My ambulance at work is a 1996 E350 P/S. The truck has 170,000 miles on it. It has been over heating at high speeds, around 80 mph is when it starts. The water pump was replaced around 9 months ago, the thermostat and fan clutch were replaced last week. The truck runs great, idles all day long in 100 + degree heat and never gets hot. The Ford dealer can't figure out why it gets hot and neither can the other shop we take the ambulances to. It doesn't leave puddles of coolant any where, and never takes more than a quart of water every couple of weeks to top off the over flow tank.

This is a real pain in the butt. I want my ambulance back the back unit I'm using is a pre P/S 7.3L and is guttless. Any ideas for me to check out?

 

I would suspect a radiator problem. Check the outside of the radiator and a/c condenser for bugs, leaves, etc. The best thing to do would be to remove the radiator and send it to a radiator repair shop to have it cleaned and flow tested.

 

I second checking radiator for external blockage of air flow and, if there is nothing there, pull it and send to a commercial radiator shop. 80 mph puts a pretty good load on an engine especially with the wind resistance and weight of an ambulance body.

If they find any problems you can ask about installing a thicker core in your radiator - I have done this on three cars/pickups with great success when towing. The Power Stroke radiator may or may not be able to have this done but it is worth asking about if you need it recored anyway.

Dave / Believer45

 

Yep....radiator. Might be clogged up with stuff on the outside, or might have some kind of clogging build-up on the inside. I might add that when you put it back together, be sure to use distilled water to make your 50-50 mix with the antifreeze.........

 

Was it overheating before you changed the thermostat? There is much confusion on thermostats for the 96-97 powerstroke. Until 1996, all 7.3L Powerstrokes that were manufactured used the International thermostat and water pump. In 1996, Ford changed water pumps and therefore changed the design needs of the thermostat. The thermostat in the Powerstroke not only controls operating temperatures, but properly directs the flow of coolant through the engine. With the International (Pre-96 Ford) thermostat, this cannot be controlled properly because of the shorter bypass stem. The shorter stem of the IH(pre-96 Ford) thermostat allows the thermostat to be fully open while the bypass is fully open. This means the coolant can travel in any direction available -- whatever direction it chooses. Be sure you got the stat with the longer stem. If the stat is the right one then I would check out the radiator. I got the information on the thermostats from Dieselsite. You can read more about them there.

 

The thermostat was changed to rule that out as a cause of the over heating. It was changed out by the shop not me so i'm not sure which one was used.

Everything you guys pointed out makes sense. I will suggest to my boss that the radiater be taken to a shop and checked out along with the thermostat. Was the thermostat a mid year change?