Thermostat size difference
 

Hi all, I posted earlier in the '7 heater hoses' thread and got all of the info I needed from y'all.

https://www.dieseltruckresource.com/...r-tank-323202/

I still have a question that doesn't involve the heater hoses so I thought I would start a new thread on it. The question I have is why there is a difference in the flange diameters between the 180* and 190* T-Stats I find listed for the `99 model 3500 SLT. The 180 is listed at 2.27" and the 190 is listed as a 2.39" for the same model truck. A tad over 1/8" difference. The old T-Stat, which the gasket is gone off of from removal, was a 180 and the one the parts house gave me is 190. I really would like to go back to a 180 since this 16 year old beast has been used to the lower temp all these years. Besides, I get queezy looking at that gauge sitting a little higher than I'm used to. Does anybody know if the 2.27 180 will work for this truck or if it will leak since it won't be as big?
Thanks for any help, Frank

I know my 01 takes a 190 and that is what I run, old posts talk about switching to a 180 for numerous reasons usually in regards to towing etc.

I went with a Cummins 190 when my stocker went out and haven't had any overheating problems even when towing at 97F ambient temps.

My advice would be go with the Cummins stat issued at build. Get the CPL number off your engine tag to get the correct one.

Thanks for the reply SIXSLUG. Now my next dumb question is where is the cpl tag on the engine and how do I read it to find the correct stat for my engine? I bought this truck at 6 months old from a friend of mine who pulled a heavy 5th wheel slide out camper and don't know if he changed it for that reason or if it's the OEM. You'd think I would know more about this old truck as long as I've had it. I can read the number on the old stat but can't make out the manufacturer. If I could find that out then I may be able to get the 2-25/64ths diameter like the 190 is.
Thanks again for your help, Frank

Be prepared for major sticker shock if you get it from Cummins. I wont say they aren't better than the cheap ones and I do use one (Cummins) but hold your jaw so it doesn't break when it hits the floor.
I have run both a 180 and a 190 in my 01. With the 190 I noticed significant swings when it opens up and then it just sort of cycled between open and close meaning it will open and the temp will drop then it will close and warm back up and open that doesn't seem to be the case with all trucks but I was not the only one that saw that happen and for whatever reason it doesn't seem to do as much now though 330k on my truck now. So many years ago I switched to the 180 just to get rid of that swing and it did. The 180 worked fine for me I never had any problems with it giving me heat in the winter time, warming up or anything else. However when it failed at some point I did go back to the 190 simply because that is what came on the truck originally. So as far as working either one should work as far as the size issue don't know but both worked fine in my truck with zero issues but they were both from Cummins not aftermarket.

I guess YMMV. Literally. I tried the 180 stat and found a *shocking* drop in fuel efficiency. I could go look it up, but off the top of my head it went from 18 to 15mpg. Immediately came back up when I put the 190 back in.

My cheapo 190 Napa stat gets rid of the "swing" too. But they also allow the engine temp to climb a little due to lower flow. Sits super steady at 190, but when loaded heavily, climbs to about 205-210 until the load drops back down. To me this reads as a function of limited flow.

At some point I'll put a Cummins 190 back in, it's sitting on the shelf.

Thanks for all the input y'all. I put the most mileage on it today, about 140 miles, since I reworked the whole system. Temp fluctuated between about 180 and 190 with the AC going and upper 70's to a high of 85 ambient temp. That's guesstimzation by the factory temp gauge. Each time we stopped somewhere I would check the reservoir and check for leaks. I'll know for sure in the morning once it's cooled completely down and drawn back on the reservoir. Maybe I'm just being too paranoid about it since it has my attention now. I never had to monitor the reservoir constantly before. The Stat I put in is a Stant and they have been around for a long time so I figure they are dependable. Now you guys have me wanting to look into the Cummins stat. I'll be sure to be sitting down for the price. ;-)
Thanks for all the help and I'll post back with the final results tomorrow.

The engine tag should be on the forward, top drivers side just behind the injection pump.

There is an outlined box with CPL and a 4 digit number. This number gets you the correct parts for a lot of items specific to your engine.

My Cummins stat was 62 bucks from a Cummins parts supplier...my jaw didn't drop very much.

Thanks for that location SIXSLUG, I'm going to look for it tomorrow weather permitting. Seems we're going to get a mess of rain from that hurricane here in Humble, TX. $62 for the Cummins doesn't seem all that bad considering I paid about $32 for the Stant. My jaw dropped at that though. Don't think I've ever paid more than a 'dollar two ninety nine' for the ones on my other vehicles. Just came in from checking the reservoir after the engine has cooled for about 7 hrs and the level is still about 1/4" from my pencil mark I put on it the other day when the engine was cold and the ambient was in the mid to high 60's. Then maybe it was in the low 70's. That was before I got up this morning so it could have been in the teens and I wouldn't remember. :-( That 140 mile round trip to the country to the house we are trying to buy has sure eased my mind and nerves. Don't need anymore major truck expenses right at this time.

Dont run the 180* in the 24 valve because its too cold. The 24 valve head flows so much air that it needs the warmer thermostat in order to run most efficient and produce normal power. Plus running a cooler thermostat in cold climates will create cylinder wash as proper combustion isnt taking place due to the lower cylinder temps. All these will generally result in lower fuel mileage, slight loss in hp, and you'll need to change the oil more often.

Run the 190* and you can get it from NAPA or Cummins. The Cummins is obviously more expensive so NAPA is a good alternate as long as you make sure you're getting the right Cummins model thermostat. Meaning it must have the outer rubber seal and the two jiggle pins on the housing plate. If not then its not the right one.

There's even been people who tried the 200* thermostat to help with mileage and power. It works but unfortunately if you live where the ambient weather is not sub zero and/or you tow heavy then the 200* can easily prove too hot and resulting in excessive engine temperatures.

And I'm not sure you were seeing different size thermostats. Most likely they were not for the same engine even though the computer said so. There's a lot of incorrect cross information out there because both the 12 valve and the 24 valve were available in '98. :thumbsup:

Thanks KATOOM, Your advice makes sense. I went out this morning while the ambient was at about 75. and the coolant level was still about 1/8" to 1/4" above the last pencil mark I put on it so I'm not losing coolant. When I reworked the system we were having ambient temp swings from high 50's to around low 90's. Since I've never watched it this close before reworking, I didn't really know how to reference my levels so I was concerned. I have decided to leave the 190 in as you guys have suggested. I did notice my mileage improved when we went on the 140 mile trip yesterday, 22.+ mpg with the wind and 21.+ into the wind coming back. It had been gradually decreasing over time and that must have been because of the 180* plus the old stat's rubber valve seal had developed several cracks in it and was allowing coolant to bypass even thought the valve was closed. No wonder it took so long to come up to temp. Do any of you have a link to a good genuine Cummins supplier? All I've come up with is the Cummins Quick Serve and and I think it's for dealers and service shops. Thanks again for all of y'alls help.
I'd be SOL (Seriously Outta Luck) ;-) without the help from you guys here. :cheers:

Try looking for Cummins location near you. Out here its call Cummins West but I have no idea what they're called in TX. If you want OEM then what you're looking for is Cummins part number 3954830. Google it and maybe you'll find places on like that have it. :thumbsup:

There's bound to be one here in the Houston area so I will do just that. First I'm going to wait for the remnants of Patricia to pass through then go out and find my CPL tag on the engine that SIXSLUG mentioned. Lord the things I don't know about my beast! But then I've only had it 16 years so how could anyone expect me to know much about in that short period of time? Then again, I do know more about it than I do the better half and I've had her longer. LOL

Thats why most people refer to their vehicles as "she". Dont bother to know anything about her but always fun to mess around with. [laugh]

Hmmm, you're so right. [laugh]

Like Katoom said, I chose to stay with the stock 190. I've been in temps around 100F and don't have any hot issues, hangs around 190 and I can see the gauge drop a bit when it opens during cooler temps and my mileage is good.

The extra bucks are worth knowing I shouldn't need to worry over it for quite a while. I assume the stock one went to around 120K miles, I bought the truck bone stock with 43K on it....