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Discussion Starter · #1 ·
Hello, new here, but had a question. I have a 99 Sierra 2500. It has a 7.4l 454 engine. I notice that when I an in idle or parking the 5th wheel, my temp will stay at or just below 210. Once I give it gas or get going, the fan kicks on. Shouldn't I hear the fan in idle too. I'm thinking the clutch fan or relay switch not working. Our is this ok?
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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I'm confused. You have electric fans?
 

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2000 Silverado Z71 4x4 5.3L 460k+ miles w/ GM rebuilt motor and trans
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OK. Just making sure. The relay reference in your original post threw me. :unsure: Is this behavior a new development?
 

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Discussion Starter · #6 ·
Sorry, it's been doing it for a while, but usually when truck has a load. Now it's doing it in idle no matter what
 

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The fan should be spinning at idle but it does not necessarily mean you will hear it, pop the hood and check. As you initially take off you or give it a little gas will notice the fan get louder this is common on GM vehicles but as you get up in rpm or start driving down the road it should quiet down. What you don't want is a stuck fan clutch that can be a recipe for disaster.

Just below 210 is normal that is about 195 range which is where your OEM thermostat would open.
 

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Discussion Starter · #8 ·
The fan should be spinning at idle but it does not necessarily mean you will hear it, pop the hood and check. As you initially take off you or give it a little gas will notice the fan get louder this is common on GM vehicles but as you get up in rpm or start driving down the road it should quiet down. What you don't want is a stuck fan clutch that can be a recipe for disaster.

Just below 210 is normal that is about 195 range which is where your OEM thermostat would open.
 

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Ok, and if it creeps @ or just a little over, this is ok too?
I personally wouldn't be very worried unless it starts creeping up towards 220 range then I would pull over and let it cool down but that is probably just me, some people will probably be perfectly fine continuing on in that range. Verify your temp gauge is accurate though they can be a bit off on GM vehicles sometimes.

Do you tow often? I would consider running a bigger aftermarket transmission cooler something many seem to not think about.

by the way are you sure you have a 7.4? because it seems the biggest engine the 1999 came with was the 6.0, so was it swapped?

Also because they are so cheap just go ahead and replace your thermostat.
 

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Discussion Starter · #11 ·
I personally wouldn't be very worried unless it starts creeping up towards 220 range then I would pull over and let it cool down but that is probably just me, some people will probably be perfectly fine continuing on in that range. Verify your temp gauge is accurate though they can be a bit off on GM vehicles sometimes.

Do you tow often? I would consider running a bigger aftermarket transmission cooler something many seem to not think about.

by the way are you sure you have a 7.4? because it seems the biggest engine the 1999 came with was the 6.0, so was it swapped?

Also because they are so cheap just go ahead and replace your thermostat.
 

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210 is a little on the high side, but not much. As mentioned 195 is most likely the thermostat that you have, but if the temp starts creeping up at idle, then the fan is not doing its job as it should. IMO it sounds like the fan clutch may be starting to get weak. You may want to replace the fan clutch. Do you have an electric fan as an extra fan. Some do and some dont. Also the 7.4L have always had cooling issues. They are known for that. It takes a lot of air to cool that big engine. If there are any restrictions inside of the cooling system, this will effect cooling capacity. An electric fan swap can be a grate upgrade, but it needs to be a big enough setup to move a lot of air.
 

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the engine temp is at 195F .. if the temp changes then the radiator cap can not be holding pressure. also you have to remove the radiator cap start engine and run the engine to the normal temp rev engine some air in the coolant system . could be a heat issue .. .. some have this problem with air in the system.... then if it is fixed and a few days later it comes back then you have a coolant leak.. water pump ? or other components ..

fan clutch at idle does wear out for a couple of decades then the fan does not increase air flow at idle ..
wash radiator also clean it up fins look clean and fins are possible corroded .
T stats usually break down then the coolant temp will drop at a lower temp..
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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@Furious, the early ‘99’s came with the ‘98 GMT400 body and the 5.7 and 7.4’s until later in the year.
 
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