1996 6.5 overheating problem

Hey, a couple of months back I acquired a new to me 1996 chevy 3500 That has the 6.5td and 4l80e transmission. When I got the truck it needed an injection pump because the previous owner stole it for another truck. While I was in there I put a new water pump on it and relocated the pmd to the fender. The trucks been running like a champ and daily driving it it's never got over 170 degrees. The other day I finally retired my old rig with a 6.2 diesel and nv4500 because it needed a commercial tag to run so I needed something to tow my tractor with for work. The 6.5 really dosent like towing all that much apparently. You can't run the ac or get much over 50 because you can watch the temp gauge rise steadily if you do and I don't like running stuff at 205 degrees. It also seems to be gutless compared to the old 6.2 diesel but that's another problem. Why is it getting that hot, it has a new water pump and fan clutch. The 6.2 never got above 190 pulling the same load. Also the wastegate and vaccum pump are working. Any help would be appreciated

How clean are your radiator and condenser ? Trash tends to collect between them and oil cooler. Separate and clean if needed.

Do you have a boost gage? Air filter in good shape?

If gutless and all else is good, I would think maybe timing is a little off.

To begin with, 205° isn't excessive. If it's manageable at that temp, it's fine. The instrumentation, at best, is questionable. If it is, in fact, that temperature, and you want it lower, install lower temp thermostat(s).

If your 6.5 is producing less power than your 6.2, something isn't right, and the SES lamp should be on (for a variety of reasons). If it's blowing black smoke, the turbo isn't turbo-ing (check the vacuum pump operation). If no black smoke, the fuel is restricted (either the supply (filter?), or the computer is defueling). It could be other reasons, but these are the most common.

I have not checked for trash yet but that's a good possibility, the back side looked really clean but that really doesent mean anything come to think about it. Air filter is clean, it has an aftermarket cone on it that was there when I got it. I don't have a boost gauge yet but that's on the list, you can hear the turbo spool like it should and it dosent smoke at all. The timing could be at fault, but it fires right up and dosent seem to be off but I've been wrong before. It runs like a sewing machine and will out run a 2004 half ton gasser, it just dosent like pulling a small tractor. I'll check the stuff with the radiator when I get home

The only time the SES light has been on was for a shift solonoid b for the transmission, that was fixed a month after I got it and it hasn't come back on and it dosent smoke at all even under load and it has a new lift pump and fuel filter

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Originally Posted by Tim01

I have not checked for trash yet but that's a good possibility, the back side looked really clean but that really doesent mean anything come to think about it. Air filter is clean, it has an aftermarket cone on it that was there when I got it. I don't have a boost gauge yet but that's on the list, you can hear the turbo spool like it should and it dosent smoke at all. The timing could be at fault, but it fires right up and dosent seem to be off but I've been wrong before. It runs like a sewing machine and will out run a 2004 half ton gasser, it just dosent like pulling a small tractor. I'll check the stuff with the radiator when I get home

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Air filter..... "Aftermarket cone", like a K&N? Under the hood? This presents issues, especially during hot summer towing. Pulling in hot underhood air not only increases the intake air temp, but also the engine coolant temp. This can cause the PCM to defuel (less power), as well as providing much less dense air (also less power). A cold air intake system (1997+ OEM, round), or aftermarket "cold air intake", goes a long way to minimize this. I was referring to the fuel filter, but the air filter could certainly be in play.

The 6.5L runs pretty hot. It doesn't take much towing to see the temp gauge climb quickly. In 1997, GM upgraded to dual thermostats and a high-flow water pump. That will help when towing and is a good swap to perform on pre-1997 vehicles.

Also, the stock GM fan clutch is terrible. It does not engage soon enough. I bent the tang on the coiled spring on the clutch so that it now engages as soon as the temp starts to rise. That one mod has helped tremendously on my 1995 6.5L.

Casey

AEM makes good cone filters.
A 7 inch base on a cone filter fits nicely into a 7 inch duct pipe. That duct pipe is cheap. Add a 7 to 4 adapter to attach to the headlight opening in the front with a 4 inch flange. Run 4 inch flex hose to your turbo. That and wide gorilla tape worked for me. You will need to plum your CDR hose in on the suction side and maybe an air filter gauge. Don't forget a silicone adapter to clamp to the turbo and put the hose into.

The timing should likely be within specs as the computer will scream if things are off very much.

As mentioned... THE FAN CLUTCH on these is crap and the aftermarket stuff is little better.

As Maverick mentioned 205 F is fine.

Notice that the RED zone is 250 F :eek:

Pulling hard in hot weather the truck should be able to maintain 220 F and not go over that.

As mentioned the TWEAK to the fan clutch bimetal spring to get the fan on when the temp hits 210-215 helps a lot.

YOUR STOCK RADIATOR may be silted in down in the inner part of the tubes.

These radiators are very marginal when new and a bunch of miles will render them lacking in cooling ability.

Visteon makes a fantastic OEM or better unit that's quite affordable.

If you elect to replace the unit...

Flush the block and heater core/s with clean fresh water until things are very clean and free of all antifreeze.

Refill with standard GREEN Glycol coolant that mixes 50/50 with water.

With the block flushed well and with clean water add pure coolant first (a gallon of pure and then 50/50 to top it off and get a good freeze rating.

Stay away from the RED STUFF.

You can add pure water in a pinch and then replace with green if need be.

The red stuff is a PITA if you lose some and don't have any red handy.

As mentioned, make sure the stack is clean between the various coolers.

Also...
NO lights or other goodies allowed in the NOSTRILS in the bumper..

The two holes in the bumper are critical to keeping the proper air pressure in the cooling stack.

It's amazing the difference it makes.

One little trick that helps a bunch is to remove the aluminum cover that goes under the radiator and bolts to the front frame cross member.

This allows waaaaaaaaaaaay more airflow into the engine bay.

I found this out on my Dahooooley 6.5

With the pan off the bottom the thing stays much cooler.

When the thing is hot the fan should come on and ROAR... IF IT DOES NOT then the fan clutch is not working right.

John Kennedy sells (or did) a clutch that comes on at a lower temp.

The 6.5 makes a buttload of heat, and it's in the heads being a precup engine.

When things are right they will stay cool.

Another trick is to use the DMAX fan blade

There are articles on this modification.

Getting massif air flow through the stack is the real deal.

Air moves heat.

If the heat can get to the fins in the radiator then the big blow can make it go away. :)


Be sure of the cooling system parts and then go from there.

A stock single stat set up will work fine (not as good as the dual stat with the high flow pump) but use a 180 F stat.

The stockers are usually 190 F or 195 F and they are rated at these numbers at JUST OPENING.

The 180 F will start opening at 180 F and be full open by 190 F.

A lower setting stat will not fix a plugged stack or cooling tubes or a fan that's not working.

Good luck