Overheating issues.

[Troutsrunner]

I noticed yesterday at the drive thru that my engine started to overheat with my ac on. I started driving and the temp went back down to normal at about 195 and then i came to a stop light and it started to overheat again. I put it in neutral and reved the engine to 1500 rpm and the temp quickley went down. Does any one know what this means? Ive checked the fan clutch, i can move it but not freely. Where do i begin checking? Also i dont see any overheating with my ac on. Everything has been fine all summer until yesterday.

 

[the great him]

so you say your fan wont spin? sounds like a bad fan clutch, but other things to check are, coolant level, and or water pump. the pump could be going bad and at slow to no speed the pump cant cool enough by itself so you have to have airflow through the radiator to help. either way what ever this is, you are needing the airflow to help cool things, slow speeds and idle your stock cooling system can not keep up.

 

[BlackCat914]

Yup, sounds like a weak fan clutch.

 

[Troutsrunner]

so you say your fan wont spin? sounds like a bad fan clutch, but other things to check are, coolant level, and or water pump. the pump could be going bad and at slow to no speed the pump cant cool enough by itself so you have to have airflow through the radiator to help. either way what ever this is, you are needing the airflow to help cool things, slow speeds and idle your stock cooling system can not keep up.

Its not that the fan wont spin, it spins when the engine is on but i read somewhere on here that if you can move the fan freely when the engine is off you have a bad clutch. So idk, i just dont want to start throwing money at parts that dont need replacing. My wife just had our daughter on monday and money is slowly getting tighter.

 

[TheDurk]

Its not that the fan wont spin, it spins when the engine is on but i read somewhere on here that if you can move the fan freely when the engine is off you have a bad clutch. So idk, i just dont want to start throwing money at parts that dont need replacing. My wife just had our daughter on monday and money is slowly getting tighter.

You can't tell anything from what the clutch does when it is cold. I had my bad one and my new, good one on the bench and resistance was identical. There is a lot of BS out there on fan clutches. Here is the best thing I have seen, off a BMW board, but it applies to ours:

Fan Clutch Test:

Testing the fan clutch:
If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good indication, if it does not increase speed/noise, clutch is bad and needs to be replaced. (Remember, this must be tested after the car has been off for and extended period, over night etc.)
2. Leave engine running and note if the fan starts to slow down after 2-5 minutes, speed/noise should diminish and even raising the RPM, the fan should not make as much noise as when first starting, if it does slow, this is the second good indication. If speed/noise does not decrease, clutch may be “frozen” and should be replaced.
3. Leave the engine idle and watch the temperature indicator. When normal operating temperature has been reached, some increase in fan speed/noise should be noted, in particular when the RPM is increased. If temperature is fairly stable and the fan noise/speed increases or cycles, third good indication. If temperature indication continues to increase, with no increase in fan noise/speed, clutch is defective and should be replaced.
4. After the engine is at normal operating temperature or above, is the only time that the “rolled up newspaper” test that many people talk about should be performed! Take some newspaper and roll it up into a long narrow tube. Be careful, keep hands and fingers away from the fan while performing this test! With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub. Push the rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.

Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test.
Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches “redline”.

Here is my mini-DIY on the swap; good info elsewhere in the thread, too:

1998 3.4 Auto 4Runner, Overheating Issue, Suggestions? - Page 4 - YotaTech Forums

 

[Troutsrunner]

You can't tell anything from what the clutch does when it is cold. I had my bad one and my new, good one on the bench and resistance was identical. There is a lot of BS out there on fan clutches. Here is the best thing I have seen, off a BMW board, but it applies to ours:



Here is my mini-DIY on the swap; good info elsewhere in the thread, too:

1998 3.4 Auto 4Runner, Overheating Issue, Suggestions? - Page 4 - YotaTech Forums

thanks man great post, i actually have your writeup saved in my bookmark folder, ill test it that way in the morning hopefully its just a bad fan clutch.

 

[MattinLA]

You're all wrong

The fan should not spin freely there is no prob. I say the radiator is clogged. #1 most insidious, difficult to verify problem with overheating engines and a destroyer of head gaskets. THAT needs to be checked FIRST. Get thee to a radiator shop and have it checked IMMEDIATELY.

 

[the great him]

The fan should not spin freely there is no prob. I say the radiator is clogged. #1 most insidious, difficult to verify problem with overheating engines and a destroyer of head gaskets. THAT needs to be checked FIRST. Get thee to a radiator shop and have it checked IMMEDIATELY.

if the radiatior was clogged how do you explain when he is moving the temps drop? that means the radiator is doing its job... radiators need air flow, when they dont get that air flow they will over heat. if the radiator was clogged then it would not matter if he was stopped or doing 120mph in clean air or if he had a giant fan pushing and pulling air over the radiator, it would still over heat...

 

[MattinLA]

No it makes sense completely.

OK radiator blockages are never COMPLETE blockages - until the engine finally fries and dies. It's ALWAYS a partial blockage until it finally blocks totally which is why blockages are the MOST INSIDIOUS and difficult to pinpoint cause of overheating. I had a blocked radiator that did not even show HOT, all I was seeing was water continuously evaporating from the reservoir which was the dead giveaway until the head gasket blew. The radiator may be JUST barely cooling enough water - since the car is moving! But when it stops, you've got a problem!