atkinson40

My temperature gauge was going wacky after replacing the head gasket. It pegged out a couple of times. I read that air in the system could cause this so I did my best to purge it of air.

After doing this the gauge was still going up almost max but the fans didn't come on and the thermostat was not opening because I could see no flow down the radiator cap.

I removed the thermostat and put a thermometer in the coolant in the cap. I can now see flow and the temperature slowly rises to about 200 degrees F and the gauge reads almost max.

What is the normal operating temp for a 1990 civic? At what temperature should the fans come on? Thanks kevin

ezone

Normal temps for ANY engine can vary a lot, but there are rules:

After warmup, lowest operating temp is determined by the thermostat.
Highest is determined by the cooling system and fan (switch), and the load on the engine.

Yours would operate between 180F (if that's the correct t-stat rating) to about 197F (fan switches ON) give or take a few degrees..

Book specs for the radiator fan switch are
Turns ON at 191-197F
Turns OFF at 182-188F



Sounds like you may have a bad temp sensor for the gauge.

atkinson40

I've removed the t-Stat, and the fans are not coming on at around 202 F. The temp gauge is almost maxed so I don't run it after the gauge goes up that high. I wanted to make sure that 202 F wouldn't hurt the vehicle.

I've replaced it. Also all this worked fine before changing the HG. Gauge never went above a little below half way. Something I did when I removed the head has caused problems. Maybe I got the wires wet. Or broke a wire, blew a fuse etc. The gauge, sending unit, everything was OK before HG change.

I did notice that I cracked the little boot that goes around the wire connected to the sending unit. Maybe I damaged the wire and caused an increase in the resistance of the wire. Thanks Kevin

ezone

Ummm
There are 2 temp sensors: One for the computer, the other for the gauge. Did you replace the wrong one?

Test the gauge? Remove the wire from the sending unit, make sure the gauge lays at or below cold.
Yellow/green wire
Ground that wire, then turn the key on-- the gauge should go towards hot.
WARNING: DO NOT LET THE GAUGE GO ALL THE WAY TO HOT, it may damage the gauge.



Ohm check the sending unit:
133*F = 142 ohms (C mark on gauge)
185-212*F = 49-32 ohms


Broke wire and blown fuse will result in a gauge that totally doesn't work.
Contamination in the wiring--- oil, coolant, etc., may have something to do with it.

HTH

atkinson40

I replaced the sensor that has the wire coming off that when shorted and UN-shorted to ground makes the gauge act as you describe.

I hope I didn't blow the gauge. I did this ground/unground test before being warned about possibly damaging it by leaving it go high.

The gauge works, just not what I would call normal. And its acted this way before I did the short/unshort test. It began acting up immediately after I started the engine after replacing the HG. It has a rapid fluctuation sometimes that I can't see being actual engine temperature because I don't think the engine temperature could change that fast.
I use diesel fuel as a degreaser and then hose it off to clean the engine. I suspect I got some fuel/water in a connector and its making the gauge act weird.

I removed the T-Stat and can see the water flowing in the radiator so I now feel comfortable the pump is working. I tested the T-Stat in a pot of water and it opens around 185 F so I know that's OK and will put it back in.

The fans are not coming on as I let the engine rise up to 200 F so maybe I have 2 problems. No fans and weird gauge. I'll put the T-stat back in today. Test the fans and look for contamination. Thanks Kevin

atkinson40

I put the t-Stat back in and ran the car up to around 200 F. The temp gauge was about 3/4 of the way up. The rad fan didn't come on. I turned on the AC and the AC fan didn't come on either. I remember reading about shorting the 2 wires together to bypass the switch and the fan should come on. Is this correct? Also what could cause both fans to not work? Thanks kevin

ezone

Temp switch, relays, grounds, fuses, fans, a ECM control for the AC fan operation, diodes....



You need a wiring diagram, a test light, and a DVOM now.

atkinson40

I was trying to figure out where the fan switch was and moved the wires that cross over the top of the fans. I must have a loose connection somewhere because now both fans come on when I turn on the A/C.

Also when the fans come on with the A/C, the temp gauge now falls back to about half way. Frap!! I hope I didn't over heat for too long and warp the head or cause some other damage. I've been going under the assumption that the car was not really overheating and it was a gauge problem. Drat!! Looks like the gauge was correct and it was getting hot.

Also the thermometer I've got stuck in the radiator cap falls from around 200F to 180F when the fans come on.

The fan switch is not in the T-Stat Housing on my car. If I understand the interwebs correct it's on the back of the block under the intake manifold. Is this correct? I see a couple of sensors with wires coming out.

Maybe I bumped a wire when I disconnected the intake manifold or got some water on the switch. I hope I didn't screw up my head by letting it get too hot.

Thanks kevin

ezone

You better find it and fix it before they quit again and you roast the engine.

Sounds average.

Yes, my pic shows just above the oil filter and toward the left (drivers side), 2 wire sensor.
The other one should be the oil pressure switch.

But it sounds like you need to find where the break is where you moved the wires and made the fans run up there.
That will probably take care of your problems as long as you didn't hurt the engine from letting it get hot. They do get damaged rather easily.



Maybe turn the ignition on but don't run the engine, turn the AC on, and if the fans run go move wires around try to make them quit running. Find the problem area that way.

HTH

atkinson40

Good troubleshooting idea. I'll try it. I think I have two problems.

One: The loose/intermittent problem that doesn't let the fans turn on when the A/C comes on.

Two: Whatever is not letting the radiator fan come on when the engine gets hot. The only way I've gotten the fans to run so far is by turning on the A/C. Thanks kevin

atkinson40

I turned the key on and A/C. Fans start up. I moved the wires around trying to get them to stop but they wouldn't. Not sure what was causing them to be intermittent.

I turned the car on and watched the gauge until it started to go over the half way mark. Thermomenter in the radiator filler only read about 175F and the thermostat had not yet opened.

I turned on the A/C to see if the fans coming on would bring down the temp gauge. Fans came on, but gauge went up a little.

With A/C on and fans running and thermometer reading about 175 should the fans be cycling on and off? Right now they are if I leave the A/C on, but won't cycle on and off if I turn off the A/C.

Thanks kevin

ezone

Coolant temp is regulated by the thermostat. Not warmed up enough yet, apparently.



Fan(s) MUST RUN when the AC compressor runs.
Does not matter what the coolant temp is.

HTH

atkinson40

I called the local Honda man and he said the fans cycling on and off with the A/C on is normal. A/C control of the fans evidently over rides the temperature control of the fans.

I shorted the two wires together that come off the temperature switch that controls the radiator fan and the fan comes on. This means the circuitry is working except for the switch. It still does not come on when the thermometer in the radiator filler reaches 202F. I'm going to pull the switch and test it somehow if I can.

I still don't like the way the gauge is behaving. If the cars is cold and I turn it on the gauge immediately goes to about 1/4 of the way up. Its also almost maxed out when the thermometer reads around 200F but is not consistent.

I'll get the fan switch to work right first and then worry about the gauge. I could always rig up an aftermarket gauge and bring it in side the car.

Thanks kevin

ezone

I called the local Honda man and he said the fans cycling on and off with the A/C on is normal. A/C control of the fans evidently over rides the temperature control of the fans.

Correct. As I said earlier, the fans MUST run when the AC compressor runs.
Independent of engine coolant temp.


It still does not come on when the thermometer in the radiator filler reaches 202F. I'm going to pull the switch and test it somehow if I can.

But is the temperature at the fan switch as hot as the temp at the top rad hose? Maybe not:
Temps down in the blocks water jacket probably aren't quite the same as the temps in the cylinder head. The head is normally hotter since combustion is up high in the cylinders.

The false gauge reading may just be freaking you out prematurely, but it is tough to rely on any of it until you know for sure if the fan switch turns on at the correct temp.
Might be worth replacing the fan switch just on general principles, since you will be pulling it out.

Use a pan of water on the stove, with a thermometer, to test the switch (hooked to an ohm meter or something).



I still don't like the way the gauge is behaving. If the cars is cold and I turn it on the gauge immediately goes to about 1/4 of the way up. Its also almost maxed out when the thermometer reads around 200F but is not consistent.

There IS a problem.......Ummm....
Is there a ground strap missing from the head or valve cover? (or large ground wire, maybe frayed and broken)


I'll get the fan switch to work right first and then worry about the gauge. I could always rig up an aftermarket gauge and bring it in side the car.

Those are pretty cheap, as long as you can find the correct thread size to go in the cylinder head where the original sender is.



HTH

atkinson40

In another life I was an electrical engineer. I learned that problems don't show up without reason. Somehow what's happening can be traced to something I did when I replaced the head gasket.

Before replacing the HG, there was no overheating problems. I could sit in line coming back from Mexico for over an hour without a problem. The gauge always read a little below half way.

The only symptom the car had is I'd loose about a glass of water every 100 miles with no obvious leaks where it was going. Not overflowing in the reservoir, not on the ground, nothing...... just disappearing.

I drove it this way for about 6 months until my anxiety got the better of me and I replaced the HG.

I believe something I did replacing the HG is causing this trouble. Like I said before, there's a reason for whats happening. I did end up with a mystery extra bolt. Its a 12mm head about 3/4 inch long and looks all rusty like the ones that came out of the exhaust manifold shield. For the life of me I can't figure out WTF it goes.

Fortunately my old beater 72 Datsun PU has stepped up and got me where I needed to go while the civic has been down. She'll carry me up into the mountains to Mexico to see my dentist this morning and when I get back I'm going to revisit where that bolt could go. If I'm missing a ground somewhere it would explain the problem.

Thanks kevin

atkinson40

I replaced the fan switch just for good measure. Maybe the old one was working and I just didn't let it get hot enough to close. The fans now come on at a radiator filler thermometer reading of about 202F. They only run for about 30 seconds and shut off. This brings the temperature in the radiator filler thermometer down to about 190F.

The gauge in the dash now doesn't get above half way ever. It varies a little below half to half. It just mysteriously stopped going up to almost max. I don't think I can attribute its return to normal to changing the switch because the engine wasn't getting any hotter before than it is now.

Maybe I got water on the wires somewhere and its gone away. I'll watch the gauge and drive cautiously for a while. Thanks kevin

sekhonjatt

This is bit relavent to this thread. But i am facing similar heating issues with my 99 civic ( i know this is thread for 5th gen, but nobody replied to my thread )

My engine is slightly overheating. I had my older civic where the temperature would stay below the "E" sign but my current 99 honda civic almost reaches the half. So could you please tell me if thats normal or am i goin nuts

ezone

The "E" is for fuel level, not the coolant temperature.

The pic of the gauges: Wouldn't worry me one bit. The coolant gauge isn't even near the halfway point in that pic.

HTH

atkinson40

I put a "Tee" in the coolant line that goes from the T-Stat housing to the intake manifold. I then installed a mechanical temp gauge in the "Tee" top so that coolant was running across the sensor.

I can now see the new temp gauge slowly creep up to about 190 degrees as I drive the car. Its not going wacky as the cluster gauge is. The cluster gauge still jumps to almost max.

Is this a good place to put the sensor? Is it really indicative of the engine temperature as the original is that is in the head? There's no engine drain plug that I could get to, to install the sensor.

Also, I hope I got the hoses back on the T-Stat housing correct. One goes to the heater and the other goes to the intake manifold. Which one goes where on the T-Stat housing? I think I might have got them reversed. Thanks kevin

ezone

Does that help?

atkinson40

Yes it does! Thanks. I have it hooked up right. I put the "Tee" in line "8" in the diagram on the right. I'm hoping that this is indicative of the engine temperature.

Right now the cluster gauge is going up when the car is moving fast and comes down when the car slows down. Not when the engine is running fast, but when the car is rolling fast. I can be on the freeway and put the car in neutral and the temp will not come down until it slows down. Then I put it in gear and the temp will not come back up until the car is moving fast. This is confusing?? All the time my mechanical gauge that I put in line "*" is solid as a rock around 190 F.

I've replaced the cluster sending unit below the dizzy with no result. I'm beginning to think the voltage to the sensor is fail. When I first start driving, within about a half mile the cluster gauge creeps up really fast to about half way. The new gauge slowly moves up to 190 F and stays there. I'm confused.

I'm going to measure the sensor resistance when cold/hot. At least this will tell me if that part of the head is really getting hot.


Thanks kevin