Having checked the oil in my R53, I've noticed that the engine coolant is mixing with the engine oil.

I've just done a comp test which showed 175/169/176/179 psi across the cylinders. However, I've noticed that the temp on the scangauge shot up to 120ish deg c whilst the in car temp gauge read @ 1/4 also the engine fan didn't come on.

My current thinking is that the headgasket is ok but the oil cooler may be the problem and the temp issue may be down to gunk in the hoses causing local hotspots.

What does everyone think?

BTW - I cant see any traces of oil in the water but had to refill the header tank with @600ml of water. The car hasn't overheated and when warm, the incar temp gauge doesn't shift from the middle.

 

Two years ago I had a similar problem. First of all I had a mysterious disappearance of coolant. Could not see the leak anywhere, and watched my oil constantly. I just continualy topped up my overflow tank...it needed it approx. half the tank every two to three weeks.
One day I was sitting at a drive-thru waiting for my coffee...and my temp gauge suddenly just took off. As soon as I started driving, the temp went back down, but the fan never kicked on. Now bear with me, because there were a bunch of inter-related things going on...
Next fill up, checked the oil, and it looked muddy...aghhhh, thought I had blown the head gasket or worse. Not the case.
I drove the car home over a break (I am at grad school 600+ miles from home). Totally flipping a gasket myself I convinced my husband (who is a certified-maybe certifiable-mechanic) to tear into it, and find out what was going on. At the same time I wanted to get to the source of the ticking in my engine which had started out sounding like an idler on the front of the motor, and had gotten louder since the coffee incident.
He started with an overall inspection which revealed that the wonderful Idaho roads (with all the construction) had filled my power steering fan with enough crap that it had seized...blowing the breaker to not only the PWST fan itself, but also the fan that cools the engine. (There is a service bulletin on this issue of both fans being routed to the same fuse).
Now for the gunk in the engine. Ran a compression test, everything right where it should be...turns out that the relatively short trips I make at school was making the synthetic oil in my engine look like it had water in it. It didnt...but still the coolant was going somewhere...
Look for source of ticking sound. Not on the front of the motor, as it sounded like...it was on the back of the supercharger. The housing that contains the gears that drive the waterpump...shot. When the supercharger was pulled off, it revealed the source of the coolant disappearing...the o-ring between the water pump and the block was shot, you could see the stain running down the block clear as day.
Cost of new PWST fan.....$50.00 (from a MINI junk yard in Sacramento)
Cost of new oil and filer.....$32.00
Cost of newish-low mile supercharger.....$400.00
Cost of new thermostat, o-ring, belt, coolant......$100.00
Cost of labor.....10 1 liter bottles of Pepsi and 3 packs of cigarettes .
Making me stop whining that Klaus was dead, and I couldnt go on...Priceless! (As is the ear to ear grin-cant put a price on that).

I know I went on and on, but you know there were several 'little' things that added up to what I thought was going to be the end of the world. I think your problem might be related...just without the supercharger problem. But you know, without pulling that off the car, we may not have come across the source of the leak. I was certain that it had to be disappearing into my oil somehow, which was backed by the murky looking oil. That was all 15-20,000 miles ago, and I have not had a problem since. I also always that my car gets up to operating temp with the short drives, and the oil has never gotten that way since.
Best of luck to you, I hope its something really simple....and sorry about the book!