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2G Appropriate coolant temperature? Is there something wrong with my coolant system?

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randman2011

10+ Year Contributor
552
282
Feb 26, 2012
Indianapolis, Indiana
What is an appropriate coolant temperature for typical DD operation? The internet throws out numbers between 190 and 215F for city/highway driving. My GSX will get to 170 very quickly but can take 10 minutes or more to get from 170 to 175 and if I drive it long enough, when it hits 190 it will start releasing pressure. It will have a faint smell of burning coolant and the overflow bottle will be hot. Megasquirt has the DSM temp sensor calibration included but I'm not sure if the numbers are a SW problem or a hardware problem. I've ordered a new radiator cap since I'm sure it's beyond its expected life and I've dropped the fan trigger point to 175-185 with hysteresis as a band-aid. But this is not typical, right?

This is the original radiator and it should be replaced as well, but with the one fan on I can keep temperatures below 175 so it is at least working for now.
 
Do you think it's possible your temp scale is off by 10-15F on the lower side? Reaching 170 quick then needing the 10ish minutes to go to 175 don't sound normal UNLESS you're using the lower temp thermostat. If your software is reporting 10-15F lower than actual, then that would mean your *actual* temps are right in the factory ballpark, 185-192F. Then at 192F it should pretty much hold all things considered. On another Mitsubishi I had Evoscan reporting "Temp Coolant" about 10C lower than actual which threw me off until I realized I wasn't using the "SCALED" option.

In any case, see if you can measure the warmed-up coolant temp to cross reference, and do change the rad cap. Fresh water+coolant is a good idea also if yours is old and contaminated.
 
My guess is you have a very low temp thermostat that keeps the car at a very low temp at first. After a while the heat of the engine and engine bay will overrun, if you will, the low-temp thermostat and the car will then operate at it's next lowest possible temperature.
 
@Kryndon @Vegas Smith I replaced the thermostat when I rebuilt the engine last year and I consciously picked the higher OEM 195 degree thermostat for fuel economy reasons, but who knows. I can test it since I have a fancy new liquid thermometer for brewing.

I keep forgetting to pay attention to the normal cruise temperature so I will keep an eye on that next time I take the car out. I'm only ever paying attention to warmup (175* is when it starts autotuning VE tables) and overheating for obvious reasons.
 
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Is there a problem with the cooling system then? Or were you just curious what other people's temps were? Temps should be roughly 200-210 give or take some degrees. It's not set in stone because everyone has different setups.
 
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I saw a graph once of how the friction of the rings against the cylinder walls goes down dramatically as the temp gets over 180F. Wear would therefore also be much reduced, which is nice on a dd. For the price of a new gasket you can take out your thermostat and check it in your kitchen. Pot of hot water on the stove and another reference thermometer. You can calibrate the reference thermometer when the water boils, which is quite close to the range you're trying to measure (so good calibration point). A grilling thermometer or candy thermometer should be fine. Don't get caught by anyone else who frequents the kitchen; could be trouble.

For the price of a new gasket and thermostat, you could just pop in a new one of suitable set-point (OEM is higher; like 195F, most aftermarket "performance" are 180F) and see how that goes. If you don't have detonation when driving briskly, then you don't likely need the colder t-stat. The warmer temp may even help drivability and economy, and reduce emissions in normal round-town stuff and highway cruising. If you get occassional knocking, then likely try to keep it as cool as you can. Still seems like your current sensor or computer are suspect, though.
 
I'm asking if there might be a problem with the coolant system that I should be investigating because it is sufficient for my current driving in the current weather but it doesn't seem right.

Despite the coolant smells and overflow bottle being hot after drives, I have not had to add any coolant beyond topping off the overflow bottle once. It has always been full at the radiator cap. Fans are off when the car is above a threshold speed that I think is either 35 or 40 mph and I don't have any problems when the car is moving. They cycle on and off slowly when just idling, no more frequently than any other car that I own.

Radiator cap arrived today and has been installed but I haven't driven it yet.
 
There are a ton of steps to do in order to check for a properly maintained and sealed system that I need to type out. You need a cooling system pressure tester. Verify that the system maintains 15psi for at least 30 minutes but I do longer. Now get a vacuum filler. That will essentially get rid of the air in the system. Start it up and let it idle to operating temperature. Almost always the center of the temp gauge. At that point the fans should come on maintains that temp. I hope that helps a little.
 
The new radiator cap and adjusted fan thresholds have definitely helped. The only remaining thing to figure out is the factory gauge. I don't ever see temperatures above 198 degrees (it's not hot here yet and I'm not using AC) but the factory temp gauge will display 2/3 to 3/4 sometimes. I feel like at this point I should just replace the gauge sensor on the thermostat housing and hope that fixes it, since everything seems to be operating normally otherwise.
 
The new radiator cap and adjusted fan thresholds have definitely helped. The only remaining thing to figure out is the factory gauge. I don't ever see temperatures above 198 degrees (it's not hot here yet and I'm not using AC) but the factory temp gauge will display 2/3 to 3/4 sometimes. I feel like at this point I should just replace the gauge sensor on the thermostat housing and hope that fixes it, since everything seems to be operating normally otherwise.
My factory gauge sits dead in the middle (1/2 way up the gauge) from ~180F to 213F, only after 216F does it start to creep upwards and it does it quite quickly. I have a spare set of aftermarket temp sensors and I don't recall them being expensive. The service manual has a resistance test for the gauge sensor so you could try that before buying a new sensor.

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