Fan Clutch Troubleshooting

[NMC_EXP]

Let's start by checking how hot that crossover and heater hose are getting. That will narrow down where to look next. Should take 15 minutes or so.

Enjoy the anniversary celebration!

scottladdy

Still had some light so I ran the checks you described.

The vehicle had been sitting outdoors for (4) hours since being driven. Air temp = 25°F.

Started it and let it idle. Within 5 min. the crossover was noticeably warmer. The heater hoses warmed up as well.

The crossover got progressively warmer. After 20 min. it was uncomfortably warm/kinda hot. Both heater hoses were warm, the lower radiator hose was warm, the upper radiator hose was still cold after 30 minutes of idling.

The heater hose coming off the crossover felt much cooler than the crossover. This makes sense - aluminum is an excellent conductor of heat - rubber is a lousy conductor. Prior to this I believe I've been feeling the heater and radiator hoses, not the crossover and may have been getting fooled about the temp.

The heater hose coming off the crossover goes into the bottom of the heater core - that's as it should be best I can tell from the -20 diagram.

Regards

Jim

 

[scottladdy]

How a thermostat works ...

doghead and scottladdy

If the new thermostat was installed upside down would it act as though it were wide open all the time?

Regards

Jim

I don't believe it would. The thermostat is a valve that is either closed or open.

Now, upside down is a relative term.

There is the orientation parallel to the axis in which there is a cone shaped end and a plug shaped end. The plug is sometimes referred to as a wax motor, as there is a temperature sensitive wax contained inside. As the wax heats up it eventually melts and expands, causing the plunger to push against the return spring and open the valve. When it cools down the wax contracts and the return spring pushes the valve closed. It is vital to have the wax motor in contact with the hot side of the coolant. In the case of our engines it is inserted into the crossover. Failure to do this can result in an overheated engine, which is clearly not your symptom.

The other orientation is perpendicular to the axis. Depending on the manufacturer of the thermostat there is usually some form of small opening or depression or jiggle pin in the valve designed to allow air to pass by the thermostat when it is closed. When the thermostat is mounted with the axis horizontally, as is the case with our trucks, this small opening must be oriented at the top when installed. If this is not done air can be trapped behind the thermostat which would prevent the heated coolant from hitting the wax motor and potentially causing overheating. http://www.stant.com/repository/files/Basic Thermostat Instructions1.pdf

See where this is going?

Thermostats can and do fail. Brand new thermostats can fail. And unless you have a purposely designed "fail safe" thermostat they can fail in either the open or closed position. They usually fail in the closed position due to the powerful return spring. But, if they fail in the open position coolant will always flow through the radiator whether the engine was hot or cold.

I'll let you guess what the symptom(s) would be if the thermostat fails in the open position ...

Interesting Factoid: Traditionally thermostats have been primarily installed in the outlet from the engine. However, many newer engine designs are adopting the placement of the thermostat into the return inlet from the radiator. In these days of ever increasing pollution and fuel economy mandates, manufacturers have learned that they need to keep much tighter reigns on the operating temperature of the engine. Managing the amount of returned cooled coolant allows much tighter control of the engines temperature.

 

[scottladdy]

scottladdy

Still had some light so I ran the checks you described.

The vehicle had been sitting outdoors for (4) hours since being driven. Air temp = 25°F.

Started it and let it idle. Within 5 min. the crossover was noticeably warmer. The heater hoses warmed up as well.

The crossover got progressively warmer. After 20 min. it was uncomfortably warm/kinda hot. Both heater hoses were warm, the lower radiator hose was warm, the upper radiator hose was still cold after 30 minutes of idling.

The heater hose coming off the crossover felt much cooler than the crossover. This makes sense - aluminum is an excellent conductor of heat - rubber is a lousy conductor. Prior to this I believe I've been feeling the heater and radiator hoses, not the crossover and may have been getting fooled about the temp.

The heater hose coming off the crossover goes into the bottom of the heater core - that's as it should be best I can tell from the -20 diagram.

Regards

Jim

OK, so those heater hoses should be getting pretty warm to the touch, especially the one attached to the crossover. Remember, there is nothing preventing the flow of coolant through your heater core when the engine is running. So, if both are nice and toasty you have plenty of heated coolant flowing through the core. If the fan is off, both hoses should feel close in temperature. Is the tank on the passenger side of the radiator getting hot as well? It will heat up from the coolant from the heater core as the return path is through that tank and back into the engine via the lower radiator hose.

If they are not getting nice and hot, there may be a restriction preventing the flow of coolant. Back to Doghead's recommendation to check the condition of your heater core. It may be plugged with corrosion and not allowing enough coolant to flow through.

If they are nice and hot, then we should look at the air mix door and controls. Maybe the fins on the core are plugged with debris and preventing air from passing through.

Your upper radiator hose remaining cold indicates that your thermostat hasn't opened up. These engines take a long time to heat up. Diesel combined with a lot of coolant ...

 

[Skinny]

Wow...talk about rocket science here. The OP originally stated the hoses were cool after the engine was run up, now they are warm and now we are discussing axis of operation. How about if the the rotation of the planet in addition to the jet stream is causing this? After three pages of discussion have we even got an IR gun or thermometer reading. Certainly would be helpful to know if the hoses are hot or cold before trying to e-diag your truck.

 

[NMC_EXP]

Wow...talk about rocket science here. The OP originally stated the hoses were cool after the engine was run up, now they are warm After three pages of discussion have we even got an IR gun or thermometer reading. Certainly would be helpful to know if the hoses are hot or cold before trying to e-diag your truck.

Skinny -

I'm ignorant in many areas and I know it. Unlike most in that category I'm willing to ask questions and learn. However, I am not willing to go out and buy an IR thermometer for this little problem.

If this thread is causing you a bunch of heartburn just ignore it.

Regards

Jim

 

[Skinny]

It's just about getting the facts straight to help you or anyone else having the same issues. Unless you are positive your hoses are hot or cold and have a good temperature reading, no one here can help you and it confuses others. You will spend far less money buying an IR gun to diag the problem (which is great for lots of other things) than throwing parts at the truck hoping it fixes the problem. Only reason I suggest that is because the lack of hard data so far causes me to think you are on that path.

 

[doghead]

Actually, some IP guns are really inexpensive(HF), and really useful for alot of things. I use mine often.

I always have it and use it at every fuel stop, to check my tire temps when towing and trailering.

Warning, never point it at your wife's ear and tell her it is an IQ meter. Just trust me on this.

 

[scottladdy]

Warning, never point it at your wife's ear and tell her it is an IQ meter. Just trust me on this.

 

[NMC_EXP]

It's just about getting the facts straight to help you or anyone else having the same issues. Unless you are positive your hoses are hot or cold and have a good temperature reading, no one here can help you and it confuses others. You will spend far less money buying an IR gun to diag the problem (which is great for lots of other things) than throwing parts at the truck hoping it fixes the problem. Only reason I suggest that is because the lack of hard data so far causes me to think you are on that path.

Your concern about incorrect info makes sense. I am not convinced about my need for an IR gun.

To backtrack - my initial reason for posting this was to get info on fan clutches to help me do the troubleshooting. The observations I reported initially were quick & dirty and misleading. The thread evolved into a full blown long distance diagnostic mostly on cabin heat. That is not what I intended but I am grateful for all the help I can get anyway. Like I said I am as ignorant as a box of rocks.

Here are the latest, correct observations w/o using an IR gage:

--the fan clutch has a bi-metal spring so it is a thermal type.

--with engine cold the fan can be turned by hand with very little effort. The fan does not freewheel and there is no sign of fluid leakage, no fan wobble or noise.

--after idling for 10 minutes at 25°F ambient the crossover is very warm, and both heater hoses are warm, the right radiator tank is warm, the left rad tank and upper rad hose are cold.

--after idling for 10 minutes, best I can tell the fan is pulling just as much air as it did when cold started.

What I've read indicates that a on a cold start a thermal fan clutch will be engaged and moving a lot of air because of fluid settling when the engine is off. Spinning a while will redistribute the fluid and the fan speed will be reduced until the air coming thru the radiator gets hot enough to work the bi-metal spring and fan speed will increase. I do not have a tach to put on the fan to know for sure.

My primary concern was not cabin heat but whether or not the engine was being over cooled. The more I think about this it seems the only way the engine could be over cooling would be no thermostat or a thermostat stuck open. If the fan clutch stuck in the high speed mode that would not matter if the thermostat was working.

From here:

1. I need to install a coolant temp gauge to know whether or not it is cooling properly.

2. I need to check the heater core air control door and blow the dirt out of the core.

3. Both heater hoses are warm so there is some circulation. Would not hurt to flush the core anyway.

If anyone has additional input, I'd be glad to hear it.

Regards

Jim

 

[NMC_EXP]

Warning, never point it at your wife's ear and tell her it is an IQ meter. Just trust me on this.

Good one.

Jim

 

[scottladdy]

Insufficient Heat Diagnosis Flowchart

Skinny -

I'm ignorant in many areas and I know it. Unlike most in that category I'm willing to ask questions and learn. However, I am not willing to go out and buy an IR thermometer for this little problem.

...

So, here is how GM instructed it's service technicians on how to diagnose insufficient heat being generated to warm up the cab for all 1984 truck models.

View attachment X8432_1984_GMC_Light_Duty_Trucks_Service_Manual Page 71.doc

You will note the use of a 220 degree thermometer to measure the air output at the dump door.

You will also note that they recommend feeling the temperature of the heater inlet and outlet hoses, no remote IR thermometer required.

While I do personally own one and do believe it would make diagnosing this issue much faster and easier, it is not required to determine the cause of the OP's issue.

...

If this thread is causing you a bunch of heartburn just ignore it.

Regards

Jim

I couldn't agree more. I am not intending to create a posting firestorm here, but stating my perspective that we need to remain civil in dealing with each other, especially when we disagree with what any of us may be posting in an effort to assist another member.

One could easily see that Jim was feeling a good deal of anxiety with his issues. He was concerned, possibly scared that a significant and costly issue was occurring with his truck, and clearly getting confused with his diagnostic analysis providing symptom descriptions that were contradictory.

As a systems engineer I recommended a reasoned methodical approach to resolving this issue, which is clearly in line with GM's diagnostics flowchart. I was not the one who suggested the following as an impossible root cause to Jim's issue:

... It sounds like the engine can't generate heat at this point.

And in regards to the "operation axis" commentary, the OP asked a legitimate question to which a detailed and accurate answer was provided. An answer that may just assist another member in the future with a similar concern. Why should this cause angst with anyone?

Let's keep the dialogue civil and fact based please ...

 

[NMC_EXP]

One could easily see that Jim was feeling a good deal of anxiety with his issues. He was concerned, possibly scared that a significant and costly issue was occurring with his truck, and clearly getting confused with his diagnostic analysis providing symptom descriptions that were contradictory.

As a systems engineer I recommended a reasoned methodical approach to resolving this issue, which is clearly in line with GM's diagnostics flowchart.

scottladdy

Now you have insulted me by your characterization of me as anxious and scared - where in **** does that come from?

I do regret providing a less than perfect set of observations regarding the state of the cooling system. In my own defense, all I was looking for at that time was info on the fan clutch.

And for what its worth, I'm an engineer myself. My troubleshooting skills saved Caterpillar Inc. millions in warranty reductions, cost reductions and cost avoidance. I may be an engineer but I am not a mechanic, and I know it.

The thing is, a person must know the basic info before he can proceed. I started the thread to learn about fan clutches, and you pretty much ignored that request. Not to say the info you provided was not worth knowing.

Regards

Jim

 

[scottladdy]

Your concern about incorrect info makes sense. I am not convinced about my need for an IR gun.

To backtrack - my initial reason for posting this was to get info on fan clutches to help me do the troubleshooting. The observations I reported initially were quick & dirty and misleading. The thread evolved into a full blown long distance diagnostic mostly on cabin heat. That is not what I intended but I am grateful for all the help I can get anyway. Like I said I am as ignorant as a box of rocks.

Here are the latest, correct observations w/o using an IR gage:

--the fan clutch has a bi-metal spring so it is a thermal type.

--with engine cold the fan can be turned by hand with very little effort. The fan does not freewheel and there is no sign of fluid leakage, no fan wobble or noise.

--after idling for 10 minutes at 25°F ambient the crossover is very warm, and both heater hoses are warm, the right radiator tank is warm, the left rad tank and upper rad hose are cold.

--after idling for 10 minutes, best I can tell the fan is pulling just as much air as it did when cold started.

What I've read indicates that a on a cold start a thermal fan clutch will be engaged and moving a lot of air because of fluid settling when the engine is off. Spinning a while will redistribute the fluid and the fan speed will be reduced until the air coming thru the radiator gets hot enough to work the bi-metal spring and fan speed will increase. I do not have a tach to put on the fan to know for sure.

My primary concern was not cabin heat but whether or not the engine was being over cooled. The more I think about this it seems the only way the engine could be over cooling would be no thermostat or a thermostat stuck open. If the fan clutch stuck in the high speed mode that would not matter if the thermostat was working.

From here:

1. I need to install a coolant temp gauge to know whether or not it is cooling properly.

2. I need to check the heater core air control door and blow the dirt out of the core.

3. Both heater hoses are warm so there is some circulation. Would not hurt to flush the core anyway.

If anyone has additional input, I'd be glad to hear it.

Regards

Jim

Spot on! (or close enough)

The fact that your upper radiator hose and left radiator tank are cold when the crossover is hot indicates the thermostat is remaining closed. Take the truck for a long drive with the cardboard in place to see if the upper hose gets hot, which would indicate the thermostat is at least opening. While I advocate a coolant temperature gauge, it is not absolutely necessary.

Now

 

[Skinny]

Wowser...this is starting to really heat up...pun intended.

I agree, now with some more consistent solid data, do a new thermostat. While your coolant is drained, backflush your heater core. I think you will have positive results.

Don't take anything personally, this is the internet. I wouldn't say you are incapable or ignorant. You are trying to fix something on your own instead of writing a check.