Changing Coolant - Thermostat too?

[MSkyrman]

It is time to change the coolant again (just the second time). Mileage is at roughly 170,000 and the thermostat is original. No cooling issues and wondering if the adage "if it ain't broke, don't fix it" applies here. Or if I should just replace it while I'm changing the coolant since it's inexpensive to do so.

I see Geno's has a 180 degree and a 190 degree thermostat. What factors go into deciding which one to get? Seems the OEM one has always done well, but not sure it is 180 or 190. Thanks.

 

[AH64ID]

I am at 106K and on my 3rd thermostat, first was needed at 55K and second was done with coolant/etc 94K.

The thermostats in these engine get accelerated wear if you don't tow heavy and often becuas they rarely go full open. When I was towing at 14-15K GCW the thermostat would only go full open 7-10 times a year, now at 19-20K GCW it goes open on most 6% plus grades, and should last longer.

So I would change it. OEM is 190° and if you do any towing the 190° is needed for proper fan operation. Stick with OEM Cummins, plenty of horror stories on the non-Cummins thermostats.

The biggest indication of a sticking thermostat is how it gets before it opens on the initial opening of the day. The 190° should be open by 194-197, usually 194-195 unless your towing. When they start to go they can sometime get as high as 207° before opening.

The extreme size of the cooling system masks most thermostat issues on the 5.9. The 6.7 has a smaller system (almost 2 gallons), with more OEM power, so issues are more pronounced.

Having an OBDII reader makes it much easier to see the issues than the OEM gauge.

 

[TRAMPLINEMAN]

My '06 was a 190 stock. I bought a spare in case the stocker ever quit. I too NOW believe if it's not broke don't fix it. I never changed my '06 and it was still working with over 200K on it. I changed my '97 years ago when I changed the coolant cause it was handy. Not so much. The new one quit within a couple months and so did the next one after that.

 

[Prairie Dog]

Don't forget about the radiator cap too. They get weak over time and you don't know it until it's too late.

 

[BDaugherty]

$260k on my OEM Tstat. Leave it be until it causes trouble.

 

[Prairie Dog]

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Great advice, save that $12 for a head gasket.

 

[CToney]

My 05 would run warmer than my 03 so I decided to change the thermostat. The rubber seal on the old one was in tough shape. The new one has a different part number but looks very similar. My 05 warms up way faster than my 03 too. I'm going to change the thermostat in my 03 to see if it helps it warm up faster. It's super easy to change. I'll maybe have to get a couple of rad caps next time I'm to town. I'm sure they're original on both of my trucks.

 

[MSkyrman]

Thanks all for your sage advice. I appreciate your insights.