On this particular car, the problem is likely the oil cooler. Check at the oil filter housing. I think that your car has a sheet metal oil cooler mounted on the oil fitler extension housing just forward of the oil filter. It should have two water lines attached. These have a history of developing leaks - it may simply need to be replaced. You can remove it and perform a pressure test on it. If you have the older style cooler, there will be a cast piece there with OIL lines vice the sheet metal piece with WATER lines. The earlier cooler adapters have no water interface so cannot leak water, but do develop oil leaks from worn O-rings.

Steve

Thanks. I passed your advice on and we found it!

The problem turns out to be the transmission cooler, which for my 740 is apparently located IN the radiator! I and the friendly neighbourhood mechanic have never heard of that before. Perhaps it is only on Oz spec cars, where the conditions are hotter?

From what we see of the radiator, the cooler has sprung a pin-hole leak (determined by pressure testing). This forced transmission fluid into the radiator, and over to the expansion bottle where I spotted it.

But even when I checked the transmission fluid it did not show any lower level. I suppose it is hard to see when it is hot on a dip stick.

Non-reparable, so a new radiator ($A300!). A bit annoying @126,000 kms.

What will those guys in Goteborg think of next?

Thanks for your advice.

Chris H.