[v8volvo]

You can also adapt a sandwich plate from an earlier gasser Volvo turbo that allows you to mount an external air-to-oil cooler. Several theoretical advantages to this, including reduced heat rejection to the cooling system when the oil is hot and increased coolant flow thru the rad. (I say theoretical because nobody [to my knowledge] has attempted to specifically isolate and quantify the effects of those changes on cooling performance so far, although anecdotally, the last car I did this to went up I-70 from Denver on a hot day with foot to the floor and temp gauge didn't move -- a fairly difficult trick for these units usually, but that car had a fresh rad and other work as well.)

The gasser oil-air setup requires using the threaded nipple from the gasser motor in the diesel's oil filter mount extension in order to make the pieces fit together, since the coolant-oil sandwich plate from the diesel is thicker, and then you need custom hoses and you have to mount the cooler matrix somewhere. And the other issue with the gasser sandwich plate is that it incorporates a thermostat that fails in the cold position, in which case the cooler is bypassed and the setup becomes functionally useless... I just disabled the tstat on that particular car and set it up for full flow all the time, since the car was heading to live in TX, but in a cooler climate you'd want to have some kind of thermostatic control over oil temp rather than running max cooling all the time. The oil-water exchanger is nice in that sense, despite its (relatively slight) risks. They're the same as what's used on all kinds of different VWs and available brand new for cheap if it's really what's wrong. Or retrofit something nicer if you're inspired.

As Fridgewagon said, though, the truth is that headgaskets in these motors have a higher failure rate than the oil cooler sandwiches do. If you pull the cooler off, pressure-test it before you conclude that it's the cause of your issue. If there's oil in the water, better odds that you'll be needing to have the head off in the end.