I was driving some longer trip yesterday and I noticed that my coolant temperature is fluctating according to the driving style. It was relatively cold (10C=50F) and raining.

When I drive normally, i.e. little harder, not pushing it to the limit, just cruising with middle throttle, the temp gauge sits one bar below the center, which seems normal to me:


When there was some traffic that was constantly moving, I just drove in 5th gear at 2000-3000rpm with minimum throttle, the temp gauge was sitting 1 bar lower than normal:

When I push the gas pedal little more, the temp gauge moves back to normal in a minute or so, actually it moves between these two positions according to the gas pedal (with some delay).

When I was driving downhill and braking with my engine for about 1 minute (no throttle and in a gear), the gauge showed 2 bars lower than normal:


Is my thermostat faulty?

 

Or the temp sensor. Check that first. Is it always acting the same? Then it's more likely the thermostat.

 

Yes, it always acts the same way.

With a faulty sensor, would the gauge move this way? I mean, the indicated temperature corresponds with the suggested coolant temperature with a faulty thermostat.

With a faulty sensor - wouldn't the gauge flucuate randomly?

 

What parts in the cooling system are different then stock?, lets start with that first.

 

Funny that I see this today, becuase I had the EXACT same problem last night. I have had the problem for a while...but I was going downhill and it was cold outside and my temp did drop as low as his lowest example.

The entire cooling system is stock, nothing has been modified. I do notice the temperature fluctuation fairly frequently.

J N

 

I have a friend with the same problem. We replaced the thermostat and thermoswith with a mugen one and the problem is still there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bbasso &raquo;</TD></TR><TR><TD CLASS="quote">What parts in the cooling system are different then stock?, lets start with that first.</TD></TR></TABLE>
everything 100% stock.

 

Now I realize that I can make some simple test - start a cold engine and check the temperature of the radiator. If it gets warm immediately, the thermostat is faulty and not closing fully, right?

 

I've been having the same problem as well. My gauge fluctuate like yours too, but mind jumps between normal temp (1 bar below half) to cold (c) depending on how much throttle I give. If I gas it, the gauge would jump to cold. Could this mean that my thermostat is stuck open? Therefore as I press on the gas it pushes cold colant through the temp sensor? I'm still trying to figure out the problem.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by crx_kid &raquo;</TD></TR><TR><TD CLASS="quote">I've been having the same problem as well. My gauge fluctuate like yours too, but mind jumps between normal temp (1 bar below half) to cold (c) depending on how much throttle I give. If I gas it, the gauge would jump to cold. Could this mean that my thermostat is stuck open? Therefore as I press on the gas it pushes cold colant through the temp sensor? I'm still trying to figure out the problem.</TD></TR></TABLE>

Umm... hmm... any chance that's a blown head gasket? air bubbles in your coolant? Does your coolant reservoir overflow, and does your radiator stay filled with coolant?

-Chris

 

i dont think this is a problem with the thermostat. No matter if the thermostat opens or closes, there is no way the coolant (while the motor has been running) is getting cool enough (even when coasting downhill on a cold night) to let the needle drop that low in the gauge. Im guessing its the sensor or something else.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by petrv &raquo;</TD></TR><TR><TD CLASS="quote">Now I realize that I can make some simple test - start a cold engine and check the temperature of the radiator. If it gets warm immediately, the thermostat is faulty and not closing fully, right?</TD></TR></TABLE>

Actually, if I'm not mistaken, I think it's the opposite. The thermostat usually stays closed at start up to help the engine get up to normal running temperature faster. Once the engine heats up, then it will open up.

I don't think it's the thermostat either. When mine broke, luckily it broke in the open position and never warmed up, but it never fluctuated like what's happening to your car.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiRevn &raquo;</TD></TR><TR><TD CLASS="quote">
I don't think it's the thermostat either. When mine broke, luckily it broke in the open position and never warmed up, but it never fluctuated like what's happening to your car.</TD></TR></TABLE>

Not lucky, modern thermostats are designed to remain in the open position when they malfunction.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HiRevn &raquo;</TD></TR><TR><TD CLASS="quote">Actually, if I'm not mistaken, I think it's the opposite. The thermostat usually stays closed at start up to help the engine get up to normal running temperature faster. Once the engine heats up, then it will open up.</TD></TR></TABLE>

No, he's got it right, maybe you misunderstood. If the thermostat is broken (open always), the thermostat will get warm right away after starting, since lukewarm coolant will flow through it.

If the thermostat was closed (proper position), it will stay bone cold until the thermostat opens.

-Chris

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ccfries &raquo;</TD></TR><TR><TD CLASS="quote">

Umm... hmm... any chance that's a blown head gasket? air bubbles in your coolant? Does your coolant reservoir overflow, and does your radiator stay filled with coolant?

-Chris
</TD></TR></TABLE>

No, the coolant does not over flows and the rad stays filled.

But I drove the car today and I notice that it does it constantly now as I'm driving. Actually, the needle on the temp gauge dives to cold when ever the engine revs past 3500 rpm. If I shift without reving past that, the temp seems to be fine. I've just been driving below 3500. Anything past 4000 and the temp gauge goes to cold! Could it be the temp sensor? If so, shouldn't a check engine light come on?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ccfries &raquo;</TD></TR><TR><TD CLASS="quote">

No, he's got it right, maybe you misunderstood. If the thermostat is broken (open always), the thermostat will get warm right away after starting, since lukewarm coolant will flow through it.

If the thermostat was closed (proper position), it will stay bone cold until the thermostat opens.

-Chris
</TD></TR></TABLE>
Must be radiator.

 

My GSR is doing the same thing - My radiator is only 1 year old. My thought was the t-stat was sticking open allowing the coolant to circulate and therefore stay cool.

Anyone else have any ideas?

 

Test done:

I started my cold engine and watched what happens. The upper hose and gradually also the upper part of the radiator (the plastic on the top) were getting warmer and warmer just from the start. The lower hose stayed cold until about this temp, when the thermostat probably opened fully:



Then the temp stayed at this level (this level is still cold for an ITR), maybe it was going a bit to the colder side, right after the thermostat opened.

What do you think?

 

I think you should invest in an autometer water temp guage to know for sure whats going on.

 

I have the same problem as welll... mine is a 98' what year is yours...

maybe they get screwy after awhile. seems like many people on this thread are having the same problem... i say dont worry about it ... unless it goes down to cold "C"

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mikestypeRR &raquo;</TD></TR><TR><TD CLASS="quote">I have the same problem as welll... mine is a 98' what year is yours... </TD></TR></TABLE>
Mine is also 1998

 

Mine was doing hokey things on my ITR as well. Turns out mine wasn't connected well (after my clutch install). Once I unplugged it, cleaned it (with contact cleaner) and then plugged it back it all the problems vanished.

 

If the radiator gets warm before the temp gauge is up close to the normal (one tick below half) mark, then the thermostat is open prematurely or stuck open.

For the guy whose car cools down when revved, yeah, you need a t-stat as well. Water pump pressure is enough to overwhelm the t-stat when you rev it up, that's why you need a t-stat.

[/Lecture mode on/] Engines that run too cold run too rich. They also don't allow the pistons to fully expand to fill the bores and can eventually wear out cylinder bores... Don't ignore cooling system problems. Running an engine too cool is also bad for it!!! [/lecture mode off/]

 

Hmmm glad I clicked on this thread. I've noticed that when driving my car hard or in stop and go traffic my gauge will sit right on this mark:



If I'm on the interstate driving in cool weather it'll sit just below the same mark, barely a noticable change in position. Do I have a problem?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chris93Si &raquo;</TD></TR><TR><TD CLASS="quote">Hmmm glad I clicked on this thread. I've noticed that when driving my car hard or in stop and go traffic my gauge will sit right on this mark:



If I'm on the interstate driving in cool weather it'll sit just below the same mark, barely a noticable change in position. Do I have a problem?</TD></TR></TABLE>

nope. thats normal.

funny I clicked this thread. same thing started happening to me. I just got back from the stealership and picked up a thermostat and gasket.