Coolant pressure sensor readings

Hi all,

I need some advice, I have just installed a Bosch dual pressure and temp sensor to a Nissan Skyline GTR 32. The motor has been having coooling issues. Tempreatures rise from normal operating tempreature to 95-100C in moderate driving. Since the spike in tempreatures, the vehicle now has a new mishimoto radiator with dual radiator fans, new thermostat and the cooling system has been bled multiple times. We suspect it may be a head gasket and will perform a leak down test soon.

I do have a coolant pressure and have been comparing the logs from when we received the vehicle and after the new radiator , fans and thermostat. I confirmed that the fans ( 2 radiator and 1 condenser fans) are working normally.

As I can see, when the engine coolant system operates normally , the pressure sensor reads between 100kpa to 220kpa and engine temps are much more stable betyween 88-92C with moderate to high loads. Recently, with the spike in coolant temps, the pressure sensor only reads 100-120kpa and the coolant temps rise to 95-100C with normal medium load driving.

Does the lower coolant pressure indicate that the water pump is not working as normal as with higher revs, the coolant pressure does NOT seem to increase and is only at 100-120kpa.

I have attached two log files for the short test that we did.

Apprecaite advice for those who use coolant pressure sensors to monitor the cooling system to advice and share.

Thanks in advance.

Just looked at the logs from my racecar, and the coolant pressure varies based on engine speed, but also on fan activation. When the fans are running, the pressure will drop from a peak of around 180kPa down to 80kPa. i believe that this is due to the contraction of the volume of water in the radiator as it is being cooled going through the area that the fans are providing extra cooling to.

Stephen, thanks for the feedback. That makes sense. coolant pressure should vary with engine speed as the water pump is turned by crank pulley. Higher revs, higher the water pump turns.

However, this past week, the pressure seems to be constant at 100-120kpa even on moderate to high loads compared to the previous logs we had. I suspect it is a failing water pump. I am hoping its the pump and not a head gasket.

The reduced pressure could indicate a leaking coolant system pressure cap. Are you having any coolant expelled into your recovery/catch bottle?

Hi David, Yes the coolant overflows thru the recovery/catch bottle when we shut down the engine (When its hot 95-98C).

We did do a coolant system pressure test by pumping 1.3 bar of air into the system to check for leaks but none so far.