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Brief description of my problem: Upon cold starting my car, it will take roughly 10-15 minutes for the factory temp gauge to even begin to move. Im sure this could be very normal on most cars however...my real issue begins when i actually start driving, once the car is under load or i am driving up a steep hill, the temperature will shoot up to 76 degrees, (pretty standard i think) Although the second i start driving down a hill the temperature reading will drop dramatically, usually to just below 50 degrees, that is, so the factory temp needle has returned back to the bottom.

 

Variabilities/changes: Facts and things i have noticed or changed in an attempt to fix this, the motor is an sr20de running a stock radiator and a new thermostat. A clutch fan in good working order (swapped the old one out).

I also have, a device to read the figures the ecu is picking up from the temp sensor. And a water temp gauge (defi) fitted in the upper radiator hose. This means i have two separate readings giving me roughly the same information (usually 3-2 degrees either way). Around the time this issue started i lost use of my aircon, it now just pumps out hot air. Coolant was flushed with new coolant put in, changed nothing.

 

This problem has been going on for about 6 months and so far its not proved to be any sort of a serious issue however its just really confusing, id be really interested to know if anyone has had the same issue!

 

If ive left someone out or more info is needed just abuse me.

 

Thanks for any help!

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I have a similar issue. When i drive to work in the morning, specifically cold mornings, and i am just driving normally, my temp gauge dips below 1/4.

 

After extended driving it eventually finds it way to solid 1/2 way mark. And stays there.

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thermostat installed correctly?

 

I just replaced mine (and hoses and radiator) due to a leaking radiator. it now heats up within 5min (even on these cold winter mornings that usually left it running like a pig for 20min). Mine would also go back to cold on long downhill stretches.

 

My Thermostat had pretty much zero rubber seal left when I took it out.

 

the factory temp gauge could be wrong, as long as your other two temp gauges are indicating normal operating temps then i cant see why you'd worry.

 

aircon probably needs to be regassed.

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Thats the thing though, its not even related to the cold weather...i had the exact same issue on the 30+ degree days in summer. Thermostat was installed by the mechanic so hopefully it was put in right haha. Even if the stock gauge was wrong i still have two other sources telling me its dropping a difference of 35 degrees when going down a hill! Thanks for the input Varvs.

 

aircon probably needs to be regassed.

 

Yeah, just thought maybe it might a related cause

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Sorry if i wasn't clear, there are two sensors i'm getting readings from...the stock location and the top radiator hose. They both read the same temperature (2-3) degrees apart.

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If I were you, I'd take a few minutes to check the seating and orientation of the thermostat. I had a similar problem and it ended up being that the thermostat had dropped out of it's seat when the front housing was being installed (My own fault dammit). At the least, checking it will rule it out. Cooling systems are pretty basic so there can't be too much to it mate.

 

- Lance

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Have you noticed a lack of pressure in the coolant system when the car is running? (i.e can you easily squeeze the top radiator hose)

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If I were you, I'd take a few minutes to check the seating and orientation of the thermostat. I had a similar problem and it ended up being that the thermostat had dropped out of it's seat when the front housing was being installed (My own fault dammit). At the least, checking it will rule it out. Cooling systems are pretty basic so there can't be too much to it mate.

 

- Lance

 

and when you do this ^ do not overtighten the god damn bolts

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yeah it could be that. I used a tiny bit of silicone sealant to hold mine in place while I reassembled it all.

 

EDIT: i should clarify that I put the sealant all over the port on the engine, with enough sealant to hold the thermostat while I reassembled.

 

Also, how tight is too tight for the bolts? i just did them up hand-tight because I dont have a torque wrench

Edited by Varvs

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i just used spit to hold mine in while i put the housing on. Monkey that did mine prior cracked the housing so i replaced it and I just did mine up to normal tight so doesnt come loose

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I had the front of my car jacked up when I did mine. The engine was tilted back enough that the thermostat just sat where I put it.

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Thanks

yeah it could be that. I used a tiny bit of silicone sealant to hold mine in place while I reassembled it all.

 

EDIT: i should clarify that I put the sealant all over the port on the engine, with enough sealant to hold the thermostat while I reassembled.

 

Also, how tight is too tight for the bolts? i just did them up hand-tight because I dont have a torque wrench

 

thats a good idea, ill have a look

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by hot air do u mean literally hot or room temp?

 

heater could be stuck on => coolant going through heater core

Edited by Skepticism

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I noticed my Evo 5 doing that for a while, probably 2-3 months, then one day it overheated and I found it was the thermostat that just died. Probably best to swap it out!

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