Engine takes forever to warm up

jlglr4 said:

Could this be a bad coolant temp sensor rather than the thermostat?

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oh man...i have to do some digging on this now.

Sorry - don’t mean to complicate things. There should be two coolant temp sensors. One just ahead of the thermostat (radiator side of the t-stat, actually included as part of the lower radiator hose), which measures the temp of the coolant coming out of the radiator before it goes into the block, and another at the back of the engine - maybe in the rear crossover if I remember correctly - that measures the coolant temp coming out of the block. I believe this latter temp sensor is the one the dash gauge reads.

Replaced the fan clutch. It was definitely stuck on all the time. Now the engine warms up to temp within 5 mins at idle vs 30 mins from before.

jlach993 said:

Replaced the fan clutch. It was definitely stuck on all the time. Now the engine warms up to temp within 5 mins at idle vs 30 mins from before.

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Awesome! 5 minutes is more like it.

jlach993 said:

Replaced the fan clutch. It was definitely stuck on all the time. Now the engine warms up to temp within 5 mins at idle vs 30 mins from before.

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That is bizarre. Temperature should be controlled by the thermostat, so even if the fan is on all the time, it should reach operating temp rapidly.

gsxr said:

That is bizarre. Temperature should be controlled by the thermostat, so even if the fan is on all the time, it should reach operating temp rapidly.

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I figure it won't do this if the sub-circuit that opens the thermostat is being cooled constantly by a stuck fan clutch and doesn't get warm enough to open the tstat until much later.

Well it definitely fixed my issue. Since changing the fan the vehicle warms up way faster than it did before. It's a night and day difference. I'm getting full heat within 5 mins of starting the truck. I don't even have to drive it.

That’s interesting. gsxr’s point seems valid. The thermostat isolates the coolant circuit from the radiator until the coolant hits 192F. At that point, the t-stat starts to open and allows coolant from the engine to start flowing through the radiator. Changing the fan should only make a difference if the t-stat is stuck open.

The one caveat is that the oil cooler might be taking coolant from the radiator bypassing the t-stat. Not sure. I guess that could affect engine temp some.

Could be the t-stat was stuck as well and you knocked it while changing the fan getting it to dislodge and close again. Or it might still be stuck open and your not actually getting all the way to operating temp as quickly as you should. If you have a Gap tool, you might check your temp on startup to see how long it takes to get to 192 or so.