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I've noticed on my 94 Integra (bought used about 2 weeks ago) that the thermostat is often below cold, sometimes above cold but never up to the center mark.

Today I was boiling inside my car as it was a very hot day and my thermostat was below cold for the engine. Any ideas whats up? From searching it seems like the thermostat might be broken but I don't understand why sometimes it goes above cold.

Cheers!

EDIT: I guess I should be more specific: I've noted that the engine temp reads below C even after 30+ mins of driving. Sometimes it will be around 1/3, but usually its below C even when I've been running for quite a while

pwee92
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    On most cars, the thermostat will always be below C until the engine has been running at least a minute or two, and should never go over about 1/3 the way up to H. – R.. GitHub STOP HELPING ICE Jun 25 '12 at 05:28
  • Hmm okay. I guess I should be more specific: I've noted that the engine temp reads below C even after 30+ mins of driving. Sometimes it will be around 1/3, but usually its below C even when I've been running for quite a while – pwee92 Jun 25 '12 at 05:39
  • Sir, I have the same situation with my civic EG, it has a JDM B16a transplant, whenever the key is turned to ignition, it turns on the radiator fan continuously, it is no longer connected to the thermostat and the relay, we usually do that here in the Philippines. The thermostat has also been permanently opened, thus always keeping the engine constantly cold, it almost never goes up to even 1/4 of the temperature gauge, the engine was already like this when I bought it. Although it is very useful to prevent overheating of the engine, I'm planning to buy a new thermostat and reconnect the radia –  Aug 05 '13 at 08:21

3 Answers3

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Not sure if this is the same on the Integra, but on my 2003 SEAT Leon I have the same issue, and the cause I believe is that the thermostat is stuck open - this is either due to a failed temperature sender unit (so the thermostat never gets the signal to close) or the thermostat itself needs replacing - that'd be the first places I'd look.

kgfullerton
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    Thermostat sticking open is a very common failure. – Brian Knoblauch Jun 25 '12 at 14:58
  • OP, what's your climate like? Where I live, it's hot enough that even with the thermostat wide open the engine won't stay at C... – R.. GitHub STOP HELPING ICE Jun 25 '12 at 16:06
  • I'm living in Vancouver, the highest temperature I've driven in is probably around 60-70F (18-20C). The issue isn't that it won't stay at cold though, it barely ever goes above cold (excuse me if I misunderstood).

    I drove into work (hour drive) at probably about 12C and my thermostat was at or below C the entire trip

     – pwee92 Jun 25 '12 at 19:58
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The coolant system is designed to keep the engine at a near constant temperature. If the temp is too cold it affects fuel ecconomy and performance. If it is too hot engine parts overheat and get damaged. The thermostat does this by opening and allowing hot coolant into the radiator to be cooled. When the coolant temp is low it closes and allows the engine to warm to the designed temperature.The are three most likely causes. A defective thermostat that stays open. This allows the coolant to flow thru the radiator and actually overcools the engine. It could also be a defective gauge ot sensor. The other cause is a defective coolant fan relay. If the radiator fan runs constantly it can also overcool the engine.

mikes
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  • Depends on the application. Engines are designed to get up to operating temperature quickly and then stay there - primarily for emissions control and efficiency. It won't hurt the engine to run cool, though it might add pollution and hurt MPG. Better to underheat than overheat, however. – geoO Jan 02 '15 at 04:07
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As others state, it could be related to your thermostat. Depending on the operating temperature range you could test it in water and check at which the thermostat will open.

Another issue that you might want to check is how accurate your gauge really is. You might want to install an aux. temperature gauge and sender to monitor accurately your engine temp. My gauge on my 1987 Land Cruiser is more an indicator than anything else.

Gabriel Mongeon
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