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hi since i've had my defap and remap i've noticed that the oil temp gets much higher when engines under load, going over the servern bridge on the weekend the oil temp was quickly climbing and peaked at about 120c ( i've worked out that the line before 140c is about 126c) before we hit the middle and started to come down the other side, this is only a slight incline and I was travelling at 70mph, the car was loaded with 4 people and a full boot, is this normal? I hate to think how high it would go crossing the pennines on the M62 and what would happen if it did get into the red, the oil was changed about 4000 miles ago but I don't know what oil was put in as it was done by a garage.

What oil have you got in ?

go up a stage perhaps 10w 40


Edit: doh, just re-read, you dont know what oils in,

It definitely depends on how hard it's working and for how long.

Mine will go as low as 90 ish if going really gently and will exceed the vertical even in cold weather if working hard.

Bearing in mind the system is designed to lose heat to the water, (which is near 90 degrees anyway), it follows that the oil must run hotter. I'm guessing that provided it stays well clear of the red, you can't go too far wrong.

(If anyone knows the facts, please comment).

I understood an engine oil's ideal running temp to be 105deg C but it can 'peak' under load. What you described is normal for a fully laden car on an incline; the crank will be under more strain as it hauls the load up the hill transferring heat into the oil.

You may try a more favourable engine speed next time? maybe you were in 5th? in which case it might have been happier in 4th - this will raise the revs and the oil pressure to suit.

Additionally, the re-map will be producing more heat. By modifying the engine's output it would be recommended to double the oil changes. I would recommend Fuchs/Silkolene XTR 10w/40, this is semi synthetic and a very high quality one - this should keep the oil temp in check too.

The thing is if you didn't have an oil temp guage you wouldn't worry about it,my bmw hasn't got an oil temp gauge and when i tow my caravan the oil must get pretty hot but as i don't know i don't worry about it,i stick to regular oil changes and thats all i can do.I had a brand new Volkswagon Transporter for a few days last week and that didn't even have a water temp gauge let alone an oil temp gauge,my 110 runs at 90 deg on the oil gauge and sometimes for no reason it will go to 100-110 deg,in my personal view it's a gauge i could happily do without,theres enough to worry about on the roads today without my oil gauge telling me the oil is a tad on the hot side,i think an oil pressure gauge would be more usefull

thanks for the replies, because it hasn't got into the red zone I suppose there is nothing to worry about because it does come down when the road flattens out, like grasmere59 says if the gauge wasn't there i'll be none the wiser, none of my previous cars have had an oil temp gauge and the thought of what my oil temp might have been has never came into mind, i'll just carrying on regardless and see it as a problem if it gets into the red.

So what is the best oil for the hdi 10w40 or 5w40?