading, as the EGR is inactive at this time. The EGR is coolant-cooled, with a greater coolant exposure area within the head (compared to non-EGR engines), offering the opportunity for greater heat transfer from the head to the coolant. It is possible that later model cooling systems are closer to the capacity threshold than earlier models, leaving a system more sensitive to heat transfer changes, and ultimate capacity. JK's comment on the late model fan operation changes are probably right on with this. Creature comfort: Less noisy/active fan operation. I recall numerous comments on TDP in regards to this beginning with the late LB7 and early (2004) LLY, with complaints ranging from "too noisy", to "on and off too much". I think the 2005 model "overheat complaints" are a direct result of this. A noisy fan is a happy fan (and engine). Add to the whole picture, low(er) cruising speed engine RPM's, less efficient fans (less noisy), and added cooling system components, and you have a recipe for a greater cooling system performance and capacity needs.

[Mark Rinker]

Interesting stuff - thanks for the input, DMax. In this case, I am like the race driver that pulls into the pits and says, "...its pushing and has a miss in 4th gear WOT", but don't claim to know the answers why!

One observation that led me to the turbo leading the heat soak is the ambient temp vs. IAT spread, outlined above. In Minnesota, its hard to get a 50F spread. In southern states summertime 90+F, its easy...

It would be interesting to be able to swap a few aftermarket turbos on and off the LBZ, tow under controlled circumstances, and see how much of the soak is turbo induced, and how much is simply block heat from combustion...

Who has an early LB7 fan clutch they'd like to sell?

[DmaxMaverick]

The ambient air temp does have an effect on the whole ECT picture. Every component exposed to the air will have a more narrow delta T (the temp spread between the beginning temp, and the controlled/attempted temp) as the ambient temp increases. Ambient air temps play several parts in the equation. Heat is an absolute, the same as counting eggs in a basket. It cannot be removed, only "moved", from one medium to another.

The oil pans, engine and tranny, are cooling components. As the ambient temp increases, the air's ability to carry away heat from these surfaces decreases. The "turbo pursuit", I think, will have little to no effect. Some are more efficient within specific ranges, and may offer some changes within those ranges. But, it's always a trade. A turbo is a turbo is a turbo. They all do exactly the same thing. The only difference is the range and volume in which they do it (housing and AR values).

Trying the LB7 fan clutch may be the answer to your issue, as long as there are no other underlying issues. From my observations (no scientific data on this), earlier clutches are more aggressive, and seem to have a closer drive ratio (less RPM loss through the viscous coupling). Pulley size could play a part, but I haven't measured them.

You may also get a closer look at the thermostats. Temp swings should be smooth and essentially normalized. If not, you could have a sticky stat(s). This is usually indicated by ECT swings between extremes.

[JohnC]

Forget about the air temps. If there's a problem it's on the end with the 1400 degree exhaust gasses running through it...

[Mark Rinker]

Is there any room unused to build a custom radiator of the same dimensions, but slightly thicker? I know a custom radiator builder that can do anything - just bring your checkbook...

Also, someone from TDP moved the trans cooler from in front of the stack. Would that make sense?

[DmaxMaverick]

Every little bit helps, BUT........

You are heading toward covering an underlying problem. These problems tend to lay low, hide under "patches", then blow, catastrophically. If this is the first time you've noticed this trend (I don't recall you posting about it before), that means it was fine before, and something changed to cause the issue. Beefing up the cooling system may reduce your symptoms. Enough to let the underlying problem build to the point of no return.

Cooling system improvements are not discouraged, by any means. However, to do it right (and especially for commercial use), it must be healthy to start with, or you must at least identify the original problem and correct it.

There are thousands of these trucks on the road. Many of them do what you do, and more, with no similar issues typical for the model year. I camp with several folks with them (2006 is a very popular model year), and none of them tow light (at or above GCWR), some with monster tires/lifts and power. CA summer towing is the test.

[Mark Rinker]

Understood. I will probably replace the thermostats as good measure - but don't think they are malfunctioning.

What changed was the ambient temps of >90. I never was knocking, steaming, coolant puking hot, just observed the cycle that many have seen, without altitude, big power tune, or an overly large load. Once outside temps moderated, the heat soak cycle disappeared.

If I'd been running the stock tune, pretty sure temps would have been kept under control - i.e. never exceeding 200-210 range.

What I would like to do is apply the best mods to be able to run a +40 tune for the driveability and loaded mileage benefits, and see more normal temps, even in some southern heat.

Maybe I am expecting too much, but love the challenge of finding the weakest link, and improving it!

[JohnC]

What you noticed may be perfectly normal. As ambient temps increase, the ability of the cooling system to shed heat is reduced. Where you may have been fine before, now something has to change. As the radiator temp increases, the difference between the radiator temp and the ambient air increases as does the ability to shed heat. If the fan clutch didn't kick in the temp would rise until the difference in temps was roughly what it is under what you're calling "normal".

The thing that's probably the most concern is the trans temp. Probably an air to air cooler plumbed after the water jacket cooler would cure that, but in the winter you'd probably want to bypass that (nothing a thermostat wouldn't cure!) OTOH, synthetic trans fluid is fine at those temps.

[dually2002]

Temps were 90+ degrees and the humidity felt about the same, with high of 98F in FL. Temps didn't drop below 90F until middle of Illinois...

Noticed that the water temp fluctuated alot, waiting for the fan clutch to engage - which seems about 20 degrees too late. This is the first time that I have seen this truck go into this pattern, and repeat itself over and over - it clearly had more to do with the outside temps than the load behind the truck, which was not a big boat. I was running a +40hp tow tune. Temps never got to a point where I felt the need to return to stock. Never heard engine rattle or knock, even when the gauges were not pretty to look at, climbing up Monteagle near Chattenooga, TN.

Each morning, I'd carefully watch the progression of fluid, ambient (outside) and IAT temps, and the pattern of what happens is very clear and predictable.

Engine come up to temp first, thermostat controlled and settles in at around 190.
Tranny temp comes up slower, but soon matches water temp (not suprisingly as they are coupled for cooling purposes).
At the first grade, or excessive use of the right foot, the water temp in this heat and with 15K load will rise to 220-230 degrees, before the fan clutch engages and pulls the water temps back into the 200-210 range.
First problem now occurs, as 18qts of trans fluid has now matched the peak water temperature of 230 degrees. It may now take hours for the fluid to return to under 200 degrees - in fact my recent experience is the fluid never dropped under 220 for the rest of the day.
Who knows what was going on with oil temps during all of this. You can bet there is wide variations - the LBZ turbo, when overworked, dumps alot of heat into the oil, that is seen by the operator as water temperature increases. The key to see when this is happening is when the ambient air temperature and the IAT temperature begin to diverge, with a spread over 30F. When they get over 50F apart, the heat soak will happen 100% of the time.So anyway I ran about 62mph in whatever gear (5th or 6th) the Allison would hold for three twelve hour days, covering 1800+ miles, with average EGTs in the 1150-1250 range, peaks of over 1400 pulling hills, and would say average water/trans temps were 220-225 - until midway through IL when ambient temps dropped in the 70s/80s, and water/tranny temps moderated about 10F each.

Oil change interval will be shortened - this stuff is coming out today. Tranny fluid will get a 7qt drain and fill, new spin on filter today as well.

On my mind:

Bigger/more efficient turbo might well fix the entire problem, as that is where the heat cycle starts, dumping heat into the oil and into the intake charge;
Bigger radiator might also be just as effective, by dissipating the heat faster from the engine coolant;
LB7 fan clutch swap would be the the most cost effective, and quickest/easiest place to start - i.e. couldn't hurt;
Additional oil and/or trans fluid cooling might help the gauges look better, but the oil is still getting beat to death by the turbo...You southern state guys (anywhere with ambient temps >85F) that experience the LBZ heat soak while towing should, IMO

Careful towing with additional fuel rates; if you see heat soak, return to stock and compare results
Keep the cooling stack clean
Consider fan clutch update, and/or additional oil/trans fluid cooling

MY engine temps don't go over the 190 mark (empty) until the ambient temp gets about 85 or better.When towing fifth wheel in 90 plus temps the engine temp gets to about 215 before the clutch kicks in and brings the temp back down to the 195-200 range in short order unless I am pulling a hill.The trans temp gets to about 210-215 and stays there unless I encounter a hard pull. The only time my fan kicks in (empty) is in traffic and temps 95 or better. The thermostats may be someting to look at. I am running a Kennedy 50-100 hp tune with 4 inch exhaust. Haven't used the 100 hp tune while towing cause I don't need it. The 4 inch exhaust might help in reducing overall engine heat

[Mark Rinker]

Thanks - sounds similar to the results I had with my '01 and '02 LB7 trucks, running JKs tunes.

I miss them...

[DmaxMaverick]

If your fan clutch engages, and does so otherwise normally (regardless of the actual gage temp), there's no reason to suspect it. If you are changing stats, they will determine the fan engagement temp. Want the fan on earlier (lower temp)? Go to a lower temp stat. The fan clutch is passive. In the absence of hot coolant going through the radiator (stat(s) open), it sleeps.

The later clutches may be more "lazy" than earlier, and that can delay the process. But only in the sense that once it begins to engage, until it is fully engaged. If your issue is a hard temp limit of engagement (the temp it engages, and disengages), the clutch isn't the issue.

In any case, I don't suggest replacing both at the same time. Even if it does remedy the problem, you'll never know the cause (and toss perfectly good -and expensive- parts).

[dually2002]

If your fan clutch engages, and does so otherwise normally (regardless of the actual gage temp), there's no reason to suspect it. If you are changing stats, they will determine the fan engagement temp. Want the fan on earlier (lower temp)? Go to a lower temp stat. The fan clutch is passive. In the absence of hot coolant going through the radiator (stat(s) open), it sleeps.

The later clutches may be more "lazy" than earlier, and that can delay the process. But only in the sense that once it begins to engage, until it is fully engaged. If your issue is a hard temp limit of engagement (the temp it engages, and disengages), the clutch isn't the issue.

In any case, I don't suggest replacing both at the same time. Even if it does remedy the problem, you'll never know the cause (and toss perfectly good -and expensive- parts).

I assume D-Max fan clutches are different in that they are not viscous clutches the are calibrated to engage at a calibrated temperature by the means of a thermostat coil on the radiator side?

[DmaxMaverick]

I assume D-Max fan clutches are different in that they are not viscous clutches the are calibrated to engage at a calibrated temperature by the means of a thermostat coil on the radiator side?

As with all HD fan clutches used on light trucks for about the last 30 years, it's a viscous coupler with thermostatic positive engagement. Nothing new here.

[richp]

Hi,

My fan clutch occasionally engages on a cold start, and roars at me for the first couple of miles.

The dealer says this is a normal condition, but it doesn't seem right to me.

Any thoughts on that?

[Mark Rinker]

>>> Want the fan on earlier (lower temp)? Go to a lower temp stat. The fan clutch is passive. In the absence of hot coolant going through the radiator (stat(s) open), it sleeps. >>>



I am following you, but am trying to influence the fan clutch to engage earlier, around 210-215, rather than 225-230 water temps.

The clutch may be passive, but it still has a preset threshold of engagement...my concerns are:


Why change OEM engine operating parameters to reach that threshold earlier?
What negative affect might changing to lower temp stats have on ECM based engine temperature assumptions in programming?Change the stats, you change your cylinder head temps. Not sure living in MN that I want that - to solve an infrequent summertime FL/TX problem?

[Mark Rinker]

Hi,

My fan clutch occasionally engages on a cold start, and roars at me for the first couple of miles.

The dealer says this is a normal condition, but it doesn't seem right to me.

Any thoughts on that?


Mine sometimes do this as well. I think its 'normal', but not consistent at all.

[DmaxMaverick]

Hi,

My fan clutch occasionally engages on a cold start, and roars at me for the first couple of miles.

The dealer says this is a normal condition, but it doesn't seem right to me.

Any thoughts on that?

Absolutely normal. Viscous coupler fan clutches have been doing this since day one. Some more than others. As the engine sits, cooling off, so does the clutch, and the silicone fluid inside it. The fluid settles, and becomes thicker as it cools. On a cold start, it will take a period of time to circulate the fluid evenly, and warm up so it is distributed evenly. The result is an engaged fan during this time. Why some do it more/less than others under the same conditions, that's still a mystery. The internal configuration is not symmetrical, so perhaps it's the clock position when it stops is the cause (fluid settling in different proportions/areas), but I'm only guessing.

[DmaxMaverick]

I am following you, but am trying to influence the fan clutch to engage earlier, around 210-215, rather than 225-230 water temps.

The clutch may be passive, but it still has a preset threshold of engagement...my concerns are:

Why change OEM engine operating parameters to reach that threshold earlier?
What negative affect might changing to lower temp stats have on ECM based engine temperature assumptions in programming?Change the stats, you change your cylinder head temps. Not sure living in MN that I want that - to solve an infrequent summertime FL/TX problem?

I don't know, Mark. I don't have any hard data on the clutch engagement map, only observations (and GM doesn't make available this info). It could be your stats are tired, defective, or fouled in some manner. If they don't operate smoothly, the result will be wild temp swings. I don't know what was changed between the newer/older fan clutches. Often, GM changes part numbers for no functional reason at all, so it's hard to say what is the difference. There's no visual difference between the two clutches that I can see.

You may be right in replacing the clutch and stats, or just the clutch, and I wouldn't be surprised at all if it's necessary to cure your issue. I'm only suggesting a course to better diagnose the root of the problem, and possibly save some time/money.

The fan clutch engagement temperature is always well below that of the thermostat temp. The range is usually in the 120-150° range, historically. The differences are greater in the area of engagement rate (range between beginning and full engagement), and percentage of coupler efficiency (effective ratio), which is also non-disclosed information. In operation, they are not unlike a torque converter (which is also a viscous coupler). The coolant temp isn't a perfect exchange of heat between the radiator and clutch, as the efficiency of the heat exchange method is very low. A coolant temp of 240° may only be an actual air temp at the clutch of 180° (a SWAG, for the sake of argument).

[moss6]

Love/Hate this subject having spent so much time on it myself; continues to be very interesting though each time it is discussed especially when intelligent discussion is there.
Duramaxmaverick's second post still leaves me scratching my head a bit though even after a couple of readings; that is in regards to the delta t. Delta t between the ambient and the intact temps in my experience is all over the spectrum. I've seen 15 degrees with light load with ambients in the 80's and around 90 degrees with the same ambient and heavy load, that delta t is near 100% turbo heat load and when high in my experience the start of a chain of heating events that effects all cooled systems that don't back off until the load is lessened or the fan clutch kicks in at about 232 degrees on the LBZ. At 232 degrees the clutch does start cooling the water back down relatively quickly but at that point the trans and engine oil are at a point that it takes a long time to recover. If you soon afterwards have another heat event then the oil temps become even higher and the likelyhood of a third, forth and so on event become more likely unless you decrease the load. Probably I just did not understand what the point was, I'm bad about that.
A 215 degree clutch might be better for keeping things more under control but I think it would really run alot without some other modification help, or maybe a lighter foot.
Some of you know what I did that took care of everything, I love the results. Now whether my fixes are just hiding a problem; I cannot say that I am 100% certain. What I can say is that since the modifications, I have put a lot of hard towing miles on the truck, I have had zero problems, and all temperatures are at near unloaded levels even when towing heavy and running a Kennedy tow tune. Turbo heat load is still around but better kept under wraps; it would be very nice if there was a good fix, I really think Ford putting the intercooler at the front of the stack is an excellent idea and could be done on the Duramax but would be a real chore.
Randy

[Mark Rinker]

The chain of events as you describe, right down the temps, are identical to what was my experience on this last return trip from FL to IL, where ambient temps declined and things returned to a more normal cycle.

Without oil temperature data, its hard to know where the heat load is accumulating, oil appearred thin based on oil pressure readings.

Hey...your mods work. If they are a band-aid, well, at least the bleeding has stopped! :D

I don't live and tow often enough in those southern temps to merit the effort/cost on the back-end, but am curious to see if there is another, more simple way to solve it on the front-end. If I have to listen to a fan clutch cycle on and off all day, under these occasional hot and heavy hauls, then so be it!

Another idea: How about pre-turbo water/methanol injection under these hot conditions to reduce the delta between ambient and IAT charge temps?

[Mark Rinker]

Moss6: Have you towed heavy, with your mods, in any high altitude situations?

[moss6]

First of all, I really hope DuramaxMaster stays involved in this thread as he offers some great insights on the subject that are a breath of fresh air to the resistance that is normally encountered when the subject of LBZ heat issues are discussed; especially so when brought up a year or so ago when I was heavy into addressing and fixing what I deemed to be a problem based on my experiences when towing heavy and wanting to upgrade to a point that I no longer had to worry about temps that were above what I considered 'normal' parameters.
I guess bottom line with me on this topic is that we can make the stock Duramax a far better towing machine than what we purchase from the factory. Stock it far outperforms any thing else that is available, and lets hope that Obama's plan for our auto industry does not lead to the total demise of GM and it's many superior products as compared to the rest of the industry.
Mark, with the engine oil cooler I added, the oil temps, even under the most extreme conditions have never exceeded 247 degrees, far below the high limits for oil degradation especially when using Delvac. I would love to see some oil temps with only the OEM cooler.
Since the addition of the larger trans. oil cooler I have never seen temps rise over normal unloaded levels.
Fan clutch engagement is pretty much non existant other than in a slow traffic condition after a hard tow and immediantly coming into a intown traffic situation. So I don't have to deal with that as a power robbing heat event scenerio as I did with the stock configuration.
I think that wherever you live if you tow heavy and push it a bit some additional cooling aides are an imeasurable benefit to the truck and more importantantly to your mental state if you love your truck as I do.

[moss6]

Lots of miles in the mountains of NM and Colo where we normally go pulling the fifth; and the very reason (along with bucking a strong wind anywhere) that I decided that I'd like to give the truck some cooling help.

Raton Pass NM/Colo 7834 feet, a good hard pull especially going South.
Slumgullion Pass Colo 11530 feet, very tough going South with all the sharp curves no way to maintain speed, max grades.
La Veta Pass Colo 9413 feet, good tough pull going west and always seems to be a strong wind against you.
Wolf Creek Pass Colo 10857 feet and some 7 to 8%, toughest going north, long twisty speed killer, along with Slumgullion not fun up or down.
Holman to Tres Ritos NM going north, twisty but good pull that lets you build some speed back in a few areas.

Any of those you will remember if you are towing heavy.

[Mark Rinker]

Interesting.

When towing oversize boats, I try to avoid routes with overly mountainous or twisty terrain, for obvious reasons. Also, there isn't much 'big water' in the mountains, but our destinations sometimes take us through them. My most common mountainous route is through Kentucky and Tennessee's 'bumps' (I24-I75) on the way to Florida. Montana, Idaho, and Washington state (I94-I90) west on the way to Seattle, BC's Rockies occasionally, New Mexico's (I40) southern route to Phoenix/Vegas/SanDiego or Nebraska/Wyoming (I80) route west to Salt Lake, instead of (I70) through Colorado Rockies...

With the K3500, trailer, boat, gear I am usually just under the 26K# cutoff for apportioned fuel/trip permits. With the Kodiak, was well north of 30K GCVW many times. I like boats that are around 12K, then the trailer/boat comes in around 15K with 8K of truck, gear, fuel. These boats also are <12' beam (width) so you can travel without cost and coordination hassles of rear escort cars, and generally will load out around 14' tall. I don't like going down the road taller than 14'4", too many ways to get in trouble. Wide is easy, tall is stressful.

What is your GCVW with gear, fluids, people aboard? Any signs of transmission slippage or burnt/stinky fluid?