91 Es 250 Cooling Problem

[Mow]

I have a 91 ES 250 that is having a couple of issues.

I am loosing coolant to boil over. I can drive about 30 miles on the expressway and the temp gauge will not budge a hair over the second notch from cold. Then the needle will slowly rise a bit and well before it hits the halfway mark my air conditioning will start blowing warm air. I understand this to be some sort of safety device to prevent overheating. Anyway according to the temp gauge it starts to happen a little less then halfway on the gauge say 45%. Seems premature to shut off, I wondering what temp sensor or electronic device needs to be checked for this?

Any who, after the first 30 miles the engine is quick to overheat. Gradual inclines or cruising speeds of 65 mpg will cause it to over heat. I could literally stop and with the car in gear, hit the brakes and gas pedal at the same time and get the temp gauge very close to the red in probably a min or two. Normally I wouldn't try to simulate this but I live on a mountain. The elevations are about 1000ft and the road up is about a mile long. I never make it to the top without having to stop. What gets me is it takes about 20-30 minutes before I start having problems.

This is what I've done with the cooling system thus far; flushed the system a few times, new thermostat, new cap, replaced the top and bottom radiator hoses, I've used the bleed screw located on the inlet elbow when ever I've added coolant and just at random times to try and make sure that there is no air in the system. When all of the above failed I replaced the radiator. When that still didn't work I took the car to pep boys and had them block test it, and pressure check it. All test passed.

Had my fingers crossed that it wouldn't be a head gasket issue?

The cooling fans seem to work, there seems to be two speeds high and low and I've seen them both in operation. If I put my hand in front of the radiator I can feel a lot of air being pulled, so I think I am good there.

Here is what I’m thinking, and I guess I'm just looking for someone to validate or make a suggestion to my thoughts.

I may not be bleeding the system right, if there is a trick to this please let me know.

Or the thermostat I put in is faulty, it was not OEM it was AutoZone.

Or Pep boys lied and took my money and I do have a blown head gasket (which to me makes more sense because I'm good for 30 or so miles after toping off the radiator before any signs of a heat problem)

Or the water pump is failing even though the bearings appear to be fine and there are no leaks

Or the fans aren't working when I'm not looking? Or perhaps they aren't blowing as well as I think they are.

Could ignition timing cause this even though the idle is smooth and the engine runs good through all rpm ranges (while cold) once it warms up I hear what I believe to be valves chattering, and the hotter the engine gets the louder it is the less power the engine has, I believe some of that is pre ignition from carbon deposits. Which I read some interesting tips on how sea foam might possibly help, but I am afraid that it might push my cat into an early grave?

Anyway sorry for the long post any insight would be greatly appreciated.

[Xavier80]

hey Mow, i have a 92 es300 and although not exactly the same, i have similar symptoms. Did you figure out the problem