Thermostat Replacement 200TDi

[DBrands]

Serves me right for taking this on while it was -15C, but I'll pass on what I learned.

I've been driving the 90 daily and noticed engine temperature falling in cold temps at idle.
The upper radiator hose was also warm even before the engine reached operating temps. Time for a new thermostat!

I pulled the thermostat out (Waxstat). Tested it against a new Waxstat and no-name thermostat; there wasn't much variation. The used Waxstat closed slightly slower than the new, and the  no-name was even slower...so I changed it up.

I replaced the used Waxstat with the new Waxstat, a new paper gasket and a bit of gasket maker. Nipped up two bolts, third never made it.
Drilled and tapped for M8 instead of the original M6. Re-filled with coolant and it leaked immediately from under the outlet.

I pulled everything off, cleaned up the surfaces and tried again. Pulled out the threads on the second bolt... tapped for M8.
Now, still leaking, but less. Pulled everything apart and laid a straight edge across the lower housing. Things weren't flat... Time for a new strategy...

Here is where I noticed a lot of play between the upper and lower housing, even without a gasket. I assumed that it would be a reasonably tight fit, with the recesses in each half of the housing locating the thermostat precisely and keeping things tight and sealed (no coolant flow around the thermostat). Now I started to wonder whether my original thermostat was indeed fine, and the fact I had a paper gasket in as well as a dab of gasket maker, had coolant flowing around the edges of the thermostat. Hmm...

In the meantime I'd remembered reading that people were having success with Ford V8 thermostats, so I went and picked up a MotoRad 'Ultrastat' Part# 5228-195JV as I couldn't locate a Stant 'Superstat' Part# 45779.
It appears they are both a similar design with a profiled rubber seal to help moderate coolant flow.
The flange on the MotoRad was similar in thickness to the Waxstat (the sealing ridge on the circumference was not quite as proud). Dry fit things again with the new thermostat and similar concerns that the top half of the housing didn't 'locate' itself on the thermostat as well as I would assume it should to keep a tight seal.

I decided to sand down both mating surfaces slowly to get them flat (I assume this contributed to my leaks earlier), and until I noticed that the upper housing was 'locating' on the thermostat.

Once I got the mating of the surfaces and thermostat to where I wanted them, I skipped the gasket and just used some Permatex 'Ultra' RTV. No leaks!

Now at -15C, the truck warms up in ~5-7 minutes of driving without issue and maintains operating temps even at idle below -15C. Success!

[bumpydormobile]

Thanks for sharing that David

[Matt H]

Cool....er I mean hot!