OVER HEATING! Need Solutions? 1996 GMC 3500 6.5 TD

[entrusted]

PLEASE HELP.

I have a 1996 GMC 3500 6.5 TD w/185k that is over heating when I haul my 5th wheel. The 5th wheel is about 13500lb. It should have no problem haul that weight, I thought? What I have done: 1. new thermostate from a 190 to a 180. (I discovered it is a Nov 95 model so it has only 1 stat, other 96 models have 2 stats) 2. new fan clutch. 3. had radiator checked and scoped, machanic said it is crystal clean. 4. heater works very well so I think the water pump is good??? 5. transmission was just rebuilt. 6. just did a full tune up. its still over heating!

what is the tow capacity of this truck anyways? It's a 1 ton crew cab daully.

Anyone have any ideas of what to do?

fyi. it's fine unless I'm hauling and primarily going up grades at low mph 28-45. Power declines and it hit up to 255+ from 200 in about 10-15 min. and I have to pull over. When I go on a straight or down hill temp lowers.

[ercaduceus]

IMO you should update the coolant system to a duel t-stat system. Also if the front of your water pump does not have "HO" casted into it IMO you should up grade to a high output water pump. All of that aside the easiest thing you can do is completely remove the radiator and clean all of the fins. Even if the inside is clean the outside fins are what cool the water.

Good luck

[a5150nut]

How is your exaust system, stock? Open the exaust, larger pipe and free flowing. Are you running trans locked up or converter range? And how is your air filter? And as was said how clean is the outside of your radiator?

Pulling this kind of load I would be looking at a set of gages, pyro, boost, and trans temp and the minimum.

Also what gearing and tire size are you running?

So many questions...............

[Warren96]

The plastic cover over the top of the radiator and fan blade comes off with a half dozen 10mm bolts which exposes the space between the air conditioner and the radiator.Mine was plugged up with leaves. If you haven't cleaned yours, that can be a problem. Also running at 2800 provides MAX cooling, running at 1800 provides MAX MPG. Let us know if this helps... Good luck!

[Mark Rinker]

13,500# is alot for any 6.5. No matter how efficient your cooling system, you are going to see temperature spikes when running hills, on hot days, etc. Everything stated here previously is pointing you in the right direction.

First things first:

Completely debug the radiator, oil cooler, tranny coolers, removing all bugs and debris stuck between them.
KennedyDiesel.com sells an upgraded fan clutch that will flow more air, engaging earlier, releasing later. If you just bought a new, but stock fan clutch, return it and spend the money on a Kennedy. This might take care of your problem all by itself.If not, then try this test. Remove the single thermostat completely. (I ran one of my 1994 3500s without a thermostat yearround with nothing but lower temps in the summer, and the same temps in the winter.) If it helps, you can leave it out until/if you upgrade to the dual thermostat system. What this test tells you is you need MORE COOLANT FLOW...

You can continue to perform the following upgrades in order, based on how much you want to spend, and effectiveness.

Dual t-stat system and HO water pump.
3 1/2" or 4" exhaust system to carry heat away faster.
Heath Turbo-Master wastegate control. Too low boost wastes power, and generates more heat into your oil. Bringing up boost to about 9-12psi nominal will make power you need, and lower engine temps.
Gauges and a performance chip
Good luck!

[Jochen Woern]

Hello there and good evening,

I had exactly the same problem with my '96 Suburban pulling a 26' Foot Travel trailer uphill, overheating was a big problem.

I agree with what everyone else so far wrote and I would advise as well to do the following in order:

1.) Make sure your radiator is clean, take it apart and clean thouroghly from the outside, you will definitely find bugs, leaves, debris behind it. Remove the plastic shroud cover in order to find all that junk.

2.) I already had the dual thermostats on my Burb, since it was built in late '96. I would highly recommend as already mentioned below to upgrade the system to the two thermostat with High Output water pump scenerio.

3.) Next I installed an Aftermarket Air Intake in order to let the truck suck more air. (The original stock air intake IMO is terrible). In my case, I used an "aFe Stage 2 High Performance Air Intake Kit". Cost me about 225 bucks brand new on eBay and is worth every penny. The truck does now provide more power, you will reduce the EGT (Engine Gas Temperature) and you will hear the turbo whistle.

4.) Next, upgrade your exhaust system. I went to a 4" inch Jerry Jardine, Pinnacle Power Exhaust System, available on eBay for 285 bucks plus shipping. More Air in, More Air out.

5.) Next I will install a Heath Diesel Max. E Torque Computer upgrade with a Manual Turbo Boost and of course the Gauges in order to keep an eye on the EGT, Boost and Tranny Temperature.

I would also advise to remove the plastic grey "TURBO POWER" piece in the Engine Compartment. It does restrict some of the heat below/underneith it. Get rid of it, it is only there for looks and IMO does not belong there in the first place.

This all should help for sure.

GOOD LUCK!

[mkhagemann]

I have a 95 and 96 3500HD, both had the problem you have. definately upgrade the cooling system and fan. Most people don't like to spend the money on a good radiator, but I'm sorry but its the best solution. Call Griffin Thermal Products (1 800 722 3723) give your application, with their part no. you can order through Summit. this will increase the rad from 1" to 1.25" tubes. I use 180 deg stats and never go over 210 pulling a combined wt of 27k. Keep in mind 6.5s don't like temps above 230, this usually causes the head gaskets to go or even worst the cylinders tend to crack near the head bolts! some kind of intercooler will help greatly. the 6.5s pulling that much wt will begin defueling as the temp goes above 210, we all know too well those embarassing hills that brought us to a crawl. good luck

1995 C3500HD Dmax intercooler, 18:1, Garrett Turbo, Griffin Rad, 4" stack, NV4500
1996 C3500HD , 4L80, 18:1, spearco cooler
1995 C7500 Caterpillar 3116, 10 speed

[entrusted]

I already upgraded the exhaust to a 4" flow through system and I upgraded the air filter to a high flow through K&N, did complete tune up, still over heating.

fyi. I took the truck to the dealer today and they did a leak down test??? for the cooling system. they said the system is fine (17 lbs of pressure for over 20 min) no leaks, T-stat and fan clutch work fine and the engine seems fine. They said the truck is only rated for 10k (truck and trailer) so that's why it is over heating-it's over loaded. I don't understand, the truck alone weight probably 3 ton. So I can tow 4000-6000lbs??? Doesn't make sense? I see trucks pulling bigger 5th wheels than mine all the time.

Anyone out there pulling a 13500 lb 30' 5th wheel or simular with a 1 tone daully 6.5 TD with no problems? What is the true tow capacty for that truck, anyone know? On the side of the door it says 10,000 gvw. what does that mean?

I will look into the other suggestions you all made. I think I will thoroughly look at the radiator 1st and clean it then change out the water pump. the daul t-shat and HO water pump, where can I find them at a reasonable price? I just sunk $3k into the tranny and I'm really low on funds. or maybe one of you guy may have one or know someone who has one for sale?

Thank you again guys, this is my first time here and my first diesel truck.

[Mark Rinker]

Did you try my test of removing the thermostat completely? This will tell you if your overheating problem is flow related. It sounds like you are still looking for a solution through tuning - your only solution for hauling a camper that large is MODIFICATIONS. This has all been done before, by the people here. Your dealership will be glad to charge you lots of money, but won't suggest the needed aftermarket componants to make your 6.5 heavy tow capable!

Your truck will have no problem towing 8-10K# once you have addressed the coolant flow issues - i.e. dual thermostats, HO water pump and Kennedy fan clutch, although you won't gain any more power than you have today. By adding a chip and more boost, you'll be able to march up and down the hills, but not until you have the heat issues resolved...!!! Don't overheat that truck too many times, or you'll be swapping engines instead of water pumps.

I noticed you didn't mention anything in your response about replacing the fan clutch. Don't discount this because you have purchased a new one, and your dealer said its working okay. Your stock fan clutch is underratted for the weight and wind drag you are trying to tow! Again, in order of importance to your engines longevity:

1) Fan clutch upgrade (can be effective without dual thermostats and HO pump)
2) Dual thermost upgrade (can be effective without HO pump)
3) HO water pump upgrade (needs dual thermostats to be effective)

Here is the info on GVW and GCVW...

10,000# GVW (Gross Vehicle Weight) means your truck can carry 10,000# - (truck weight + driver + gear + fuel) = something around 3,000#.

Not to be confused with GCVW, (Gross Combined Vehicle Weight) which is the manufacturers rated max for truck, TRAILER, gear, fuel, passengers, cargo, etc. This number is very conservative, as it is GM's lawyers that have to stand behind the trucks ability to STOP this 'combined load' safely.

To further cloud the muddied waters, you can license your vehicle and trailer for well over the GCVW total. In most states, cops and DOT officials will add the truck and trailer tags together, and check to see that the tags don't exceed the GVW of either. (If they want to want to write you a ticket, they will compare that to the GCVW rating on your truck's doorjamb. Most don't.)

Last thought: If you just spent 3K on your tranny, you should investigate a deep tranny pan for additional fluid capacity...Hughes makes a nice one.

If your intention is to haul 13K worth of camper, you may want to investigate a used Duramax. Your 6.5 can be modified to handle the load, but have a high incidence of catastrophic engine failure, especially when run hard, turned up, etc. There are many older LB7 DMaxes available that would handle this load in stock form. Just a thought, an option...

[drewkeen]

Take the radiator out and clean it. I was doing a flush anyway so I figured it wouldn't hurt to clean mine out. It looks pretty clean but when I cleaned it sooooo much nasty crap got all over the driveway. I don't see how it could have fit that much junk in it, but somehow it did. Also make sure you get the AC condensor and the auxillary coolers in the front while you have the radiator out.



Also, another thing you can do is add some redline water wetter to your coolant. I've never used it on a truck but it works great on road courses and high performance car engine...Don't see why it wouldn't work in a truck.

[Kennedy]

Lots of good advice here. My suggestions (not necessarily in order)

Clean the air side of the radiator. The coolant side will be clean.

Good performance exhaust. 3" is a bit small.

High Capacity water pump kit/dual stats etc

Special calibration fan clutch and 20" steel blade

ECM tuning (aka chip)

INTERCOOLER!

[sturgeon-phish]

I looked in a sales flyer for 96 GM trucks and the dealer flyer has a max trailer weight of 8000# for a crew dually w/ a 4.10. Now I'm sure this is conservative to prevent a lot of warranty issues. Hard to believe, I tow my 29' 5th that goes 10K loaded
Jim

[entrusted]

a friend also told me that there is a water injector unit from www.snowperformance.net, anyone similar with this?

[Mark Rinker]

Water injection can make more power by cooling the intake charge (chemical intercooling) of turned up 6.5's, but would not be an effective mod, without the coolant flow modfications discussed here. It would be a logical modification after cooling mods, after chipping and turning up boost, adding gauges, etc.

Basically, its a way to intercool the engine, without adding an intercooler.

[entrusted]

another question: how reasonable is it to say after modifications that this truck can really pull 13500 lb?

[Mark Rinker]

Its overloaded.

Can it be done? Yes.

Can it be done cost-effectively? Maybe

Would a newer Duramax K3500 be a better choice? Yes

Assuming you pull your 5'er less than 20 days per year, it might make sense to invest in the truck you have, and then save for the truck you want, later on.

My opinion - for what its worth.

[entrusted]

Mark Rinker, we are full timers so we will be pulling the 5'er quite a bit. but we will be stopping at different places for a week to a couple months at a time. so it will get a rest at times.

what I'm doing currently: cleaning the radiator thoroughly, taking out the t-stat then I will take it for a test drive. hopefully that will work for the mean time. then when I get more $$$ I will get the kennedy clutch, daul t-shat, HO pump. What is the cost I should expect to pay for all that and where is the best place to purchase them?

also, I noticed the truck is having a hard time starting up in the morning now. its been colder here in Az but not under freezing. maybe on average high 30s - 50s at night. I tryed starting it up late morning (temp 60s-70s) and had to try starting 3-6 times before turning over and smoke comes out the exhaust. is that a glow plug issue?

thank you, Jeff

[Mark Rinker]

Sounds like a good approach. Since you are in Arizona, I now understand your overheating concern. Its a long pull up the hill to Flagstaff from the valley.
Call John at KennedyDiesel.com regarding the fan clutch. Not sure on prices.
You might post under the Classified section a 'WANTED' ad for the dual thermostat crossover, and the HO water pump.Starting problems.

Search this forum, and READ READ READ on this topic. Hard starting can be due to bad glows, low compression, weak injectors, weak injection pump, incorrect injection pump timing, or a combination of all of the above. In general, older 6.5's are smokey, hard starters compared to their newer GM brothers. However, there are things you can do to drastically improve that.
First - check all battery and ground connections. Good starting - starts with good cranking.
Check and clean all connections to your glowplugs, many times you'll find a couple no longer working due to corrosion or bad connections
If you are getting short glow cycles, consider replacing the glow plug relay.
If you still have problems, replace all 8 glows, but get ready for a wrench-fest on the two near the turbo...Its all been done and documented here...read read read!

You are welcome. We all started here asking similar questions!!!

[entrusted]

Mark, just to let you now the hard start is a resent issue (last 2 week sense I been in Flagstaff, Az.). in southern calif. it started up right away every time w/no smoke. but once it starts and warms up the rest of the day it runs like a champ. I hope the over heating didn't damage the engine. what's your thoughts?

I'm not a mechanic so I'm learning how to do things myself. I do know where the batteries are so that's a no brainer, I will check out all connections.

fyi. I just took out the t-shat and ran it down the road w/out a load and the temp is about 170 - 175 seem to run significantly cooler, about 10-15 cooler. also I took the shroud off and sprayed out the radiators. man, there's a lot of radiators on this thing. 5 all together, one really large one, one about 3/4 its size in front and 3 small one infront of that one. anyways, do I necessarily have to remove all of them or could I just pressure wash them installed?

thanks, Jeff

[BillCarry]

I have a '94 motor home which weighs about 15000 lbs. Owned since new. Have 150K miles now.

I learned the hard way back at about 85000 miles to keep the exterior of the radiator debris free. Now I pull the a/c condenser back every two years and clean the radiator face. I did the HO water pump upgrade also. The motorhome engine came with a single, larger thermostat. I do not have any overheating problems any more. This engine is pulling 15000 lbs everytime it moves and sure seems up to the task. I also admit that I don't try to win races going up steep grades and I watch both coolant temp and EGT when doing so.

Bill Carry

[JohnC]

Manual trans trucks seem to do a lot better as far as overheating goes, thus I think the trans cooler in the radiator has a lot to do with it. My recommendation is to put the biggest trans cooler you can fit between the trans and the radiator cooler.

Oh, do all that other stuff, too!