Overheating at low RPM - thoughts?

Symptoms:

- Truck overheats at low RPM (stopped in traffic). Will do it at any outside temperature (20F-90F).

- Temperatures immediately drop to normal upon elevating engine RPMs - even in neutral.

- Thermostat has been recently replaced as part of diagnosing this issue.



I'm thinking fan clutch? Any thoughts before I replace that?

Update:

So I did some more investigation into the issue today. Sat in a parking lot with the truck idling for about 7 mins before it began to overheat. Fan was spinning the entire time. As soon as I drove away, engine temps dropped to normal within 30 seconds.

Thoughts?

 

I would look at airflow through the radiator and coolant flow through the radiator.

 

Either lack of air flow (ie fan problem) or possible issue with water pump/ coolant flow.

 

Have you done a hydrocarbon or combustion leak test?

 

Before you replaced the thermostat was the cooling system low on Coolant?
Had the Cooling System ever been opened, and Coolant replaced?
There could be air in the system. The Tacoma is known to trap air most of the time.
Air in the cooling system can cause the symptoms you describe.

I’d also look into the fan clutch. As this too can cause the same symptoms.
And I’m honestly leaning towards this, since you say it is ok at higher speeds.
At higher speeds the wind “cools” the radiator.

Also check the condition of radiator for damage.
If you have a digital infrared thermometer you can check the radiator for hot spots.
A thermal camera works a lot better, but most guys don’t have access to one. And they are a
expensive.

 

Fan clutch for sure. Check resistance of fan when the engine is starting to get hot, over 200. Should be good resistance

 

I'm willing to bet the fan doesn't spin, my Grand Marquis had the same issue. But does it overheat simply idling? If it doesn't then that deepens the mystery.

 

So I did some more investigation into the issue today. Sat in a parking lot with the truck idling for about 7 mins before it began to overheat. Fan was spinning the entire time. As soon as I drove away, engine temps dropped to normal within 30 seconds.

Thoughts?

 

Still sounds like a fan issue, it can be spinning but still not working well enough to keep the engine cool. I had this issue when I had e-fans installed...they just didn't push enough air at idle or slow temps. Once you get up to speed, the outside air coming through the grill is bringing your temp back down to normal.

 

Turn off the truck after it has gotten up to temperature and attempt to spin the fan. If there is resistance that is good. Move on to the next item.

Radiator could potentially be partially clogged, impeding airflow until it sees some airflow via incoming wind and higher fan RPMs. If there is any doubt that the radiator could be the issue, replace and reinspect.

If you have access to a scanner you need to check to see what reported ECT temps are at prior to replacement of any obvious bad items.

Additionally, check to see if there is coolant loss at the overflow reservoir. If there is, that is a considerable red flag and at that point you may want to consider doing a cylinder leakage test. How many miles do you have on it?

 

Get a flash light and check for debris between the ac condenser and radiator. Could be partly blocked with a plastic bag or other things, also you might be surprised at how much stuff will come out if you reverse blow (with compressor) air thru the radiator and AC condenser. They pick up a lot of small crap. But best thought is fan clutch.

P.S. also radiator cap may not be holding the correct pressure.

 

you actually have to check the resistance. stop the truck and grab the fan with your hand, should have resistance

 

I’m having the same problem, but how much fan resistance is normal? I can spin the fan with one finger by resting it on there
I am also losing coolant - 2006 225k miles

 

Check for leaking head gasket.

 

Last thing I need is to replace that

 

Following up - it was the fan clutch. Easy $60 fix.

 

Gives me hope. just bought a thermostat, fan clutch, and water pump today

 

4.0?
What’s the build date?

If 12/05 or before, it’s a 4.0, and it’s overheating = head gaskets*

*Confirm w a qualified mechanic.

 

Fan tests

1. Some people stick their hand in the fan while it's running and see if they can easily stop the fan.
2. Some people stick a rolled up newspaper in the fan to see if they can easily stop it.
3. Some people shut the engine off and see if the fan continues to spin after the engine stops.

If you slice your fingers off, it's not my fault.

 

How am I supposed to know the date of when the engine was made