T-Stat for SD220


IHC in the early to mid-fifties.

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Post Mon May 27, 2019 6:00 pm

T-Stat for SD220

I need a new thermostat for my SD220. First question, what is the recommended temperature rating? I looked in my shop manual but I couldn't find any info. Second question, sources? NAPA lists one but no mention of temperature rating I'll check with them tomorrow, anybody else sell them (besides Rockauto)?
56 S120 4x4,

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Post Mon May 27, 2019 6:02 pm

Re: T-Stat for SD220

180-192 deg F
No engine using ethylene glycol antifreeze should ever need a 'stat that is cooler than above.

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Post Mon May 27, 2019 6:19 pm

Re: T-Stat for SD220

Thanks, I had 160 in mind so that is good information to know!
56 S120 4x4,

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Post Mon May 27, 2019 6:39 pm

Re: T-Stat for SD220

160 was used back when antifreeze was made with Alcohol as the main ingredient. Even at 160 the alcohol would "cook out" of the coolant, and had to be replenished.
Ethelene Glycol fixed all that and was called permanent antifreeze.
160 was less than ideal temp, but it was as hot as practical with alcohol. 180 or 192 is far better and the new antifreeze will not boil till close to 224 deg with no pressure cap, so plenty of room left even at 192.
Remember the thermostat only sets the MINIMUM temp of a running engine, it has nothing to do with how hot it will get above its opening temp.

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Post Mon May 27, 2019 7:32 pm

Re: T-Stat for SD220

Remember the thermostat only sets the MINIMUM temp of a running engine, it has nothing to do with how hot it will get above its opening temp.[/quote]


I think I'll be OK in that dept. I had it idling today in 70 degree weather with the old 'stat and it wouldn't go over 120 degrees and after 15 minutes of that I could still touch the base of the carb without burning my finger so I don't think over heating is going to be a problem with this engine and radiator.

Also thanks for explaining why the old anti freeze system ran the temperature it did as opposed to the new, I enjoy learning this stuff.
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Post Tue May 28, 2019 7:57 am

Re: T-Stat for SD220

These should be good numbers for the 180 degree thermostat, but I haven't checked them for a while. Gates #33198, NAPA #THM142, Superstat #THM533080, Stant #13368/35368. NAPA Premium 180 Deg. –THM533080

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Post Tue May 28, 2019 9:37 am

Re: T-Stat for SD220

Not owning anything in the "light line" I might be off base, but I do remember one engine or T stat housing requiring a "spacer ring" to hold the T stat in position, without it, the stat will be useless. I thought it might be the SD series?
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Post Tue May 28, 2019 12:09 pm

Re: T-Stat for SD220

It is the SD series. The thermostat goes up in the neck, with the spacer ring under it.

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Post Mon Aug 12, 2019 2:30 pm

Re: T-Stat for SD220

I have always been a fan of running cooler thermostats and have even run a couple without a thermostat, but I also live in an area where temps can exceed 110F in the summer. I find that every little thing I can do to help the cooling system is helpful.
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Post Mon Aug 12, 2019 10:35 pm

Re: T-Stat for SD220

A 'stat can provide a very necessary restriction in the flow. Without it, coolant can pass thru the radiator faster than it can transfer heat to the air. It also can raise the pressure in the block higher than the radiator cap pressure, eliminating hot spots, and cavitation damage caused by coolant boiling at the head or cyl walls. It is why Speedway and Summit sell restrictor plates for the 'stat housing when no 'stat is used. A Cummins Big Cam 4 will run 45 psi block pressure (at full governed speed) with a radiator cap pressure of 4 psi.
Low temp 'stats will NOT prevent overheating. the "stat only sets the minimum temp.
Vehicles with an oversize radiator that isn't well maintained can sometimes benefit from the increased flow when the stat is removed to "clear the tubes" but once they are clear and the system is flushed, then a 'stat should be installed.
A radiator only needs to drop the temp 10-15 degs F to keep the engine from overheating. If it can't do that, then either the system is clogged or the radiator is too small.
With a lower temp stat, all the coolant can be held at 160 where as a higher temp 'stat will keep the flow down and the coolant in the radiator will be cooler than it would be with the lower temp 'stat.
Either way, if the system can't handle the engine heat at full throttle, it isn't a question of "if it will overheat". but when.
The hotter the engine can run, the more efficient it will be.
My Truck has pulled steep grades where I have been running flat-out at 25 mph for 45min without a break, that is a test that most vehicles will never see.
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