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Discussion Starter #1
I believe I need a new thermostat. Not sure which one so I'll replace both but during WOT my temps drop from 190ish (normal operating temp) all the way down to 150ish and then when I let off it goes back up.

I've seen all types of things people are doing:
SR20 170* and Chevy 195*
Mishimoto both 177*
97 Altima 170* both
Gutting upper

From what I've read, you need to have at least a 20 degree difference between the 2 thermostats so it makes me wonder about the people who run the same temp on both or gutting the top.

I don't track the car but I do drive it hard. It has a Koyo and 2 Spal fans and I've never had any issues overheating, so I'm wondering if it really is that much better to not use the stock temp thermostats if it's not being tracked. I don't have any way to shave the sr20 one down so that one's not much of an option.
 

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Don't gut our you will throw a code especially when cold, i ran same upper and lower temp before for several years with no issues after a head gasket failure iirc.

Pick your poison but if it's running fine and the temp is dropping like that is leave it alone till summer and see what the temps are then.
 

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Discussion Starter #3 (Edited)
Shouldn't I still replace them with at least the stock temp ones though? I thought if it drops like that it means the thermostat is getting stuck open.

It just started happening recently which is why I think something is wrong
 

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You are fine, should be a temp drop when the t-stat opens, I just don't know by how much but as it's cold out in sure that may explain part of it, maybe someone else may have a better idea as I don't remember any of the technical cooling system stuff.
 

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Discussion Starter #5
The cold weather would make it drop that much? I'll try to do some pulls and screen record the Torque app and upload it
 

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I would replace both with oem from nissan to rule it out. Then double check. Sounds like its flowing too fast, which can cause issues because the engine is not up to operating temp.

In my exp, cold air doesnt effect it like that
 

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Discussion Starter #7
Would oem be better than the sr20 and chevy ones? Has the theory that the oem thermostats are too high which lead to head gasket failure been proven?
Here's a video of me pulling on to a freeway after the car has gotten up to temp. The Torquesync app would not work for me so I had to combine the subtitle (text) with the video so it only shows as text instead of gauges. Also, not sure why the temperature shows as Fahrenheit with Celsius values but you can see the temperature fluctuating in relation to throttle and rpm
 

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Been running Mishimoto thermostats I'm my 2012 Altima for bout a year, no problems at all.
 

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Dam Ive never seen that kind of fluctuation before of 30*C. Very odd. I would still replace with oem thermos and temp sensor and see what happens. Or mishimoto if you want a colder stat.

I havenet believed that theory. This car is meant to get hot fast in the head and block for emissions reasons because of no egr. You also want the engine to be at operating temp quickly.
 

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Discussion Starter #10
Yeah it's pretty weird. Alright I'll just get the oem ones then and I'll do a flush while I'm at it since its time for one anyways. Do I need to get the oem sensor too or would a stant one be fine?
And do you have the oem thermostats in your car?
 

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Oem yes currently. Have mishimotos for the other block but might go oem just cuz. Personally I would never gut them or anything.
 

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Discussion Starter #12
I just got some oem ones. Hopefully I'll have time to put them in tomorrow as well as flush everything out. I'll report back here once I do and go for a test run.
 

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Discussion Starter #13
Looks like the previous owner gutted their upper thermostat
172732


Put in the oem ones for upper and lower. Lower had an aftermarket one made from China. Flushed the system and did a bunch of pulls on the freeway and it stayed in between 179 and 185 the whole time. No fluctuating!
 

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Would not have expected that, good info for sure for future use.
 
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Yup coolant was flowing too fast. Cool side effects from doing that. I think the lower one would open and close all the time allowing coolant to sit in the rad until it was warm enough to open, then shut as the cold coolant flows by. That kinda proves they work together in this engine.
 
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