WWDiesel wrote:
Everything rancherman stated is relevant and should be considered. But that in-line thermostat is believed by quite a few to have caused several blown head gaskets and possibly a couple of cracked heads as well. Some will defend its use, but unfortunately there is no definitive way to prove that its use is detrimental other than looking at the design of the engines coolant system itself and what can happen when you run this engine with a failed OEM thermostat with the bypass circuit closed off and a closed in-line thermostat which will limit proper coolant flow through the head during the critical warmup period and may cause some serious "hot spots".
Best options are to use either a good fully functioning OEM thermostat (no Crown Junk) or one of Jeff's a.k. "Turbo-Diesel-Freak" H.D.S. Model 001 thermostats.
There is plenty of reading on this forum on this subject as it has been debated and discussed in detail if you want to do a search.
Bottom line, In-line thermostats are simply not worth the risks and possible consequences when used on this engine's coolant system.
The misery of an inline, we don't know how 'bad' the stat is that is STILL installed.. Is it getting worse? (more and more open) which means less and less bypass for internal circulation. I'm assuming the stat closes the bypass off at the same rate it opens for passing coolant to the radiator.
It's difficult to put detrimental damage on a 'per mile' basis.. So one guys 'no problem' for say, the past 1 or 2 years, with an inline could be the next guys 'worst nightmare' ie; One person that has an inline stat and this engine is 'cold started' several times a day, and put less than 10 miles on it. Might rack up 8, 9k miles per year..
Next guy would start his up in the morning, rack up 100's of miles before shutting it off... and puts 30k on his Jeep per year.
Which one will see 'issues' (cracks, scuffed gaskets..etc) first? I truly believe the first guy would. It went through 3x the cold start cycles. Per year, per mile.. I think it's the number of cycles that counts.
We have a cross flow head. cooler intake air is coming in one side, hot exhaust going out the other. One SIDE is going to expand faster than the other.. add this to the head-as-a-whole expanding faster than the block it's bolted to.
An engine with exhaust and intake on the same side tends to have a little tempering effect.. 'some'. We don't want that anyway!!... ports tend to be a lot smaller, and castings are thinner.. on those same- side designs. Think your engine is crowded NOW?? imagine it with the turbo and intake on the same side!!!
Add all these up, I'm seeing a great need to maintain a nice circulation within the head to keep this unevenness of temps moderated.
Also reinforces my statement of "proper heat up and cool down" And well maintained thermostat.
Can you imagine the thermal shock... on a zero degree day, and an engine with 900 degree combustion temps on one side of the cylinder wall is constantly getting 'washed' on the other side with almost zero degree coolant because the thermostat is stuck open??? brrrrr...