Hi everyone,

I have a general question regarding the charge air coolers on the SC XJR and their exact workings.

I have never paid too close attention to different temperatures in the engine bay but yesterday I checked the two SC intercoolers by accident. The car has been driven for 20min on the highway, including some WOT overtakes near the end. In my garage, the car idled for some time, engine was at operating temp as always (92C (198F) on the dash / 92C (198F) on the OBD reader), meaning the thermostat is open (is also new) and all directions near the thermostat housing are hot. Basically the whole engine is hot to the touch but the two SC intrercoolers are cold. Not "colder than the rest" - genuinely cold. Also the four hoses connected to the SC intercoolers are only mild warm, compared to the hot rest. Car has full power and performs great.

Today I did drive a bit further and the two SC intercoolers are definetely warmer than yesterday, yet much colder than the rest. Which is their correct function I assume.

Can anyone share some light on the two loops of engine coolant? Especially how the SC loop operates.

Thank you!

 

This should give you an idea of it's operation, I've had condensation form on them some days they work that well. For our friends in hot places, they've fitted killer-chiller kits that utilize the air conditioning to help cool the loop. Having a larger intercooler radiator also helps, but once the whole system is heat soaked it all becomes the same temperature, that's when the ECU pulls timing and it feels down on power (very hot days and heavy use).

 

Interesting, as when I got my XJR it'd massively lose power after about 30miles until it'd gone cold again. I eventually tracked down to a blown fuse for the charge cooler pump. Can't say I've ever thought to check their temps after driving the car since, but I do know that part of the bonnet is the last 'directly over engine' bit to defrost, not the first like it was when I first got the car.

 

Yeah this sort of thing is absolutely normal. If anything, if your charge coolers AREN'T cold after some normal calm driving, that's when you've got some problems.
I had a nice image from the x308 tech docs on this, I may try and find it later. Basically the two system loops flow independently, but they are connected to each other for fluid exchange and sharing a common supply I guess.

 

Of course the intercoolers will be rather cold in the winter. If the ambient air temperature is around 0C, I think that the intake air will be cooling the collant in the intercoolers and not the other way round which is the intended purpose of the intercoolers. Check the intercooler temperature in the summer, on a hot day, and after some spirited driving.

 

Amazing Sean! That helps a lot, thank you. I actually was not aware that our cars have a separate radiator for the charged air. Is it near the engine oil cooler up front?

 

Ok, that makes sense. Thank you!

So upgrading the SC pump to the stronger Bosch version is the way to improve the system I assume.

 

Just to give you a few numbers: I was driving through the Arizona desert on a hot afternoon, outside temp was 111F, engine coolant was 204F, intake air was 91F. I'm running the big intercooler radiator and the Bosch pump.