Baja

I have a question about the thermostat bypass. As the title says, how important is it, any harm in using a thermostat without the bypass? From the manual all it seems to do is keep the water in the engine until it warms up, making it it quicker to warm up, that's it. Anything else I should know about? The reason is that I want to put in a 190 degree thermostat, but I cannot find one with the bypass on it, it is just a straight thermostat.

dozer12216

Find a Cummins shop and have them order if not stocked. Or a Dodge dlr can still get, I would think. No bypass no temp control.

wurkenman

I got mine at NAPA. about 30 bucks if I remember.

Baja

Did your thermostat have the bypass valve? I can also get one at Napa, but it will not have the bypass valve.

wurkenman

It looked just like the one I took out. Had the two little holes on each side of the flange, I'm guessing thats the bypass?

2500

so who's got 190 degree thermostat's?

wurkenman

I do I do I do

2500

great... now how do I get one?

called napa ... they've never heard of a 190 available

Baja

The bypass is a small disc on the bottom of the thermostat. It opens and closes independently of the main valve. It controls the water going through the block during warm up. If your thermostat does not have that disc, it does not have the bypass. NOW, that being said, how important is this bypass arrangement? From what I can gather, not too important. I have read about many others not having the bypass and everything works fine.
I installed a Carquest #30239 195 degree thermostat yesterday. The temp gauge will fluctuate between, my guess, 210 and 185, back and forth. Personally, right now I am not happy with that movement although I really need to do more driving to test it and maybe get more comfortable with it. I may stick in a 190 to see if there is any difference. Napa does make the 190, they were used in the older big block gassers of yesteryear. Be sure that the diameter is 2.5", apparently the 24 valve is a smaller diameter, not by much. As far as I know, they are not interchangeable with the 12v.
A bit of caution on draining the radiator. If you use the petcock in the lower left side be careful. It is easy to pull all the way out by accident and it is easy to strip putting it back in. Dealer cost for a new one is 8.00. Don't ask how I found out.

bmoeller

The swinging needle is normal. The coolant temp its self doesn't change that quick. Has to do with the sender location.

I replaced my stock 190* t-stat with a 180* stat from Cummins. Holds steady. Barely has to move when towing either.

Baja

I replaced my stock 190* t-stat with a 180* stat from Cummins. Holds steady. Barely has to move when towing either. [/QUOTE]

Some swing, some don't. My stock 180 was rock steady no matter how I drove the truck, no matter how hot outside. My new 195 is all over the map. Lots of posts have been written about the t-stat swing.

Where did you get a stock 190 for your 97 12valve? Cummins does not make one, at least according to my local Cummins dealer.

cLAYH

Someone explained to me once that the Cummins 180 t-stat is FULLY open at 180 and the aftermarket ones(NAPA) START to open at 180. Depending on how fast they open/close may explain the swing some people are seeing.

WestTN

Geno's has the thermostat in stock. And constant cycling is NOT good long term. This increases wear on the engine as well as the thermostat.

infidel

I think the cycling isn't as bad as all that and as said has more to do with the sender location. I had a highly accurate digital oil temp gauge for several years, oil temp barely fluctuated once it was warmed up even when the engine coolant gauge was going up and down. That's why I finally removed the gauge, it was boring but it did indicate to me that the block temp was very consistent.

Both my trucks are nearing 300k with the fluctuating original stock thermostats with absolutely no engine work. If the fluctuation is causing wear think I can live with it.