I just picked up a 1976 240D 50,000 miles, bought a new thermostat and it doesn't open till 190deg does anyone know what size is supposed to be in there. Also will 15w50 work in this car I live in ok.

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I do not know what the spec is for your t-stat. but I do know we do not need another oil thread! There is more information, emotion, heat, light, erroneous misinformation, etc, already posted on the topic of OIL than you can read in a day or two of browsing.
You might also find the answer to your T-stat question.

Oh, before I forget, welcome to the site!

Amen to the first answer...
80C is typical of Tstats.... what does 190F convert to on the C scale ? Hint-- 212 = 100

I would suggest you get yourself a Haynes Manual it would be a good thing for you to have and will answer alot of your questions, and as far as the oil if you choose to use a non synthetic Chevron 15w 40 would be fine and you can pick that up at any wal-mart. less tha $6 a gallon filters shouf be Hengst or Mann which you can get here from Fastlane. Remember change it hot and change it often every 3000 miles.
Hope this helps and again welcome

Welcome aboard. I second the recommendation to buy the 123 series manual from Haynes. For what weight oil to use, look at your owner's manual, or if you don't have one, again the Haynes manual will help. 15W-40 is the universal weight for any diesel and it is good for temps as low as 5. You mentioned 15W-50, which is only available from Mobil 1. I too won't get into a oil debate. I will just simply say, follow the owner's manual, and change the oil often. Oil is cheap, diesel engines are not.

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50,000? Remember it's a 5 digit odometer, could be 250,000...

Thanks for the info I found out that they had the wrong thermostat in the box put the right one in and works like it should.
This car has been in storage since 1991 so changed all the fluids have records back to the first owner so know the mileage is correct, just have to get it cleaned up and back in shape when they put it in storage they put it in the barn