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Old 01-13-2012, 04:04 PM   #1
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Default "overheating" but thermostat doesn't open and fans don't come on?

Edit:
recently replaced the waterpump, radiator and cap, upper and lower rad hoses, and the sender for the gauge. Gauge is still going into the red despite my thermometer saying water temps are not surpassing 175F at the thermostat housing when the car is running.




My temperature gauge keeps maxing out/going into the red on my 93 while driving, but only goes up to two bars (right in the middle) when idling. The car doesn't boil over when the gauge is maxed, but the heat inside the car does get noticeably hotter.

I thought the thermostat was the problem so I replaced it with a 180 and still had the gauge going into the red

I then bought another thermostat, only a 170 this time and a new rad cap and still had the issue

both Thermostats tested out fine when placed in water around 180 degrees

I've drained and refilled the system several times with straight water and I've even run a bottle of radiator flush through. Yes I make sure the system is bled thoroughly too.


For now I'm just running an open thermostat (an old one that I forced open) and the car mostly sits at 1 bar on the gauge and the car will not go into vtec



The car originally had an h23 which I replaced with an h22 last year. I was negligent and didn't replace the water pump, so I'm unsure of it's condition. I also broke my thermostat housing a couple months back and noticed that the new one already has a lot of deposits on it, so maybe that has something to do with it?

I also have no reason to believe that the sensor is wrong, but I have new one coming in the mail anyways.


Any help or input is appreciated..

Last edited by Johnrb; 04-18-2012 at 02:48 PM.
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Old 01-13-2012, 04:27 PM   #2
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

A bad water pump would overheat all the time, not just at idle. Your radiator itself might be clogged, but first you need to figure out what's wrong with your fan. First just make sure the fans and thermoswitch are plugged in (since you've had the motor out they may have been forgotten). Then you need to test them. It's usually one or the other
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Cool build! I cant really tell what is what from the pictures. I also like the fact that you have a KNN air filter, those are a must!!! Just swap for a V-TECH head and youll be set!
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Old 01-13-2012, 04:43 PM   #3
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Bad thermostat, the fan switch is on the other side of the thermostat. If the thermostat doesn't open, the fan switch doesn't get hot, the fans don't turn on.
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Old 01-13-2012, 05:12 PM   #4
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Or temp sensor A is bad and not opening.
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Old 01-13-2012, 05:20 PM   #5
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

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Originally Posted by InvaderTrax View Post
A bad water pump would overheat all the time, not just at idle. Your radiator itself might be clogged, but first you need to figure out what's wrong with your fan. First just make sure the fans and thermoswitch are plugged in (since you've had the motor out they may have been forgotten). Then you need to test them. It's usually one or the other
The fans were working before today (they were actually on anytime the ignition was on due to the sensor on the thermostat housing).

After I changed ECT switch A and B with junkyard parts I noticed that they don't come on now even when the AC is on..

They're definitely plugged in and I've tried two different relays and also checked the fuses, but I'm not getting anything out of them.. Time to consult the helms I guess
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Old 01-13-2012, 08:19 PM   #6
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Get a small wire, pull the connector on ECT switch A and bridge the connection in the plug. Both fans should come on. If they dont come on you have a bad relay, fuse, or control module. If they do come on, the ETC switch is bad.
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Old 04-17-2012, 08:57 PM   #7
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

decided to throw parts at the car to try and solve the problem..

replaced:
waterpump, thermostat, radiator, lower rad hose, white ect sensor in the head, and the black ect switch b on the front of the head.
Car idles at 2 bars on the temperature gauge (normal operating temp) but still goes into the red while driving even with the fans jumped on. When the car is "overheating" the water in the radiator is not boiling and I see no obvious signs that anything is wrong. I'm stumped

Any ideas?

Going to try a usdm ecu tomorrow and thoroughly bleed the system. The car runs under operating temperature (1 bar) without a thermostat and only has this issue when the thermostat is in, but the thermostat checked out fine in hot water and works perfectly as it should.
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Old 04-18-2012, 08:14 AM   #8
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Have you checked to see if you have blown a head gasket or cracked your head? I would do a compression check and maybe a block test if the compression check looked ok. Have you tried to read your spark plugs? Do they all look the same?
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Old 04-18-2012, 10:50 AM   #9
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

210 psi across the board, no visible differences in the spark plugs. They're all a little light brown.
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Old 04-18-2012, 11:06 AM   #10
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Water pump would be my next guess. I have seen pictures of them degrading; it might not be completely bad, but cannot move enough water to keep it cool. The fact that it stays cold with no (or stuck open) thermostat is a bit odd though.
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Old 04-18-2012, 11:35 AM   #11
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Is this the proper bleeding procedure?


With the car OFF:
turn the heat to full hot, but keep the heater fans off, open the bleeder until there is a constant stream through the bleeder while topping up the radiator up to that point.

Last edited by Johnrb; 04-18-2012 at 11:52 AM.
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Old 04-18-2012, 12:37 PM   #12
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

I had the same problem too last year. Try adding a ground (ValveCover to firewall). See if this solve your problem because it solved mines. Doesn't hurt to try. I know, real mind blowing!
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Old 04-18-2012, 12:42 PM   #13
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

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I had the same problem too last year. Try adding a ground (ValveCover to firewall). See if this solve your problem because it solved mines. Doesn't hurt to try. I know, real mind blowing!
Sure enough it was this^

Lol thanks for the help guys. I had a suspicion the car wasn't actually overheating. Even before I replaced everything, but i figured it wasn't a bad time to overhaul the cooling system.

Last edited by Johnrb; 04-18-2012 at 06:29 PM.
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Old 04-19-2012, 07:09 AM   #14
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Default Re: "overheating" but thermostat doesn't open and fans don't come on?

Ground problems can be a bitch. Glad you got it figured out. I have 3 extra grounds on my car for cheap insurance. one from battery to head. one from intake to chassis, another from chassis to valve cover.
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