I have a 99 Civic EX D16Y8 SOHC 1.6

About 6 weeks ago, I noticed my temp gauge was getting very high as I was accelerating up the on ramp onto the freeway. But when I reached 65, I coasted and the gauge went back down to normal operating temperature.

Checked all fluid levels, everything was fine. Water pump and timing belt had just been replaced 6000 miles ago. So I replaced the thermostat since its the cheapest part. Problem did not go away.

I found that if I babied the car, and accelerated very slowly, I could drive the car quite a distance, and get up to 70 mph without the temp gauge going up. But after a couple weeks of driving like a grandma, I noticed the temp gauge going up again even while I was babying it. So I ordered a new radiator and put that in just the other day.

Theres no bleeder valve on the 99 so I just left the radiator cap off and let the car run for like 45 min, filling the radiator as needed. Took the car for a drive, the temp gauge still went up with hard acceleration so I parked it and popped the hood and noticed the radiator fan was not on even though the temp gauge was at like 80% (way too high). The fan eventually came on, but I decided to replace the fan relay switch on the thermostat housing anyway. Car still overheats.

So now I move onto a compression test, thinking I have a breached HG. All cylinders had PSI around 180, so HG is intact. Spark plugs looked pretty clean. Theres no white residue on my exhaust pipe.

So now I'm thinking that the radiator cap that came with the new radiator is faulty so I went to autozone and bought a new one, however it was DIFFERENT then the one that came with the new radiator, which had a washer about an inch in diameter. The one I bought from autozone had a washer about 1 cm in diameter, but both are rated for 15 PSI. I'm not really sure which one to use, but I put the autozone one on.

This seemed to help a little. I can drive the car again while babying it, but the temp gauge still rises if I accelerate too hard so I'm basically back to square one with a nearly completely overhauled cooling system and still having an overheating problem.

Is it possible the car is not actually overheating and the ECT sensor is just faulty? Because through all the overheating over the weeks, I never once saw steam come from the radiator or smelt burning antifreeze.

Someone please help me, I really need my car fully functioning and at this point I'm really out of ideas. The only other things left to replace are the hoses (pointless because I have found no leaks), the cooling fan relay (pointless, because fan works) and the ECT sensor, and I guess I could run a flush/cleaner through the block. Unless anyone has ANY OTHER ideas or advice, I would REALLY REALLY APPRECIATE IT!

ANY INSIGHT IS WELCOME, PLEASE!

I've had this problem posted on civicformus.com for weeks and only one person has replied!

 

Is the radiator staying full? Check it with the engine cold before you start each trip. It must stay full to the top.

Fan is actuated by the temperature of coolant leaving the radiator, not the temperature of the engine. If no coolant is flowing the engine can overheat even though the fan switch doesn't get hot enough to trip on. You can just jump the switch to make the fan run all the time for a test.

Also when you're driving check that the heater always works. If a bubble of air forms in the top of the engine typically the first symptom is the heater stops working. A slow leak in the head gasket can cause such a bubble to form even though the compression tests normally.

 

Actually, I have been letting the car cool and checking the level on a regular basis and it is not staying 100% full. It is only like 1/2 inch low, sometimes I can just barely see the top row of fins, but the overflow tank is way full. Its like when the coolant gets hot, it expands and flows to the recovery tank, but never flows back into the radiator. I usually just end up lifting the recovery tank out and pouring some coolant back into the radiator, but I dont want to have to do that multiple times a day.

After I replaced the radiator, i dont think I bled it all the way, but I actually bled it this morning for about an hour, there is most likely no air left in the system. When I run the heat, it stays hot constantly.

 

Turned out to be a blown head gasket. Just wanted to post this in case anyone else has a similar problem.

I was able to confirm it was a head gasket breach by getting a smog sniff on the radiator; it detected 343 ppm, it cost me $20...I had already spent $180 trying to solve the problem by replacing parts.

If anyone has problems similar to this, get a smog sniff immediately, its much more accurate then a combustion leak test and its so quick and cheap.

 

So did you end up replacing the head gasket and fixing the problem?

 

Yep, as stated above, the head gasket was leaking and causing combustion gasses to rush by the ect sensor in the coolant passageway and was giving me false overheating. Replaced all gaskets and had head decked. Problem fixed

 

Thanks for the advise. I seem to be having the same issues. I did the radiator cap, thermostat, new coolant, and bleed it for 30 minutes. Did you replace the head gasket yourself? I was just wondering how much it would cost to get my head gasket replaced at a shop?

 

I did not replace the hg myself, you have to completely take apart the top half of the engine to gain access to the hg. Its a lot of work, lots of parts to keep track of, plus, engine will need to be retimed. I took mine to a private mechanic and he charged me about $1000, but that included taking the head to a machine shop and having them deck the head and pressure test it, which I highly reccommend u have done too, else you risk blowing another hg

 

So the moral of the stoy is don't throw parts at your car until you know what the problem is.

 

Wrong. Sometimes the only way to troubleshoot with no CEL is to start by replacing cheap parts that could be the culprit and work your way up to the more pricy ones. It wasn't so much the parts that were a waste of money, but the damned $50 chemical test on my radiator that ended up passing!

The real moral of the story is that a smog sniff is far cheaper and more accurrate than that chemical **** at determining if there is an hg breach in the cooling passageway, which apparently is the most common way the hg breaches on the D16Y8.