need heelp with overheating car. tried everything

[metric310]

Hi. I have an 06 M45 with 94K miles. it has been overheating lately and I cant figure out why. I have replaced the water pump, thermostat, radiator cap, water control valve, they checked the radiator and said it was good, just had a block test done to check the head gasket while it was running super hot and bubbling in the reservoir and there wasn't any emissions in the coolant. it only seems to overheat when the AC is running, and it takes a bit till it starts to overheat, maybe 40 mins??? then it wont come back down..... any help would be appreciated....

[DeanM45]

Is the electric fan running?
Faulty fan motor(s)
Faulty Fan Control (located on the fan assembly)

[metric310]

fan sensor was also replaced, and the fans do trun on...

[DeanM45]

OK,
1) they should be able to set the fan duty cycle to 100% using a scan tool to see if the fans come on full. When the car is hot the fans should be LOUD as they should have 100% duty cycle.
2) With the car cold, take the radiator cap (not the overflow) off and start the car. See any bubbles? If so, cracked head, block or head gasket
3) When the car is running the face of the radiator should be warm across the face. Difficult to do but it can be done by removing the brackets and pushing the radiator slightly towards the motor to fit your hand on the front of the radiator. If you feel any cold spots that means there is a blockage in the radiator.

Since it only overheats with the a/c on it is more than likely the fan/fan control circuit or the radiator.

You said that the mechanic checked "everything" but obviously not or the car would not be overheating. If you are driving and the car starts to overheat put the heater on full and if the temp drops fast then it is the radiator or fans. However, do not run the car hot for any length of time or you WILL warp the heads.

[KayhanW]

Remember gang, the mighty VK45 comes from factory with NOT an electric fan like most cars but a Hydraulic fan so please do get it checked out for Fan Clutch having an early failure.....Like them Jaguars, to keep the motor quiet while idling, hydraulic fan has been used on your motor. There is a canister that contains the Hydraulic oil so make sure you have enough fluid in there as it maybe seeping out if not leaking?

[DeanM45]

No. 2006+ M45s have electric fans.
Pre 2006 M45 and Q45 have hydraulic

[KayhanW]

Ahh...thanks for the update...I had not known about the tuned down VK45 in the Nissan Fuga.

[DeanM45]

tuned down VK45 in the Nissan Fuga.

L-O-L!

[KayhanW]

Well i guess on papers they post it at 2006 - 2010 335Hp vs 340Hp 2003 - 2004 which even had an advantage on the power to weight ratio on the vehicle even if it was by a small amount....

[KayhanW]

tuned down VK45 in the Nissan Fuga.

L-O-L!

That is pretty cool how the awesome fuel mileage on the highway you pulled off with your M as I believe the best i had gotten was about 22.5 or so having a toddler & wife in my car as I typically do not do much out of town road trips on mine.

[Larz]

If you akready did this bit, just ignore.
When I had my coolant system flushed and refilled, I was driving home and bout 1 mile later, the air con stopped blowing and the temp gauge was pinned to the max. I called the shop and they told me to drive it back and ignore the temp gauge - they told me it was an error in the filling process. Turns out, there was some air left in the system and when the air pocket went past the thermostat, it got stuck and the temp gauge went bonkers. They re-flushed and re- refilled the system and all was fine after that.