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

 

Does your van have a closed loop coolant syatem of a straight overflow to ground line coming off of the radiator cap?
Do you see changes in the coolant level ? Is your thermostat in the right direction? Could be it's sucking air somewhere in or around the water pump?
Lots of questions, no answers off the top of my head.

 

sounds like bad thermostats to me. i have seen a friend of mine get 3 bad thermostats in a row exchanging them for the same brand. get a real thermostat the only one i will buy is the stant superstat cost me $4.35 here is a link to there site. http://www.stant.com/brochure.cfm?br...ocation_id=168

 

Thanks Garysvan I will be installing the third thermostat this weekend and this one is a Stant I'll let you know what happens.
ALAN

 

jpsarte12 I have a closed system. With the cap off and the level in the radiator drained so it is just above the tubes the level goes up and down about an inch or so.
ALAN

 

Could the hose from the filler neck to the puke tank be bad? If so, maybe it allows hot water to go into the tank, but sucks air back into the system when it cools.

Here's a long shot...Drill a 1/8" hole in the thermostat. Some thermoststs have these. I'm not sure if it allows the air to bleed off or what, but I'm sure you've seem these.

MR

 

I have the same problem with my van, I just replaced the thermostat from a 160 degree to a 190 degree and now my gauge shows it overheating. I hooked a prolink scanner up to it to monitor the data and my engine coolant will heat up to 217, then the thermostat opens and drops back down to 169. It shows as extremely hot on the gauge, but the info on the prolink says normal range when it hits it's peak in temp. I figure it has to be a bad gauge. Haven't checked for air bubbles. By the way I put in one of the failsafe thermostats thats supposed to lock open in case of an overheat.

 

I always thought mine ran hot with 192 (i also tow). So I put a 180 stat in. It runs fine and temp is ok. It still gets heat as I drove it last night and it was 4 deg outside.

 

More info - I just installed a new Stant thermostat with the arrow pointing toward the radiator. The hose from the radiator to the overflow tank is ok. I bought an infrared point and shoot thermometer and started cking temps all around the engine & rad. Here are some of the things I found (but I'm still perplexed). When the temp gauge on the dash is past the L, the temp at the sender is 235; at the intake manifold side of the thermostat it's 200 and it's 100 on the radiator side of the thermostat. After about 30 seconds the thermostat opened and the temp on the rad. side of the thermostat went up to 190 & the manifold side came down to 190. But after 5 min. the bottom of the radiator was 88 and the water pump housing was 130. At that time the temp on the back of both cylinder heads was close to 200 and the back of the intake manifold was just over 200.

More- with a piece of clear hose connected to a T in the heater hose and held above the hood, when the engine is restarted hot, the coolant is about 6" above the heater core. As soon as the fuel injection slows the idle speed down, the coolant level drops and the hose empties.

So I clearly have some kind of flow problem....remember I have a new 4-core radiator that has been removed and flow checked. This van has A/C & a serpentine belt. Is it possible that I have a water pump for a V-belt type engine? That water pump would spin the opposite direction. Anybody have any ideas?

 

hey doc , how about a hair line crack in a cylinder wall that only gets exposed and opens up when the engine is running?hows that for a blast from the past? i think your having a flow problem ,if the problem started at the replacement of the water pump that should be the first thing you change out , parts folks have been known to send the wrong parts ,mechanics have been known to install those wrong parts, myself included,your idea about the reverse rotation is right on the money, take two asprin and call me in the morning, good luck, bob

 

I had this happen on a 83 Ford van. Thought it was a problem with the radiator so replaced it, but the gauge was still showing that it was overheating. Took it to the shop - was stumped. Turned out to be the negative battery cable connector was corroded & not making good contact with the chassis. Since they cleaned it - have had no more problems. The gauge reads dead center all the time!

 

I had a 86 Dodge van that I bought in 1990 that overheated all the time. I complained to dealer that sold it to me but I had bought it as-is. But it wouldn't pass emission test. Turned out it had a cracked head. They replaced the head and one piston. I still have the van and it has about 275k on it. It had 56k when I bought it.