Ok, I'll add my tuppence..! We've been here before, but what the heck, its a slow weekend.
When I refurbed my +2, I junked the Ambient air temp gauge and fitted a similar looking oil temp gauge, with the sensor in the sump plug. I note that the oil takes a good while to get to around 60-90 DegC (5-10 miles), and under normal road conditions runs up to around 90-110. Motorways, at a steady 70mph+ in Summer (or at least what passes for it in the UK) cause the oil temp to climb over 120 or more. So far so good. My first long distance foray down the autobahns to the Alps and beyond saw the oil temp hit the max stop of 140+ on the guage anytime we went up serious gradients, or at serious speed. I was running Millers 20-60 synth, so the oil was running at close to its limit for long periods. When I got home, I checked the accuracy of the gauge with 'tell tales' on the sump and oil filter housing. These are stick on temperature sensitive strips that change colour irreversibly when a temp is exceeded.
http://temperature-indicators.co.uk/aca ... abels.htmlI am satisfied that the gauge is accurate to +/- 5DegC, which is still a wide range. For my next trip I fitted an oil cooler in exactly the way described above. Result, the oil temp stabilises at around 90-110 in the UK, on most runs I have undertaken. On a two week haul in Italy last summer, in what even the locals called a seriously hot summer, blatting down the Autostrada and up the mountains, the oil temp got up to 130, tops, never going near the Max-out zone. The gauge usually sat in the 90-110 zone, in normal running, even in the extreme heat. Back home and over last winter, I noted the oil temp was quite sluggish to warm up, so at the scheduled oil change, I removed the cooler. This summer, the oil temp rise is back to the pre oil cooler behaviour. Note that at all times, even when the oil temp was maxed out, the water temp was within limits - mid gauge.
This experience tells me that without any regulation, the oil has no real mechanism to lose excess heat when the engine is working hard. Not hard to imagine given the humble origin of the block which wasn't designed with this in mind. The cooler & built in thermostat was working, evidenced by the normal heat up to 90C, and hunting around this point until it settled down into an equilibrium. For extreme stress, the 13 row cooler is just about adequate, evidenced by the rise to 130+ under extreme conditions, but no further.
What are the implications for all this?
Under normal UK conditions, you probably don't
need an oil cooler and in winter it is a nuisance.
Heat transfer from over-heated oil to the water side is not going to be significant, given the small delta T, and limited surface area. An oil cooler, even in the hottest conditions has both a massive delta T and surface area.
Under high stress - 120C+ - you must use a synthetic oil and even then it is running close to its limit.
Is the peak thermal stress under hard use responsible for accelerated engine wear seen in pre synthetic oil days?
Fitting an oil cooler is desirable if you drive at anything like 'normal' modern motorway speeds in hot countries, but is worth removing for autumn/winter use in temperate countries.
Anyone who states you never need an oil cooler in a road going Elan probably has a financial interest in rebuilding engines.
The most important thing for prolonging the life of an engine is clean oil, at the correct temperature. The further away from ideal, the more quickly engine wear occurs. Clean oil is easy to maintain with regular oil & filter changes, but without knowing the temperature of your engine oil, with some degree of accuracy, you are running blind. Are you feeling lucky?!
Now, all I have to do to scare myself again is fit sensors in the gearbox and diff housing with a selector switch in the cabin! Ignorance is bliss, but accurate data is better.
Jeremy
PS once the cooler has been fitted, it is a 20 minute job to remove, or put back on, when you change the oil & filter.