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I did a bunch of work on my Maxima which included new heater hoses, thermostat and coolant temp sensors. I put everything back together and proceeded to bleed the cooling system by letting it warm up on an incline with the radiator cap off. It bled some air as expected near when the thermostat should open (180F), I closed it up and took it for a drive. For some reason the coolant temp stays between 204-210F instead of the 190-something like it's supposed to. This causes the radiator fans to run all the time. One thing I've noticed is that the top of the radiator is hot, but the lower half of radiator and lower hose is cool to the touch, even after a long drive, or idling for a long time. I don't see any movement of the coolant looking through the fill port. The temp never goes above 210F, no matter how I drive it, or how long it idles.
I tried a new thermostat, and even tested both thermostats by heating them up in water with a thermometer-- both began to open at the same time, around 180F and were fully open by 200F. Tried the old coolant temp sensor, I'm still getting the same readings, I'm measuring temp via a scan tool. When the temp is at 210, the needle on the gauge is slightly past half, just like I'd expect it to be. I'm pretty sure the engine ran a little hot before I did this work, because the cooling fans would run often even when I wasn't sitting in traffic, but the gauge stayed around the half mark, so I never bothered to get a readout from the ECU/scan tool until now.
Anyone else have any trouble like this? The water pump should be good, I replaced it around 220k miles, I've got 280k on it now. Radiator is an aftermarket unit that was replaced a few years ago. Not sure if this is a symptom of a bad radiator, air in system, or what's going on here. Hoping someone else has had similar problems and could point me in the right direction. I should mention that I've pressure tested the system, no leaks. Open to input / suggestions, thanks in advance.
I did a bunch of work on my Maxima which included new heater hoses, thermostat and coolant temp sensors. I put everything back together and proceeded to bleed the cooling system by letting it warm up on an incline with the radiator cap off. It bled some air as expected near when the thermostat should open (180F), I closed it up and took it for a drive. For some reason the coolant temp stays between 204-210F instead of the 190-something like it's supposed to. This causes the radiator fans to run all the time. One thing I've noticed is that the top of the radiator is hot, but the lower half of radiator and lower hose is cool to the touch, even after a long drive, or idling for a long time. I don't see any movement of the coolant looking through the fill port. The temp never goes above 210F, no matter how I drive it, or how long it idles.
I tried a new thermostat, and even tested both thermostats by heating them up in water with a thermometer-- both began to open at the same time, around 180F and were fully open by 200F. Tried the old coolant temp sensor, I'm still getting the same readings, I'm measuring temp via a scan tool. When the temp is at 210, the needle on the gauge is slightly past half, just like I'd expect it to be. I'm pretty sure the engine ran a little hot before I did this work, because the cooling fans would run often even when I wasn't sitting in traffic, but the gauge stayed around the half mark, so I never bothered to get a readout from the ECU/scan tool until now.
Anyone else have any trouble like this? The water pump should be good, I replaced it around 220k miles, I've got 280k on it now. Radiator is an aftermarket unit that was replaced a few years ago. Not sure if this is a symptom of a bad radiator, air in system, or what's going on here. Hoping someone else has had similar problems and could point me in the right direction. I should mention that I've pressure tested the system, no leaks. Open to input / suggestions, thanks in advance.
How long did you bleed? I usually bleed for over 30 or 45 minutes. The air bubble can be stubborn. I use one of those special coolant funnels they sell on Amazon with (yellow color) with matching connectors. I already recouped money's worth - it's really useful.
I let the funnel sit on radiator with some coolant in it and let the air bleed for a while. Never had over heating issue.
On your case, I doubt it's the thermostat. It's probably air bubble somewhere. Or, the radiator is bad. I also replaced mine with a Denso unit (rockauto or amazon) three winters ago.
Did you change the thermostat, or the thermostat with housing? If thermostat only, then IIRC, the thermostat can be installed two ways. Only one way is correct with the tiny little opening facing up. OEM or aftermarket?
How is the condition of your radiator cap? Have you tested it?
Finally got this figured out. It was the thermostat.
To recap, the car had always run a bit hot, like around 205F when it should be around 190F. Since I was replacing a bunch of hoses and doing other service, I figured I'd try to fix the running hot issue. I replaced the thermostat, bought a Motorad brand from Rock Auto. Exhibited the exact same symptoms, cooling fans would run all the time, bottom of radiator cold, engine at 205-210F constantly. I went to Autozone and bought their Duralast brand thermostat, but it too, was a Motorad in a Duralast box. Tried it, same problem. The Motorad thermostat comes as the thermostat element built into a housing.
I decided to order an OEM thermostat from the Nissan dealer and that fixed the problem. The aftermarket and OEM thermostat look very different, I can conclude that the aftermarket thermostat has a design defect or they missed some crucial detail when copying the OEM thermostat.
I've attached some photos comparing the two, aftermarket on left, OEM on right. Most obvious difference is that the Motorad thermostat is missing a little baffle plate that's present on the OEM one; I assume this must serve a purpose.
Car runs 185F on the nose now, until you hit slow traffic or stop then it will creep up slowly to 203F until the cooling fan kicks on. Within seconds it's back down to around 195F. Just like it should be. If anyone happens to have one of these Motorad thermostats in their car, throw that sucka in the trash!!! Who knows how long I had that crappy thermostat in the car, I didn't really notice the running hot issue until I plugged a scanner into the car, because even at 205F running temperature, the gauge still sits around half, but the cooling fans will never shut off. I just always thought the cooling fans were sensitive
Assuming in your last two pictures, you have the thermostat housing in the same orientation, the bleeder valve thingy is in the wrong spot. Thermostat would need to be flipped 180 degrees. This may be the cause of your issues.
03-26-2021, 07:36 PM
