Help! My coolant temp heats up fast in idle or slow-moving traffic (around 210F+) then decreases when I start driving (around 170F-190)

[Cj1234]

I have no idea what is wrong. PLS SEND HELP

 

[Captcorvette]

I have no idea what is wrong. PLS SEND HELP

Sounds like a bad clutch fan not working at low rpm.

 

[Jgonick]

Sounds like a bad clutch fan not working at low rpm.

Just about to say the same thing. Check to see if your fan is working correctly.

 

[Radiohead]

Either low fan throughput, lack of proper shroud or a bit of coolant flow restriction.

 

[Vbb199]

Water pump or fan clutch

Does the fan turn freely when the engine is cold? Or does it have a bit of resistance.

 

[Broken85]

If the fan keeps spinning after you shut off the truck, then (as stated above) bad clutch.

 

[75gmck25]

Check the fan and shroud with the engine off. Is the shroud in place? What type of fan?

If it’s a stock mechanical fan (no clutch), the belt should be tight and the fan should not move when you push on it. It is always coupled to engine speed.
If it has a flex fan, throw it away and find a stock metal fan.
If it has a fan clutch behind the metal fan, the fan should move when you push it (engine off), but have moderate resistance. Then start up the truck, let it run a few minutes, and shut it down. Now the cold fan clutch should have distributed the fluid and the fan should move freely when you push on it (engine off).

Start up the truck with the radiator cap off, and look down into the radiator where the heater hose connects. If you see water gushing into the radiator, the water pump is moving water and working.

 

[Fitz]

Most likely a worn out fan clutch. I use the Hayden 2797 Severe Duty fan clutch on all of my trucks. The severe duty locks up sooner. And free wheels later than the standard duty, or heavy duty ones. Yes, it will make more noise. I would rather have a fan making more noise, pulling more air. Than one free wheeling and not pulling air through the radiator when it needs to be doing just that. Along with the 7 blade G.M. fan blade, or aftermarket one. Make sure to also use a fan shroud to "funnel' the incoming air across the radiator. Hope that helps. Semper Fi. OUT!!!!!

 

[59840Surfer]

Most likely a worn out fan clutch. I use the Hayden 2797 Severe Duty fan clutch on all of my trucks. The severe duty locks up sooner. And free wheels later than the standard duty, or heavy duty ones. Yes, it will make more noise. I would rather have a fan making more noise, pulling more air. Than one free wheeling and not pulling air through the radiator when it needs to be doing just that. Along with the 7 blade G.M. fan blade, or aftermarket one. Make sure to also use a fan shroud to "funnel' the incoming air across the radiator. Hope that helps. Semper Fi. OUT!!!!!

I tried the Hayden HD and my gas mileage got a big 3MPG hit beside the intense roaring.

I ultimately went to the dual electric fans and wired them up like my '05 GM trucks --- low voltage and high voltage (6V v 12V) and got my mileage back PLUS!

FTR ---> Newer GMs with dual fans, use a Series/Parallel relay system that gives 2-speeds to the fans.

If you're tricky and know how to use a pair of diodes, you can get 3-speeds!

Back to topic --- the Hayden is a lot of overkill IMO.

 

[cadillac_al]

It's always nice to have a new fan clutch. If that doesn't fix it then I think it is a radiator flow problem. I have a bad fan clutch and my truck only overheats in high gear. It doesn't overheat at slow speeds. When it starts getting hot I put it in 2nd gear and drive slower and I can watch the gauge go down. High gear really puts a load on the engine.

 

[Matt69olds]

First, 210 at idle isn’t terrible. If that’s as hot as it gets, I’d say you’re trying to fix a problem that really isn’t there. Make sure the fan clutch works as it should, and the shroud fits well.

You can easily test the fan clutch, throw a heavy blanket over the front of the grill (make sure it won’t get wrapped up in the fan!!) start the engine, and rev and hold at around 2500 rpm. If everything is working as it should, as the engine warms up you should notice a distinct roar from the fan, with a noticeable increase in airflow. Once you hear that, remove the blanket. As the engine cools, the roar and airflow should decrease.

Just don’t overheat the engine!!

 

[Cj1234]

I have dual electric fans and an aluminum radiator what should I be looking for?

First, 210 at idle isn’t terrible. If that’s as hot as it gets, I’d say you’re trying to fix a problem that really isn’t there. Make sure the fan clutch works as it should, and the shroud fits well.

You can easily test the fan clutch, throw a heavy blanket over the front of the grill (make sure it won’t get wrapped up in the fan!!) start the engine, and rev and hold at around 2500 rpm. If everything is working as it should, as the engine warms up you should notice a distinct roar from the fan, with a noticeable increase in airflow. Once you hear that, remove the blanket. As the engine cools, the roar and airflow should decrease.

Just don’t overheat the engine!!

should not move when you push on it. It is always coupled to engine speed.
If it has a flex fan, throw it away and find a stock metal fan.
If it has a fan clutch behind the metal fan, the fan should move when you push it (engine off), but have moderate resistance. Then start up the truck, let it run a few minutes, and shut it down. Now the cold fan clutch should have distributed the fluid and the fan should move freely when you push on it (engine off).

Start up the truck with the radiator cap off, and look down into the radiator where the heater hose connects. If you see water gushing into the radiator, the water pump is moving water and working.

 

[Cj1234]

I tried the Hayden HD and my gas mileage got a big 3MPG hit beside the intense roaring.

I ultimately went to the dual electric fans and wired them up like my '05 GM trucks --- low voltage and high voltage (6V v 12V) and got my mileage back PLUS!

FTR ---> Newer GMs with dual fans, use a Series/Parallel relay system that gives 2-speeds to the fans.

If you're tricky and know how to use a pair of diodes, you can get 3-speeds!

Back to topic --- the Hayden is a lot of overkill IMO.

I have dual electric fans and an aluminum radiator what should I take a look at?

 

[59840Surfer]

I have dual electric fans and an aluminum radiator what should I take a look at?

First --- what is your intention?

Do you want then to run just one speed or would you like them to run as two speed fans?

 

[59840Surfer]

To keep this simple --- even though it looks complicated --- it can be done to any dual fan system with the addition of one more coolant temperature sensor and some relays and a bunch of wire --- but I'll post a drawing of the way it should go for a two speed dual fan system ...

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1. #s 1 & 2 are the dual fans.
2. The "180" references the temperature sensor that closes at 180°F
3. The "200" in green references the additional 200°F sensor --- more on this later.
4. "Step 2 High" is the 2nd half of the wiring that gives the HIGH-speed Voltage to the fans.
5. I assume one can recognize the BATT and what's not listed directly from the BATT on the + side is a fuse --- two of them - one on the LOW SPEED and the other on the HIGH SPEED.
6. There are TWO 4-pin relays
7. There is ONE 5-pin relay.

♦ If anyone wants to do this --- I recommend wiring up the LOW SPEED first! Do it through the relays where necessary, using them as junctions at this point until the second speed is wired-in.
♦ It really is easy! Believe me! .
♦ You'll find these relays do not countermand each other but they are called in at their particular time.

PS ---> I will provide a schematic of a 2005 GMC truck with this same circuit in it --- it will be the same wiring except for the temperature sensors --- the fans do not directly run from their commands, instead modern fans they get their commands from the ECM.
♦ We don't need no stinking ECM for two-speed fans!

Following is the 2005 GMC version that we are emulating.

It complies with the same inputs, but since we don't have an ECM on most older GMs, we are having to use two temperature sensors instead.

As to all the stuff in the lower left corner; we will have the two sensors performing this function where you see: PCM.

In essence, the ECM has two relay controls that we will replace with the two coolant sensors we install --- it's that simple.

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