My OEM sat at 188*f for several years before it started really failing. I wouldn't replace a 190*f stat until it's consistently in the 170s-182, because they just don't seem to really be set at 190. More like 186-188 out of the box, but they'll hold that for a decent amount of time.

I was in CO this summer in July with the 200*f Mishi stat installed. Not towing, but the truck was at 10k, +1500# from "empty" for me.

Any kind of uphill at speed I was pushing 206-210*f pretty much constantly and the fan would start locking in. Going over Loveland Pass I hit 218*f and the fan was 100% locked in. Mind you I'm going speed limit +5-10 depending on where I was, and I wouldn't do that with a trailer. But a climb everyone pretty much knows, I-70 from Dillon to the tunnels, the fan was fully locked in around 212* to go 75mph in a truck that really isn't that heavy compared to one pulling a trailer. I'm not sure what kind of head room that would leave you if you're doubling the weight going up the hills, probably not enough.

My opinion is the temp at which is opens matters moreso because that's when it starts to close on the other side when it's cooling down. On the really hard pulls in the mountains opening earlier is a good thing because of the constant cycles the hills cause; the stat stays open longer on the downhill and lets the fan/radiator work faster to recover.

I'm not a huge fan of the 200* stat in hot weather in general, if I was towing anything down here I'd pull it out. After seeing what it did unloaded in CO, I'd probably pull it out if I was going back up there. To me the benefit is in the winter when the OEM stats just won't hold operating temps.

You might want to look into the Mishi 185* stat for the summer, I do like the quality of the Mishi, I just don't want to push 210* ECT all summer unloaded.

 

I could be wrong, but I'm thinking you have a cooling system issue. Maybe an egr cooler issue, a small leak that won't allow system to hold pressure, or a slight head gasket leak. I've never had my coolant temp rise that much, even when towing heavy (15k trailer with 6.0 truck, 20k trailer with 6.4 truck) through mountains of PA and NY in the summer. If your temp is rising that much with basically the equivalent of a few large adults and luggage in it I suspect an issue.

 

You do make a good point actually. Considering atmospheric pressure is a solid 4psia lighter at 12,000 feet compared to sea level, I don't think there's anything wrong with the truck as far a pressure leak, it's just the fact of the circumstances that there's a larger pressure differential and even a brand new degas cap holding back a full 16psig is holding back less pressure than at sea level.

Mark is pulling in Colorado, so altitude is a larger factor than elsewhere and I was trying to give him a narrowly tailored answer since elevation is NOT an issue in the majority of the US. The highest elevation point in PA is a solid 10k feet lower than the two climbs in CO I mentioned. My truck has been as high as 14,100' (MT Evans CO), which is almost an entire 1psia more of pressure loss over 10,000' starting that climb up I-70.

Also if you're towing you're likely downshifted, while I was in 6th going 75mph. You'll be pulling more air across with the fan because your actual engine RPM is higher than mine, and the fan speed is actually slightly ahead of engine RPM because of the size of the water pump and crank damper on the belt drive.

 

Good points on running up these grades empty even, I do run warmer even when not towing. Can't remember numbers though to compare, but I haven't seen 210+ not towing since I did my oil cooler even up these hills. Haven't been up through Eisenhower empty since my new oil cooler though.

That stretch from Dillon up to the tunnel is a bear! I pulled the camper this fall up that. This is after doing the oil cooler too with excellent diff's in EOT/ECT(less than 5 all the time even when towing). I got up to 237 EOT with 232 ECT before hitting the tunnel and the fan pegged. Once in the tunnel, both temps dropped into the low teens before exiting the tunnel. Now, I was pushing waaay harder than I would normally or should have. I pretty much maintained 55-60 all the way up, had to pass that Cummins and few a rice burners you know

These are the reasons why I was asking. These passes are hard work especially when towing. Starting 10*ish warmer before even starting up the passes seems counter productive. But I don't know for sure. I'm leaning away from the 200* Mishi to be honest. I hadn't noticed the 185* one before so I'll take a look at that. But, isn't that counter productive the other way when not towing since these trucks like it warmer?

I like working on the truck, but I don't want to be causing myself extra work switching the thermostat around for different applications all the time. Too bad Mishi doesn't have a 192* one to replace the standard version.

 

I'm about to do a flush and switch to Rotella ELC, glad I found this thread before I ordered an oem stat.

I've seen it mentioned you have used the updated Ford housing for it to work.
2 questions, My truck is an 05, do I have the updated housing?
Has anyone used the Mishimoto housing and stat? Part# MMTS-F2D-03FH
Mishimoto MMTS-F2D-03FH High-Temperature Thermostat & Housing

You can get it for 93 bucks. If you went oem it would be 56 for the mishi stat, 24 for the housing, 5 for the gasket. Thats 85 bucks right there.

 

You can use the updated Ford housing (no guarantee you have updated housing on an 05), a Mishimoto housing, or a Sinister Diesel housing (what I used).

 

one thing I ran into is what the Misi stat would not fit into the updated housing at first. Some told me to boil it because the wax and spring can do strange things while in shipping/storage. It seems like the rod is too long, but in reality it just needs to be reset by boiling it.

 

My 2007 didn't have the updated housing, so I don't think yours would.

 

Gottcha, thanks for the help. I'm actually kind of second guessing using that stat now. Summer is just around the corner here in SC and we get consistent 90-95* days. With my factory stat in 80*ish days my temps were around 194*ish, not really looking to up the temp in the hotter months to come

Plus after doing some more reading in here it seems like several have returned to using a new oem 192* stat after trying out the mishi. I need to read some more....

 

We're hitting the 80s consistently here already, if my ECT's cause the fan to lock in unloaded again this summer I'm putting the new Motorcraft stat that came with the updated housing back in. My old stat was staying down at 186-188*f so I put the Mishi in two winters ago. Wasn't thrilled with running 206-210 constantly and having the fan lock in so much last summer so I swapped the fan clutch to a non-plow clutch but didn't seem to help. If it's doing that again and hasn't settled down the 199-202 this year, it's coming out.

If I have to swtich them out I say NBD, it's a 15 minute deal if you have a Fumoto block drain. During winter was definitely worth it, running 202*f when it's in the 20s was great.

 

I was about to pull the trigger on a 200* but I'm in the same boat as some.I'm really not sure if I should switch from the Ford 192* or not.I did a flush a few months ago and my Ford 192 was running me 190-196 ECT so my delts were around 7*.With the new 192 I put in after the flush it's only getting me around 186*-188* so now my delta's look so much bigger when before they looked good.I like hearing guy's trucks are running good hotter but I don't feel that comfortable running 205*-210* all the time.

Grrrr

 

Diesels like running at those temps and better for them!

 

I know,Your right!Im just so indecisive!!!!

 

I recommend the Mishimoto 200 stat without reservation. I am totally happy with it. Previously I had put in a new Ford 192 stat and within a couple months I was down at 183 degrees, occasionally I could get it to 185. If it was below 50 outside oil temp wouldn't go higher than 187. Now I'm at 200 ECT and 203-205 EOT. Much happier motor...and noticeably better fuel economy.

 

Thanks