I've been fighting this overheating problem for quite a while now on my 1994 F350 w/ 7.3 IDI Turbo, here's what’s going on.

It only OH’s when I’m towing my camper (about 7500#) and working the engine such as on a grade). Even with outside air temps about 70 degrees and going up a 5% grade at 50MPH at 2500 RPM in 3rd (Automatic w/ OD switched off) after about 1-3 miles it will heat to the point the Overtemp light comes on.

Here’s what I’ve done so far; without being able to correct this problem

1. Had a new radiator installed prior to purchasing the truck.
(This was verified correct radiator and a new one by a Ford dealer).
2. Replaced Fan clutch (ouch $$)
3. Replaced Injector pump and Injectors w/ New ones and timed at a local Diesel shop (it was the original w. 180K miles on it)
4. The fan and shroud are original and in good condition.
5. Flow tested the water pump and radiator
(Both flow good).
6. Replaced the thermostat twice w/ Ford one.
7. Installed dual electric 14” fans in place of the original one
8. Removed thermostat

I wonder about my turbo, I understand if a turbo is bad it can inject hot air and cause low performance and overheating problems, is this true? How difficult is it to remove the turbo to test it without it?

I’m completely out of ideas; if someone can help I would really appreciate it.

 

What does your guage say the temp is?
Do you see hot on the guage about the same time the light comes on?
In step 7 am I understanding you removed the stock fan and installed two electric fans?

 

The gauge does not have temp numbers, but instead has "N O R M A L". The light comes on when the gauge reads at "L" (The top edge of the displayed scale). When it's there, I can hear the water boiling and it's spitting water into my overflow.

 

I have the same problem, so am posting to recieve emails about it. Let me kow if you find anything, and I will do so also.

 

I know this sounds simple, but has the system been flushed chemically? This improved my cooling system.

 

no, i didn't do so...

 

When you are pulling the grade with your camper on, are you like on the floor with the throttle and 50 is as fast as it will go?

Do you have a pyrometer?

Did you remove the stock fan and install two electric fans? Or did I miss read that?

 

I had a real bad overheating problem which was almost completely cured with new antifreeze, a new AC condenser, and pressure washing the fins of the radiator. I have a 1994 CC dually Turbo diesel. I pull a 34' gn trailer to work everyday. It weighs 8 to 10k. My problem occurs at higher speeds, I have no problem going 70, but if I try to go over 50, it'll get hot. Now, I can do more like 65, but the first long hill does me in. i do not have a pyrometer, and have not touched anything on the truck, and do not plan to. I run real cool empty. My temp does not go down very fast, it will not ba back down at the bottom of the hill, so the next one is worse. A lower gear makes it even worse. The last time I got real hot was when I tried to go 50 or so and downshift. It seems to be rpm dependent, not throttle dependent. My fan clutch locks up tight and I get a lot of airflow.

Here is what I have been wondering, and I do not want to hijack the post, but this may help the other guy. Could a sticky injector or the timing help this. If I took it to a dealer and had it dymnamically timed would it help? I don't know what any of it is, but I got all that out of a Haynes manual.

Check the fins of the radiator. Mine had so much crap in them that no air could get through. FWIW, I had my turbo tested prior to purchasing it three weeks ago, and I still have the smae problem, so that could be it. What about the exhaust?

 

I have a '90 that only heats up at high rpms, shift into 4th and go up a hill or pass and bang its hot, any other time it is fine, the only thing we have found is the rad.

 

I'm going to guess a whole bunch here, but these are the things that I have learned in dealing with the heat out here in Nevada in cars and trucks of all kinds used mostly for hard work and high speed running at 100+ mph.

Electric fans cannot keep up with the heat generated by most engines when they are under heavy load and the vehicle is moving or the engine rpms are up. They only work best at fast idle, no load-no a/c at 12-1500 rpm with the vehicle moving slowly or stopped. Anything else and a good mechanical will out do them 2 to 1. However if you put the electrics in front as pushers with the mechanical you will get the best of both worlds combined. As with many things too much speed can also kill you on the heat. There is a little known phenomenon that occurs when the airspeed trying to enter the radiator outpaces the capability of the fan blades to get out of the way. It is called propeller stall in airplanes and basically means that the fan becomes a block to the flow rather than pulling it. This usually only happens at speeds in excess of 100 mph, but depending on the type of vehicle and the fan/radiator/shroud design, I think this can happen at lower speeds in trucks.
I too have noticed the tendency for my diesel truck to overheat as with most of the diesels that I have ever driven or owned when you downshift and run them hard. My theories are that there is something wrong in the engine or with the airflow. I am leaning toward too far retarded timing that is allowing the burn to continue too long and cause overheating in the exhaust port and manifold/turbo. I may just be guessing, but I know that a gas motor can do this if the timing is too far retarded, or advanced and pinging, but mostly when it's too far retarded.
As far as the airflow problem. I don't really know what the fix is. Maybe the water pump is running the water through the radiator too fast at high rpms for it to cool down? Or if the tubes in the radiator are clogged internally it can be too slow to cool down. I don't have an engineering degree, or access to heating studies, so I can't say for sure what is going on. I do know that when you run most gasoline engines at above 5000 rpm, they will overheat unless you have a really good waterpump that is designed to reduce cavitation of the impeller, or slow the pump down with a bigger pulley and smaller crank pulley. As for airflow. You really have to work to increase it much in most vehicles. You can have the hood louvered and vents placed into the fenders, but that can be expensive and ugly. You can try to put in more fans, or change the way they run. Or you can rig up a water spray system for the radiator to cool things down. Any way you go, there is work involved.
If you overheat at low rpms pulling a hill, then look for airflow problems, or possibly too much antifreeze in the mixture or clogged radiator either inside or out, just because it's new doesn't mean that the tubes arent plugged with crud. With the antifreeze anything over 50 percent will not cool as efficiently. Also try grabbing a lower gear, or higher one. That really depends on your setup and the egt's that you get. Lugging a turbo will definitely not do good things for it, and sometimes you just have to back out of it a little and accept that you can't be the first one to the top of the hill.

Good luck and if anybody has any other ideas, I'm very receptive to learning anything new or better.

 

Wow, what response, Thanks to everyone for contributing.

I have not chemically flushed the system, how do I do that? I was also reading on a earlier post about having the "correct" anti-freeze. So that's the next thying I'll do since I lost all of the old "NAPA" stuff.

I don't have a pyrometer, would like one, but I'm spending all my money trying to fix this. Other then the information, will it help me diagnose the problem?

It heats up pulling my camper at 3/4 to full throttle, I normally can control it at 1/2 throttle, but then I'm down to 35MPH. It heats up on the flats at 65+MPH (With the camper) as well, but it's always OK unloaded.

I did remove the stock fan and replaced it with dual 2600 cfm 14" fans, didn't help, maybe even worse but I put the stoke one back on.

I cleaned the bugs from my condenser and spent a hour with a small screwdriver straightening the fins. I did notice a noticable improvement by removing my grill.

What about my Turbo or Exhaust? How can I test them without actually replacing them?



Thanks again to all

 

If you had the pyrometer you will probably scare yourself.

On my reman 7.3 turbo diesel with stock fuel settings I can run up a 10% grade at 70 MPH empty.
The pyrometer will run right up to 1200 degrees, it would go more if I let it.
As far as that goes I can get it hot enough running down the flat road at 90 MPH that I back out of the throttle because the EGT's are to high.

That oil coming out of the turbo is picking up lots of that heat, this is removed by the oil cooler and added to the coolant heat that the radiator must remove.
The oil and coolant is trying to cool those pistons and heads that have a 1200 degree fire inside the cylinder.

A turbocharged diesel can melt the pistons and turbo if you do not watch the EGT heat. Pistons start melting at 1250, the turbo will start deforming the blades at about 1270.

Dragging 15,000+ pounds up a 5% grade makes a lot of heat that you have to get rid of.

You may be trying to go faster than you should be up the grade.

 

Thanks Dave, I guess I will need to get a Pyrometer and put a scare into me.

 

Chemical flush can be done at any shop. It requires an special machine that pulls all the old out. Then replace with proper antifreeze and additive to stop ellectrolysis (cavitation).

 

my fan clutch is bad. It will go from totally locked up to freewheeling. I know you replaced that, but when it was locked up, I ran real cool, even today with the AC on...