rekomstop209

99 EX SOHC 1.6

Car does not always overheat, only seems to be overheating when I accelerate onto the freeway or up a hill. I suspected the thermostat was failing so I replaced it with an OEM part, but the temp gauge still rises, but it's delayed. The temp gauge doesn't start to go up until about 10 seconds after I've already put my foot into it. The longer I accelerate or keep the RPMs high is proportional to the amount the temp gauge goes up.

I suspected the gauge was giving me false readings because I've seen the gauge go all the way up now and I haven't seen any steam. But today I checked the engine with an IR gun and this is what I found. The upper radiator hose (return) was around 190-200 degrees F. The lower one was around 125 at first, EVEN THOUGH THE TEMP GAUGE WAS HIGHER THAN HALFWAY. After a minute or so of me tugging on the throttle cable, the lower hose did heat up to about 180, so I know the thermostat is opening. But the block was still reaching temperatures of around 225-230 degrees F, which I know is not good for the engine. Could the radiator be failing? Maybe not properly dispersing the heat? And if not, what else could be the issue?

The water pump was replaced about 6000 miles ago, so I don't think it's the problem, but is there a way to test it?

rekomstop209

New info to help troubleshoot:

It seems I can drive the car a pretty good distance, and get it up to atleast 70 as long as I baby it, I mean accelerating in 4th gear, never taking it over 3000 RPMs and the car does not overheat at all.

I took the radiator cap off and let the car run and then I tugged on the throttle cable and looked into the radiator and I can see the coolant rushing by so that leads me to believe that the water pump is turning when I give it gas, so I'm leaning towards it being a radiator problem because I honestly don't know what else could be causing that. It's like the engine is producing extra heat that the coolant cant compensate for, what could cause that?

100 + viewers and no one has any thoughts?

rekomstop209

I finally changed the radiator since the problem has still not gone away, and now the problem seems to be worse! After putting new radiator in I filled it to the top, turned the car on and put the heat all the way up and waited for the air to travel through the engine. It took maybe 10 minutes for the coolant level to drop so I could add more. I topped it off and capped it.

So now I get in the car to drive it around the block to see if my overheating problem is finally over and the car instantly starts overheating as soon as I drove down my street. Turned around, went back to my house, parked and popped the hood...the radiator fan isnt even on even though the temp gauge is at 80%. Perplexed, I just let the car run in park. Finally I just shut it off and then realize the fan is on! So I start the car again and the engine cooled down to maybe 70% (still way hotter than it should be) and then the fan kicked off and I could not get it to come back on again.

Is this an indication of a faulty ECT sensor?

Is it possible there's too much air trapped in the block and thats why its overheating?

Please someone help me, I really need my car operational.

axis11

Possibly more air trapped in the system. Park in an inclined area, front a little bit up. Open rad cap and run the engine. Top up the coolant as required. Rev the engine about 2k rpm to increase flow. wait till no more bubbles comes out and the fan has cycled on and off at least two times. Write down how long is the fan staying on at idle. How much clearance between the fan shroud and the radiator fins?

rekomstop209

I did what you said, parked the car in my driveway, let it run for atleast 30 min while topping it off as needed. It did bubble quite a bit so I know I got some trapped air out. But the fan hasnt even come on at all. And I just replaced the fan relay switch on the thermostat housing. Also, it seems like the thermostat wont even open because the lower radiator hose is not reaching 175 degrees, is it possible there is still air trapped right by the thermostat, thus preventing it from opening?

Car is running as I type, been going for like 40 min now. Not overheating...but no fan coming on.

rekomstop209

Just did compression test, all cylinders blew around 180 psi which is good, leading me to believe this is not an HG problem.

rekomstop209

Oh and the fan seems to be working now, if I let the car sit and idle, it turns on maybe every 4-5 minutes for about 20-30 seconds.

rekomstop209

Okay heres some new info, and i I think it may actually be the problem. Everytime my car cools down and I pull the radiator cap, it appears that the coolant level is a little low, like half an inch, but the overflow reservoir is damn near overflowing. So the coolant is going into the reservoir when the engine gets hot, but it doesnt seem to be flowing back into the radiator when it cools. It doesnt appear that there is a leak in the rubber hose running from the radiator cap flowing to the reservoir cap, so is it possible that the radiator cap is bad/wrong psi setting?

axis11

There have been many cases of new thermostats that are actually bad. Just for a test, run without the thermostat and observe the effects. Others would say never run without one. Observe the temperatures in both hoses and again record the time the fan runs and how long are the intervals. See if the coolant still goes to the reservoir and returns to the radiator when the fan runs. If it does not, replace the cap. If every thing becomes normal, install a new thermostat.