1996 Chevy 3500 6.5TD overheating

[ttyR2]

Looking at a '96 3500 with a newish 6.5TD. Reports are that it smokes a lot, doesn't have much for power, and will overheat if pushed. I'd imagine the smoke problem is related to the fuel injection system. Where should I start troubleshooting?

With overheating issues, is that usually signs of a cracked head, assuming the rest of the cooling system is working?

[Big Green]

Check for leaky head gaskets first.

[Robyn]

Bad head gaskets will show up real quick, as the coolant will puke out the overflow.

Overheating is likely a result of a plugged radiator core, T stat thats not working right or a fan clutch in bad order.

Be sure that the area between the AC condenser and the radiator are not plugged with crap.

The radiators in these rigs are not sized very much past what they really need and over time the internal tubes "SILT" in in the lower levels with crap and this reduces the flow.
Also all the tubes that are flowing tend to gather junk on the internal surfaces that insulates the tubes some and reduces the heat transfer rate.

The best fix is a new Visteon replacement radiator. Stay away from the cheap replacements as they use epoxied core contruction.

The smoking (BLACK) can be due to restricted intake system.
Very probably the vacuum pump or related control systems have stopped working and the turbo is not supplying any boost.

Make sure that the Turbo wastegate actuator has about 15 inch HG at the little hose connection.

A failed vacuum pump may or may not set a code. A failed wastegate solenoid should set a code.
The plastic vacuum lines could be broken too.

Keep us posted

Missy.

[Beavis]

I've just started encountering overheat issues while towing (guessing 5-6k lbs)

The weird thing is, at high speed all works fine, even up fairly steep grade. This is while maintaining close to 60mph. You can hear the fan engage properly, guessing around 180-185 degrees on the gauge. Then it pretty promptly cools down. This is even in cases where it has to downshift to 3rd. The only time I've seen this new problem is when towing at low speed.

When towing slowly uphill, (not really because of extreme grade, but because of posted limits/curves in road) the 6.5 starts to heat up fast. And I never hear the fan engage like it does at highway speeds. Like I said, it doesn't feel like the truck is maxed-out when this happens, I just have to drive slower than normal due to road conditions. The first time I noticed it, I was just getting into boilover territory, and I couldn't hear the fan at all.

My first instinct is a bad fan clutch. I'd think if it were the thermostat I'd see it all the time?

The truck is a '99 GMC 3500 with 115k. I was told by our local GM garage though that the 6.5 plant was replaced in 2003 in this truck, around 83k miles at the time. It does have a Goodwrench tag on the block.

[6.5TDTahoe]

When you get stuck at low speed travel move the shifter to 2. Rev the engine up to 2500 RPM or more. Air flow thru the intake,heads & turning the water pump @ higher RPM will have a positive effect on the increased rcooling ability. Now if the engine is blowing black smoke & water temp is climbing don't operate in those conditions. All the cooling improvements are needed,if not already in place. Overeating the engine & continung on the course can be disasterous

[Beavis]

Thanks for the tip.

I looked at some of the fan clutch fan combos. Do you think I need a fan sice this was a later model with the 9 fin fan?

Also I read about using a dmax clutch and fan? Is that a good solution or are the aftermarkets still better?

[JohnC]

If it's an automatic, at low speeds the torque converter is unlocked. The trans cooler is inside the radiator, on the cold side, so the air the fan clutch sees is not hot; the water gets heated by the trans cooler just as it exits the radiator. (I think...)

[Robyn]

With a 96, the radiator is likely getting to the end of its service life.

Unless there are other issues here, a fresh Visteon radiator would be a good idea.

Over time the radiator "silts in" and the the tubes begin to plugg up with crap on the inside.

Now you may want to pull the grill and make sure that the area between the AC condenser and the radiator is not partially plugged with crap, blocking airflow.

The issue is that at higher road speed there is a lot more air being pushed through the grill and this helps the fan a lot.


My feeling after seeing the same thing with my 95 3500 truck, is that the radiator is probably unable to do the job any more.


Robyn

[Beavis]

John, so if I'm reading you right, even a thermal fan clutch isn't going to help since the fan isn't seeing the heat that the coolant is receiving from the transmission?

What's the best solution? Reworked transmission cooling? Some other solution that will run the fan based on fluid temperature?

It is an automatic.

[JohnC]

the fan isn't seeing the heat that the coolant is receiving from the transmission

Good question.

When I had my manual '93 I never had the slightest hint of a temperature issue. The automatic '95 ran much warmer under pretty much all conditions.

The heat added by the trans cooler results in warmer water entering the engine. This may cause you to run up against the thermostat and other flow restrictions quicker. A lower temp thermostat may help, but, bottom line is if the fan isn't kicking in then the radiator must be shedding enough heat on its own. The higher temp you see on the gauge is really a non-issue as long as it stays under control. Cooling systems run into trouble when the heat absorbed exceeds the heat shed for any length of time. As the temperature of the water in the radiator increases, the BTUs shed increase too. If they reach equilibrium before the temperature exceeds a safe limit then all is well.

Adding an air-to-air cooler for the trans before the radiator, or moving the existing one to before the radiator, might help, too.