Fan Clutch or Thermostat?

[Sungod]

Noticed my temp gauge creeping up sitting at a light then heading toward red. I turned the heat on full blast and the temp started dropping close to normal. Got out checked the reservoir and hoses. Everything looked full and tight. Opened the cap a little and had good pressure. Let it sit for a while and hopped back in and the temp settled in its normal spot for a while then shot back up. Got home and opened the hood and though the fan was turning slow. Put a piece of tape on it and started it again and it didn't even break the masking tape. The fan just spins slowly.

I am leaning toward the fan clutch. From what I saw in the FSM, these are fluid clutches that should engage when it is hot. I may just change the thermostat just for fun. Normally when they fail, they fail open. Of course that is normal and my luck is far from that.

 

[Gerdo]

If the thermostat failed open, it would take time to reach normal operating temperature. If it failed closed, it would not cool down as you drive also.

If it's a bad clutch fan, it would heat up sitting. You could also try, in your driveway, let it run and when you see the temp climb blow air thru the radiator with a leaf blower. If the temp drops, I would say it's the fan clutch.

Hosing the radiator down with cool water will also work.

 

[Sungod]

If the thermostat failed open, it would take time to reach normal operating temperature. If it failed closed, it would not cool down as you drive also.

If it's a bad clutch fan, it would heat up sitting. You could also try, in your driveway, let it run and when you see the temp climb blow air thru the radiator with a leaf blower. If the temp drops, I would say it's the fan clutch.

Hosing the radiator down with cool water will also work.

Doesn't the heater bypass the thermostat?

 

[MikeInNH]

Doesn't the heater bypass the thermostat?

How's that possible???

 

[DC runner]

In general, if the vehicle maintains the appropriate temperature while moving; say freeway but overheats at a standstill this is usually the fan.

Except is super hot situations, the movement at 60 mph will push more than enough air across the radiator and engine to cool it down.

 

[black_120]

Yeah, sounds like the fan clutch.

One of my buddies used to use a shop rag to slow the fan down. If it quickly gets back up to speed the clutch is fine. Since yours cant even break a piece of tape, Its safe to say its the fan clutch.

 

[Sungod]

How's that possible???

The thermostat sits in front of the upper radiator hose. The heater outlet is before the thermostat. Coolant doesn't flow through the radiator until the thermostat opens, but it will flow through the heater core.

 

[Sungod]

And the winner was...... The thermostat. It was locked up solid. I boiled in a pan and it didn't open so obviously wasn't opening at 212 degrees. New thermostat installed and the gauge is back to sitting slightly below half way.


I knew I should have replaced it when I did the timing belt and pump, but it was out of stock and didn't feel like driving an extra 2 miles to autozone. One of these days I will learn.

 

[Gerdo]

Nice find.

 

[black_120]

And the winner was...... The thermostat. It was locked up solid. I boiled in a pan and it didn't open so obviously wasn't opening at 212 degrees. New thermostat installed and the gauge is back to sitting slightly below half way.


I knew I should have replaced it when I did the timing belt and pump, but it was out of stock and didn't feel like driving an extra 2 miles to autozone. One of these days I will learn.

Glad to see you got it figured out. Years ago I kept having overheating issues on my 3rd gen. I replaced the thermostat, then the water pump, and then did the fan clutch. It ended up being a bad radiator which was a surprise since I only had 80k on the truck.

 

[Sungod]

Glad to see you got it figured out. Years ago I kept having overheating issues on my 3rd gen. I replaced the thermostat, then the water pump, and then did the fan clutch. It ended up being a bad radiator which was a surprise since I only had 80k on the truck.

Was yours clogged? I did notice a fair amount of build up on the thermostat. I guess this red stuff isn't as good as they make it out to be. I wish now that I had changed the coolant at 50K instead of waiting to 100.