My 93 Ford E150 (351 V8, 120K miles) has developed an overheating problem that has me stumped. It has always run at normal operating temps, but then it developed a leak at the water pump and I had that replaced. It developed the overheating problem at that point specifically - the shop that did that repair (who I consider to be knowledgeable guys) told me about this new problem before I ever picked it up. Their attempts at fixing it included replacing the thermostat (twice), replacing the water temp gauge sending unit (twice), removing the radiator and having it flow checked (it was ok), and replacing the water pump again. They pressure tested the system looking for leaks-none found. Somewhere in the process they did a chemical block test looking for combustion gas in the cooling system and found none. They finally threw in the towel and I picked it up from them.

The overheating problem surfaces once the engine gets up to normal operating temperature, then the temp gauge goes all the way to hot, stays there about 30 seconds, then returns to normal. This happens about once every 5 minutes. It doesn’t seem to matter whether the van is sitting at idle, driving around town, or driving at freeway speeds.

Since I brought it home, I started checking for air in the system. I added a T-fitting in the heater core return hose, connected a 3-ft clear hose to that T, and held the hose above the hood. There’s a flow of air bubbles coming out of the hose – sometimes a lot, sometimes just a few bubbles – but it’s a constant flow of air. Yet I’ve done a pressure test myself on the system (twice - once letting it sit overnight with pressure on it) and there’s no drop in pressure, so I’m confident that there’s no leaks. Where is the air coming from? Occasionally the system creates about 4 lbs. of pressure. I bought a Napa Block Tester which checks for combustion gas in the cooling system but the test came out negative. I’ve had the radiator hoses off twice and checked for delamination inside of the hose, but they seem ok. I’ve drained and refilled the coolant (twice). The second time I refilled it I followed the Mitchell and Motors manuals procedure which requires removing the heater hose from the water pump and filling the radiator until coolant comes out the fitting, then replacing the hose and filling the system the rest of the way. It didn’t change a thing.

To be sure that the temp gauge is not the problem, I put an ohm meter directly on the water temp gauge sender and got ohm readings that matched the temperature change.

After 30+ years of fixing cars, I must admit, this thing’s got me stumped. Anybody got a new idea?

Alan

 

how about the radiator cap or the fan clutch, if you are just boiling the water there may not be an actual air leak? a real old test for fan clutches ' and im not going to repeat it, there are to many young folks that read this, and my hands tell to many stories of early ways to test things, im sure they have better ways to test them nowdays, good luck,bob

 

bob, check out my post in the 1968-present full size vans section wherein I have lots more info posted. I've checked the fan clutch (and didn't lose any fingers in the test!) and it's ok. I replaced the radiator cap early on in this process. I'm sure I'm boiling the water and that's where the air is coming from. Again, see other post. Maybe my long saga will trigger something in your brain to help. Thanks, Alan

 

hey doc, see my reply under the van section, bob