So I did the thermostat mod (drilled 5 holes in it) and went for a test drive. I'm pleasantly surprised that it did a lot to bring the engine temps down. I got to about 85 Celsius and that's it. That's about 15 degrees cooler! I did the test drive with the A/C running full blast just to add a little more heat to the system and really test it. I haven't tried this mod earlier because I tried running without a t-stat installed and still had overheating issues. I then found out that no t-stat will actually cause overheating on these cars. Wow, I never would have guessed that... especially since my engine would not warm up beyond 40 when my last t-stat failed. I guess the cooling system has to have at least some restriction to work properly(that sounds weird to say).

So it is pretty mild temperatures here in Dallas right now. But I'll stay hopeful that the hot summer time won't cause this problem to resurface once again.

I think I will still end up doing the block test kit though. I really don't like not knowing what is making me have to drill holes in my t-stat. And if my head gasket is leaking just the slightest little bit, I want to know!

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Cousin Dave
83' 300SD 250k+ and going strong!

Take the best that exists, make it better!
If it doesn't exist, create it!
Accept nothing nearly right or good enough!

he stated he "traded out his fan clutch" does this mean a NEW clutch was installed, or just another used one from a different car?

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Get the one from Napa. It works on diesels and is roughly the same price. It is described more completely here:
Block Tester Combustion Leak Test for Blown Head Gasket by Test Tools inc.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).