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Discussion Starter · #1 ·
I've had my 01 LB7 for almost a week now, and even though the ambient temps are around 60-80F, the truck never gets past 180 degrees water temp. I've had it on the freeway, raced a few cars on the streets :? , but it still runs really cool. None of the 3 other diesels I've had have done this. Any idea what gives? I may invest in one of these mesh nets across the front to cut airflow, especially with a Minnesota winter approaching.
 

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Discussion Starter · #3 ·
Better than being stuck closed :lol:
 

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Discussion Starter · #4 ·
So how do I tell if it's the front or rear thermostat?
 

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2021 GMC Sierra 2500HD AT4
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I would guess the low temp thermostat stuck open which I believe is the forward thermostat. They're both right there next to each other though, if it were me I'd do them both. Your fan clutch isn't staying engaged is it?
 

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Discussion Starter · #6 ·
No the fan has come on once, and that was only because it had been sitting for a while. O'Reilly has them for like $30 so I'll do both. Any special tips? I've never done a t-stat before.
 

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Discussion Starter · #8 ·
Looks easy enough, but the Interwebs say a lot of LB7 owners have the same issue. It seems that replacing them is a crapshoot, and it's hard to tell if it will run warmer with them replaced. The previous owner cut a hole in one of the front wheel wells, and it also is missing the front skid plate, so it's getting way more air than originally designed.

I'll give it a shot, but I'm not expecting miracles.
 

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I would replace them both. And yes they do go in a certain way. There should be a drain plug in the passenger wheel well to drain the coolant. Only need to drain about 2 gallons. I would also look at doing the temp sensor too. It is right there as well. And make sure that you bleed the coolant after you fill it. There is a bleed screw on the thermostat housing.
 

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There's nothing wrong with extra air entering the engine. The classic body style duramaxs have an air issue with hot air being thrown into the intake by the fan and having the headlight block it pretty badly. The more air the better for the NBS body style. Definitely sounds like a Tstat. I'd get an OEM replacement Tstat because the aftermarkets suck, they don't operate as they should.
 

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Discussion Starter · #11 ·
Thanks for all the advice guys. I'll try to tackle it next week or so.
 

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Discussion Starter · #12 ·
New t-stats in today, as well as a new coolant sensor. Instant fix. The old ones seem to have eaten their own o-rings, so they were all kinds of messed up. It runs much warmer now, but still not even close to what a gas motor would run... or even the LLY or LBZ I used to have. Oh well.

I cracked the bleeder screw after warming it up, and only got a few bubbles before it ran pure coolant. Hopefully I didn't get too much air in the system.
 
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