cooling questions & options?

[bikinjoe]

Hello all,

I have a 1997 GMC with the 6.5 in it. I am towing a 30' fith wheel at about 12k. I done some air mods, 4" exhaust, replaced the radiator, and moved the pmd.

My problem is the truck overheats really bad anytime we go up hill when hauling. Not just 10-20 degrees, more like 190 to 230 or more a couple times.

At 2500 rpm it has plenty of power but the temp goes through the roof. At 2000 rpm or less I can keep the temp down around 210 but it feels very sluggish and just keeps loosing speed.

After many searches, a couple of the Diesel Page books and a phone call to John Kennedy it sounds like I should change the fan clutch to one of the HD style ones from Kennedy.

I don't have a problem doing that if it works. John gave me good information and I trust him. Though he said that I could have an underlying problem that the fan clutch change may not solve.

Like I said I have searched the forums and found a lot of information but am still a little confused. So thanks for any help that can be offered.

My questions are:

1) Is what I am describing normal for towing?
2) Has anyone had the same thing going on?
3) and by changing the Fan Clutch it solved the problem?
4) What is acceptable for the tempature when towing?

Any other suggestions, options?

I like this truck, it is paid off and does the job great. The problem is I don't want to end up on the side of the road with a dead truck in the middle of Eastern Oregon's desert.

Thank you, Richard

[JeepSJ]

Manual or automatic? If auto, is the TC staying locked?

When was the last time you cleaned the dirt/bugs/etc out of the front of the AC condensor?

Are you monitoring EGT? If so, what is your EGT on those hills?

The Kennedy fan clutch is nice, and if you put in a Duramax fan at the same time it will move some serious air through your radiator.

Use the search function - this topic has been discussed many times.

[KallyI]

1) Is what I am describing normal for towing?
That is normal for our trucks. Not acceptable, but normal.

2) Has anyone had the same thing going on?
Yes, check my signature for what I haul.

3) and by changing the Fan Clutch it solved the problem?
Can't help you on this one. I still have the original fan/clutch combo.

4) What is acceptable for the tempature when towing
My belief is that your engine should run at near normal temperatures, with the fan cutting in and out.

Any other suggestions, options?
I installed an intercooler, to cool the intake air down after the turbocharger, and now I am able to go up most hills without losing speed, and the coolant temperature stays below 220

[Hubert]

Clean the oil/ATF? cooler(s) and whole stack as mentioned above. Do you have the "skid plate" still? If you want to try adding a front spoiler under the bumper to help air flow go through the stack. It is suppose to help not sure it will solve any bad problems but again its suppose to help a little. What are the boost and EGT's. How is the smoke?

[Robyn]

Be sure you have the "factory" T stat in the little beast.
Once you get to around 215F the fan in that thing should be howling like its going to suck the radiator right on through.
If the fan clutch has a buttload of miles on it or you can see any signs that the viscous fluid is leaking from the clutch a fresh one is in order.
Many times the clutch will leak right around the bimetal spring on the front and then this oil collects dirt and this will slow down or stop the spring from reacting to the heat and then your clutch does not work right.

If your air flow is not compromised by bugs, leaves or such other junk up front between the AC condenser and the radiator then replace the T stat with a new factory (DELCO) unit.

If the fan is not howling like a tornado up there when things are hot then see John Kennedy for a fresh clutch.

Now if you get things all said and done and things still seem a bit warm try installing a direct reading aftermarket temp gauge into the head in place of the stock electric one.
The factory gauges have habit of being eroneous at times.

The factory gauges are kewl looking guess meters and thats it.

You want real time numbers then you need a burbon tube direct reading gauge to get it.

Any small anomaly with the electrical system in these trucks can make the gauges give a wide range of readings.

I have talked to several folks whos 6.5's run at 250F by the factory gauge when towing on a hot day under a hard pull.

If this was the case I believe all these engines would have seen major failures.

One couple in particular have a 96 with 300K on the clock and they have pulled their 32 Ft 5th wheel all over creation and the High temp reading has been a norm since the thing was new.

I am suspect of the gauges acuracy.

Just be sure your cooling system is healthy though.

In looking at your post about the temps???

190 is normal and 230 will not hurt things as long as its not for extended periods.

If you are only seeing 230f on the factory gauge I would install a manual gauge and see how that stacks up.

A very small error in the eletric gauge could be the only real issue.

BUTTTTTTTT the Kennedy clutch is a great investment for your rig no matter what else you do.

Hope this helps

Robyn

[bikinjoe]

Thanks for helping me out on this, trust me I've been doing the search and have found most of the answers.

It is an Auto, and as far as I can tell the TC is staying locked.

When I changed the radiator out I cleaned the bugs out of everything, that was about 1 month ago.

Not monitoring the EGT's, how neccesary is that?

How do the gauges help you exactly? don't they just tell you what is not suppose to be happening? or do they actually do something about it? I'm kind of lost here :)

I don't hear the fan screaming along, but over the diesel engine noise and exhaust how loud would it be?

The truck has 150k on it, and I just changed out the oil and trans fluid with Sythetic and both filters. I have done that pretty close to 3500-4000 miles for the past 20k that I have had the truck.

It sounds to me like a new factory T-Stat and a manual accurate gauge for temp is the next step.

I like doing 1 thing at a time to see if that solves the problem (the engineer mind of mine). So if the T-Stat and gauge don't solve it then it soudns like the fan clutch is next in line.

Thanks for the responses it is really appreciatted.

[Hubert]

When you replaced radiator and refilled did you burp trapped air with bleed screw in cross over? What thermostats do you have I think OE one is 180F and the other is 195F. Depending on your normal climate you might go with (2) 180's. Not that thermostats will solve overheating but might help with temp swings around 200F. There is still debate on best thermostat temp. Decide for yourself with a search. I want to say southern states EFI trucks most switch to twin 180's...maybe. I did at least and don't see big swings in coolant temp towing 9K (but less wind drag than rv). Decide for yourself with a search. Some like 195F coolant temp.

Towing that kind of weight you really should have gauges. They show you how the engine is loaded and responding to the load. Coolant temp is slower to react to load. EGT tells you how much heat is being generated in combustion or how hard the engine is working along with boost you'll know if its getting enough air. Low boost and high egt's will cause engine to run warmer. Also lets you know when its safe to shut off. Pulling a RV has a lot of wind drag and keeps the truck under load on the hwy even on level ground. Pulling into a rest area a pyro will let you know when turbo and heads (sort of) have cooled enough to shut down.

Gauges really help in diagnostics. You could be a tad low on boost and generating more heat under load but not bad enough to cause heavy smoke or set an SES light.

Extra gauges don't give any more performance by themselves but allow you to tune optimum performance levels.

[j_k_auto]

How does your radiator look? Pull rediator out and get all the crud out between the ac cond and the rad. This topic coms up alot in the summer time. Also make sure you clean your rad correctly.

Here read this.
http://blog.heathdiesel.com/

[lfytsmith]

I see you have 150k on engine. Ever replaced the injectors? I remember reading something about bad injectors adding heat to the engine. Talk to somebody at JK or HD and they recommend replacements at 100k. Gauges will definitely help keep you out of trouble. Boost and EGT are recommended minimums.

[sturgeon-phish]

At a minimum get the EGT gauge. Especially if temps are an issue.
When you fan clutch engages you can tell, even at full throttle windows up, A/C and radio on, if you have normal hearing. The first time my wife heard it she thought someting was wrong with the motor!
There is a test for the fan clutch engagment where you run the motor with the radiator blocked and monitor the temp. The fan should engage around 215. Like said before, before any part replacement, ensure you don't have air trapped in your system.
Your dual t-stat setup is my next mod.
Jim

[mkhagemann]

i bouight my first GMC C3500HD in 1995. It a 15,000 lb service truck. every hill i climbed in the Georgia summer temps went from 195-240 in thirty seconds. mentioned this to GM but," no comment". three months later "boom!" i got a new engine. GM engineering started listening to customers then. Ok by 1997 they did some cooling system mods, which helped alot, but i still wasn't happy. I also played with fan clutches, even help Kennedy with an electric clutch version. What i discovered to be the biggest problem is the radiator grill or aerodynamics, my trucks fan clutch sensed the heat at 68 MPH great, but run 55-62 MPH and you had a problem. the solution was, i didn't want to get in to changing the front grill so i increase radiator capacity. Griffin Radiator made me a custom radiator, now offered to the public. it is a 2 row (1.25") all aluminum, were as the factory is 2 row x 1". Now temps are within 10 deg of stat no matter what i do.

ASE Master Engine Machinist
1995 C3500HD - Lastest Gen Engine, every mod i could think of.
1995 C7500
1996 C3500HD

[More Power]

The GM factory turbochargers develop maximum boost pressure at 1800-2000 rpm. By 2500 rpm, the boost has fallen away to something less. Boost pressure is important to engine cooling. These 6.5's will run cooler at 2000-2400 rpm when worked hard. A boost pressure and EGT gauge will help you better manage the powertrain - and get more out of it.

An operating fan-clutch is absolutely vital to keeping things cool. Its importance cannot be understated. A fan-clutch that engages somewhere between 200 & 210 degrees engine coolant temperature will be able to stay ahead of the heat buildup, and help prevent the large temperature swings that might be possible otherwise. Engaging at 220-230 (or never) is too late.

Jim