1990 Accord LX Overheats
 

In the spring of 2004 I had a new radiator put in with new hoses and cap. I then installed a new thermostat (170 degree) myself. Most of the time and most of the year everything is fine. When the weather is warm and the AC is on, the temp guage starts moving to HOT. I turn on the heat and it comes back to normal right away. This also happens if there are 5 adults in the car on a warm day and we negotiate hills and stop-and-go traffic. In other words, whenever the engine is taxed on a warm day it overheats. This does not happen on the higway even with AC on. There is a bypass of some kind (at least I think that's what it is) in the thermostat (a hole in the flange with a loose pin in it that apparently opens and closes). Could I have installed the thermostat the wrong way(not backwards but with the bypass on the wrong side)? Could it be the thermo sensor for the fan (by the way both fans work). Finally, there is no coolant leakage so I assume the water pump is ok and there does not appear to be any bubbles in my coolant. I'm not sure the mix is 50/50 but would that really make this kind of difference? I would appreciate any suggestions. Thank you.

Re: 1990 Accord LX Overheats (Omaha1)
 

Try a cooler temp thermostat, also have your system flushed and refilled with an higher mileage coolant mixture...sounds like either your thermostat is not optimal for your engines requirements, or your system isnt flowing correctly.

make sure that both fans are working properly and coming on on time

Re: (deserthonda)
 

^^^ Also a good idea...the cooling fans can cause the engine to overheat at standstill if they are not working properly.

Re: (hypnosisracing)
 

If this happens when negotiating hills, then that's an indication that there may be either air in the system, blockage in your [new] radiator, or the thermostat is installed wrong - or may not meet the requirements of your motor.

Did you install the thermostat with the bell (loose pin) on the up side of the thermostat and not the lower? If you did this correctly, the thermostat may still be no good. Did you use an aftermarket thermostat or an OE? It's not uncommon for an aftermerket thermostat to be faulty. OE is the safest way to go with those things.

Try bleeding the cooling system thoroughly. Set it on a pair of ramps or jack stands to simulate an incline, drain the radiator, then run some water through it to flush it out. Distilled water is good to use for this. Plug the radiator and top it off, then put a bleeder funnel into the neck and fill it half way. Start the car and run the heater on full blast. Let the car warm up to "normal", and then goose the accelerator, wait 2 minutes and then goose again. Repeat this procedure for about 10-15 minutes after the car has settled to normal temperature.

By goosing the accelerator, you are revving it to about 4-5k rpm and then letting go DON'T HOLD IT DOWN.The key is to let it settle at idle between each goose. Without the radiator cap on the system can't really build up pressure so the goosing of the throttle from idle gives it a bit of pressure by speeding up the pump sharply[going from idle to high rpm instantaniously]. A sastianed high rpm will not achive that same effect. Once you feel confident that the air is gone, then replace the radiator cap and top the reserve bottle and drive off!

Finally, if the first 2 aren't your issue, your radiator may be blocked. Replace it and check it again.

i would check to make sure that the fans are plugged in all the way.

Flush the system and refil. you can check to see if your rad is clogged by taking to to a shop and having them flow test it.

Re: (YeuEmMaiMai)
 

when was the last time the water pump was replaced? I'm not saying this is the case but I've seen it happen where they go bad before the bearing/seal fails.