I have an issue with my coolant gauge spiking hot at the beginning of a drive and then stabilizing at hotter than normal temps the rest of the drive (about 1-2 notches above horizontal). Some history:
The issue began a month or so ago and I don’t recall anything happening that could have triggered it. It started with it idling fine, but after several minutes, the temps would start to rise to several notches above normal, and then fall back to normal (2-3 notches below horizontal) for the rest of the day regardless of how much the car is driven or rested etc. Eventually the temp spike started to occur later, it would only rise soon after the beginning of a drive (no matter how it’s driven) for a few seconds and fall RAPIDLY back to normal temp. I used to think this meant an electrical problem as there was no way coolant temps could drop that quickly, but then I learned that the OEM temp gauge doesn’t show actual temps. It will rapidly rise up when coolant temps exceed a certain point.
My cooling setup was as follows: TRD 1.3 bar rad cap, Koyo aluminum radiator, 10 degree lower temp thermostat, all fan shrouds 100% intact, OEM clutch fan, OEM underbody panel, heater control valve locked open because it’s broken, ISCV and TB coolant passages bypassed, OEM CT26 with factory coolant lines.
Engine setup: Cometic MHG with ARP studs torqued to 95ftlbs. Eagle rods, JE Pistons. Stock head, turbo, injectors, AFM & housing. COP conversion operating in wasted spark like stock. Boost spikes to 14psi max, fuel cut normally hits around 10-12psi.
This setup gave me rock steady temps for almost 2 years.
Motor is healthy as far as I know, latest compression test was after this issue started and it was 175 +/- 1-2 psi across the board with the engine cold. Comp test before that was done a few months before and was performed correctly with motor warmed up and that was 180 +/- 1-2 psi across the board. I am not losing any coolant, there is no boiling when the car is shut off and coolant is not being pushed out of the rad cap or overflow reservoir. Oil is clean, and coolant is free of oiliness. I tested the clutch fan by attempting to stop it with the engine running, and there was strong resistance. My uncle (a Ferrari tech for the Scuderia Corsa GTD team at the time) performed the same test and said it felt fine. I also swapped on a brand new radiator cap set at OEM pressure with zero change.
As such I thought I had a sensor or electrical problem, so this week, I replaced the thermostat with a new OEM temp one as well as brand new ECU temp sender and coolant temp gauge sender. During the burping process, the car ran for a little less than I wanted to since I was low on gas, so only about 5 minutes after getting to operating temp (1-2 notches below horizontal), where it stayed the entire burping process. I made it about two miles from home before the temps shot rapidly up, almost to red (about 1-2 notches below red, much higher than before) for a few seconds before falling back down, but this time much higher than it used to, 1-2 notches above horizontal. I made it to the gas station and back with temps not rising any higher or going any lower. One strange thing to note is that with the key in the ‘on’ position, the temp gauge would read normal (1-2 notches below horizontal) and would only rise to hot when the car was started. I performed two more test drives that night, each time the temps would spike almost to red a couple minutes after driving for a few seconds before falling rapidly back to 1-2 notches above horizontal. Note the difference where before it would only spike once a day on the first drive.
So I am stumped and have no idea what could be causing this issue. Someone suggested a clogged radiator. Bad clutch fan was already addressed and tested. Water pump was suggested as well, but the symptoms for that tend to be more obvious. Some think I might just have a fucked up coolant temp gauge, I have no way to test that. I will be performing a lengthy burping tomorrow morning (30+ minutes with the nose to the sky) and will report back, but I don't envision this helping as I already tried a lengthy burping to fix it when the issue first started. I am open to suggestions and anyone that has personal experience with similar issues.
Thanks for reading.
The issue began a month or so ago and I don’t recall anything happening that could have triggered it. It started with it idling fine, but after several minutes, the temps would start to rise to several notches above normal, and then fall back to normal (2-3 notches below horizontal) for the rest of the day regardless of how much the car is driven or rested etc. Eventually the temp spike started to occur later, it would only rise soon after the beginning of a drive (no matter how it’s driven) for a few seconds and fall RAPIDLY back to normal temp. I used to think this meant an electrical problem as there was no way coolant temps could drop that quickly, but then I learned that the OEM temp gauge doesn’t show actual temps. It will rapidly rise up when coolant temps exceed a certain point.
My cooling setup was as follows: TRD 1.3 bar rad cap, Koyo aluminum radiator, 10 degree lower temp thermostat, all fan shrouds 100% intact, OEM clutch fan, OEM underbody panel, heater control valve locked open because it’s broken, ISCV and TB coolant passages bypassed, OEM CT26 with factory coolant lines.
Engine setup: Cometic MHG with ARP studs torqued to 95ftlbs. Eagle rods, JE Pistons. Stock head, turbo, injectors, AFM & housing. COP conversion operating in wasted spark like stock. Boost spikes to 14psi max, fuel cut normally hits around 10-12psi.
This setup gave me rock steady temps for almost 2 years.
Motor is healthy as far as I know, latest compression test was after this issue started and it was 175 +/- 1-2 psi across the board with the engine cold. Comp test before that was done a few months before and was performed correctly with motor warmed up and that was 180 +/- 1-2 psi across the board. I am not losing any coolant, there is no boiling when the car is shut off and coolant is not being pushed out of the rad cap or overflow reservoir. Oil is clean, and coolant is free of oiliness. I tested the clutch fan by attempting to stop it with the engine running, and there was strong resistance. My uncle (a Ferrari tech for the Scuderia Corsa GTD team at the time) performed the same test and said it felt fine. I also swapped on a brand new radiator cap set at OEM pressure with zero change.
As such I thought I had a sensor or electrical problem, so this week, I replaced the thermostat with a new OEM temp one as well as brand new ECU temp sender and coolant temp gauge sender. During the burping process, the car ran for a little less than I wanted to since I was low on gas, so only about 5 minutes after getting to operating temp (1-2 notches below horizontal), where it stayed the entire burping process. I made it about two miles from home before the temps shot rapidly up, almost to red (about 1-2 notches below red, much higher than before) for a few seconds before falling back down, but this time much higher than it used to, 1-2 notches above horizontal. I made it to the gas station and back with temps not rising any higher or going any lower. One strange thing to note is that with the key in the ‘on’ position, the temp gauge would read normal (1-2 notches below horizontal) and would only rise to hot when the car was started. I performed two more test drives that night, each time the temps would spike almost to red a couple minutes after driving for a few seconds before falling rapidly back to 1-2 notches above horizontal. Note the difference where before it would only spike once a day on the first drive.
So I am stumped and have no idea what could be causing this issue. Someone suggested a clogged radiator. Bad clutch fan was already addressed and tested. Water pump was suggested as well, but the symptoms for that tend to be more obvious. Some think I might just have a fucked up coolant temp gauge, I have no way to test that. I will be performing a lengthy burping tomorrow morning (30+ minutes with the nose to the sky) and will report back, but I don't envision this helping as I already tried a lengthy burping to fix it when the issue first started. I am open to suggestions and anyone that has personal experience with similar issues.
Thanks for reading.
