I have a '91 e-250, 300 ci with automatic. About 30 miles into a trip this morning at 65 mph I started to run hot and hotter. I got off the highway and while sitting idleing, the gauge dropped like a rock to normal. Back on the highway it ran hot again. I returned home on a secondary road at 45-50 mph and it was normal. The oil pres. gauge move from way over to the left back to normal a couple of times. Are my gauges fooling around with me? I changed the plugs recently and removed the thermostat and I have not taken a long trip at highway speeds in a long time.
I need some help so I can resume my trip. Thanks Lloyd

 

You'd at least need a voltmeter to be able to test the gauges, but they're not particularly accurate in any case. Stop at a parts store or Wal-Mart and buy an automotive thermometer to stick in the back of the radiator where the hot water comes in (the higher hose). Stick it between the radiator and fan shroud near the inlet and start driving. When the gauge goes hot, quickly pull over and check the thermometer. If it's close to 220°F, then you have a screwy gauge and you can diagnose it when you get home. If it's up around 270°, check the pressure of the upper hose, and see how difficult it is to make the lower hose collapse.

 

Thanks Steve, I'll try that. I bought a mechanical gauge, but, have not installed yet. After further diagnosing it, I have some small bubbles( a very fine foam) flowing from the direction of the top hose, across the top tank. I suspect a bad headgasket.
lloydbob

 

I doubt it - just the slosh at the water pump will generate a little foam. But any radiator shop should have an exhaust gas test kit that will show if the head gasket is leaking. I don't know how much they charge, though.

 

Thanks again for your imput.
I borrowed a pressure tester today and as I revved the engine the pressure climbed towards the 30lbs that the tester people suggested I not let it go over.
I know I should change the headgasket and if it were my old F-150, I would not hesitate. As it is a van, and misserable to work on, I am trying to put it off.
What do you think(as a temporary measure) of the 'Permanent Metallic Block Seal products, like the one put out by CRC?
Lloydbob1

 

Where were you testing this pressure? I don't know anything about that CRC seal - I stick to direct-replacement stuff.

 

I was measuring it at the radiator cap with one of those pump it up testers for seeing if the system leaks. What I don't understand is why the 13 pound radiator cap did not open up and dump out on the highway when my temp. needle was buried?
Lloydbob

 

The cap probably did open, but the fluid went to the overflow bottle. If you let an engine sit and idle with a pressure tester on it the pressure will almost always climb higher than normal because there is nowhere for it to go. The real question is did the cooling system hold pressure after it was shut down? Lots of times when there is a coolant leak the system won't even build pressure because it escapes form the leak. With a head gasket it usually builds pressure very quickly because combustion pressure is leaking into the cooling system. A fairly easy way to check engine temp, although indirectly, is to use an AC thermometer in your heater vents. The heater temp is usually within 20 or 30 degrees of engine temp at normal operating temperature. If you drive with the heater on you should see a heater temp rise at the same time the gauge goes up. Unfortunately, this is a sucky time of year to do this.

Some other things to check for are blockage of the radiator both internal and external. Overheating on the highway is usually either an airflow restriction or low coolant level. If you're burning coolant you should have steam at the tailpipe, but not always.

 

I don't have an overflow bottle as I don't have, what I believe is called a closed system, and it never came out of the overflow, until I pulled the release Interestingly enough, My heater core started leaking last winter and I bypassed it, so I can't take a measurement there. I did buy a mechanical temp gauge and I will install it.
lloydbob

 

Replace your cap and consider adding an overflow tank.

 

I cant get my 4.9 to warm up at all but I'm not complaining! I like a cool engine! Now I'm using a 160 deg thermostat and it still keeps everything just below normal and without a thermostat the needle wont move. Mind you that I'm using a solid fan with no clutch on it.

 

If the engine doesn't warm up, the computer will keep it in open-loop mode, and run it rich all the time. It wa$te$ ga$, generates a LOT of HC emissions, and the buildup of gasoline in the crankcase will thin the oil and ruin the engine.

Since the OE gauge isn't very accurate, you should buy a dial thermometer (~$8 at Wal-Mart with an A/C pressure gauge) and see what your ACTUAL engine temp is. If it's low, I'd recommend fixing it.

 

I am running a 160 deg stat in my 84, she sit right around 160-180 no matter how hard I run her.