Overheating with AC on in Low Speeds

Maintenance/Repairs
,
21

I am not familiar with your vehicle but just some thoughts and info I have found. I believe your vehicle has a thermal clutch fan. it is possible it is going again. at highway speeds an a/c off there is enough wind blowing through your radiator to cool the engine. but when the a/c is put on it seems the fan is not engaging or not up to what it should be to cool the engine and overheating.
was the water pump changed when they replaced the clutch fan? if not it should have been.

Thermal Fan Clutches

Thermal Fan Clutches are a little more sophisticated in operation than non-thermal fan clutches. The thermal clutch responds based on temperature changes within the engine bay. Using a bi-metal thermostatic coil they sense the engine bay temperature and engage or disengage the fan from the water pump shaft. When engine bay temperatures are cold, the fan clutch is disconnected. As temperatures rise and reach a set point temperature, the bi-metal coil engages the clutch and the fan spins, cooling the engine. Likewise, as temperatures move lower, the clutch will disengage reducing drag on the engine when the fan is not needed.

As the vehicle travels down the road, the temperature of the air coming through the radiator passes over the bi-metal thermal spring located on the front of the thermal fan clutch. The bi-metal thermal spring expands or contracts with the changes in air temperature, which move a valve inside the clutch. When temperatures are cool, this valve is in the position to allow silicone fluid to be pumped away from the working area of the reservoir, allowing the fan clutch to free wheel. When temperatures are hot, the valve is in the position to allow silicone fluid to be pumped into the working area of the reservoir, engaging the clutch and the fan. As the fan speed comes up, cool air is pulled faster over the radiator, cooling the engine and the coolant temperatures. This cycle of engaging the clutch as needed continues.

The Thermal Fan Clutch is engaged at startup because a non-spinning thermal clutch will drain the fluid into the working area of the reservoir. When the clutch begins to spin, the pumping action of the clutch in itā€™s cool state moves the fluid way from the working area until the valve moved it back.

Benefits, drawbacks and key points about Thermal Fan Clutches:

Controls fans speed based on temperature
When at high speed, the Thermal Fan Clutch can provide high speed operation provides maximum cooling with it may be needed.
When engine speed is low, the fan may be disengaged if not needed, providing fuel savings and noise reduction. Again, tied to temperature rather than shaft speed.
Thermal fan clutches have a greater life expectancy than a non-thermal clutch
Thermal fan clutches are briefly engaged at cold start-up
Thermal Fan Clutches engage at about 170Ā° radiator air temperature, which translates to about 30Ā° lower than the actual coolant temperature.

Overheating Engine Temperature Symptoms of a Worn / Defective
Fan Clutch that should be Replaced

How do you know when your Fan Clutch is wearing out or has failed to do itā€™s job? There are a few key symptoms.

Excessive Free-Wheeling when spun manually (when engine is stopped) - With the engine stopped, manually spin the fan. If the Fan spins excessively, over 3 revolutions, as though there is no resistance it should be replaced.

If your air conditioner does not perform well at idle or low vehicle speeds, then the clutch may have failed, and air is not passing over the A/C condenser efficiently enough to cool the refrigerant.

If the fan speed does not increase when engine is running hot or if the fan speed does not increase until engine is excessively hot.

Looseness of the Fan - Excessive lateral movement of the fan blades. If the fan blade moves more than 1/4" front to back measured at the end of the blade. Some lateral movement is a normal condition due to the type of bearing used in fan clutches. Approximately 1/4" (6.5 mm) maximum lateral movement measured at the fan tip is allowable.

Vibration - Sometimes vibration can be detected due to a failed clutch. The vibration can increase with engine speed. Many times this can lead to water pump failure.

When the engine is stopped, turning the fan blade manually turns rough, grinding or does not turn at all.

Leaking silicone Fluid - Excessive fluid leakage will cause the clutch to fail to engage.

Noise - If you hear excessive fan noise or a roar at all engine speeds. Noise can be detected when the clutch should be engaged, during initial cold startup or when the engine is hot. Under high speeds or higher RPMs over 2500, a locked-up fan can create a roaring noise.

When the Fan Clutch Wears and Fails

An important factor when you look at the Fan Clutch is to note that the fan clutch and water pump share a common shaft. Thus, the operation of one will affect the operation of the other. For instance, if the fan clutch bearing wears, then the fan clutch will wobble. The vibration of a wobbling fan will in turn cause the water pump bearing to wear pre-maturely and eventually fail itself. Likewise, a worn water pump bearing can cause a fan clutch bearing to fail for the same reason, vibration being transmitted from one bearing to the other. When replacing the damaged water pump, it is wise to replace the worn fan clutch at the same time otherwise the new water pump will soon fail. That is why the fan clutch should be replaced when a water pump is replaced.

22

Thank you very much for all this info. I really learned a lot through this. I just dropped it back off with my mechanic and he mentioned some of the ideas that are mentioned on this thread. He is going to try to do some extensive testing to recreate the problem. This is great food for thought for me going forward for how a mechanic can have the right ā€œorder of operationsā€. While Iā€™m not sure if itā€™s something he should have done with the fan clutch, I do know that they seem to try their best to triage the problem accordingly. They seemed to assure me by doing the thermostat (which needed to be done anyway) and the fan clutch, that they were following the right order of operations. I believe they told me that they observed it not spinning properly, if at all. So just a little added insight. I donā€™t completely always understand the rhyme or reason for things but I know that this shop is reputable and tries to do things for the best of the customer. However, I super appreciate this perspective. Good to know going forward. Thanks again!

23

But are they really as well informed about air conditioning as a dedicated AC shop would be ?

1 Like
24

touchƩ____

25

Hi again everyone, I have an update on this issue in my continuing saga to resolve this issue. Thank you to everyone for helping me to this point. Itā€™s really been valuable to me. Last Friday my mechanic replaced the water pump and timing belt. They assured me the issue with the temperature rising was fixed. I brought forward some of the suggestions with cleaning the radiator, AC compressor, etc. However, they felt strongly the water pump was the next step. In trusting that they were the professionals, I let them do their thing. On Friday when I drove it home, the temperature was holding firm in the middle for about 15 minutes. This was on a rural road of speeds of around 50 mph. During this time the AC was on full blast. I wanted to give it a good stress test. As soon as I got into town and stopped at a stop light, the temperature started to climb. I started to get anxious and called my mechanicā€™s office. He seemed a little nonchalant (although it was the 3rd time in a couple weeks I had brought it in) and told me that he test drove it and that it was fine after the repairs he made. He made mention to how he had even left it in idle for an hour and that the temperature had climbed ā€œand then went back downā€. I was still on the phone with him and a little anxious so I started driving again and it went back down to middle temperature as soon as it started accelerating above about 30 mph. I decided to give it a thorough test drive and see if I could see any patterns before contacting him again. It appeared that after driving for periods of 15 minutes or so and then coming to intermittent stops that it would start to rise. However, shortly after accelerating the temperature would fall to middle again. Iā€™m sort of at a place where I feel I need to regroup and get a new strategy. I left a message on my mechanics machine on friday evening thinking he would have the concern to call me back and he hasnā€™t. So I guess my question is this. Do you think that itā€™s significant enough of an issue that this can cause eventual damage to my engine? Should I try to take it to a new mechanic that could try some other things? It just seems to me like he is overly busy and wanting me to be content with a half hearted job. This situation matters enough to me to want to see it to completion but if itā€™s one of those things that I just gotta live with then it is what it is. Thank you all so much.

26

Take it to an actual air conditioner shop . You are not happy with this shop and I donā€™t think they really want to solve your problem .

2 Likes
27

Thanks for the honest feedback. I donā€™t recall seeing many shops that advertise as an AC specialist. Do you mind giving me any search phrases to start my search? I tried asking on next door as well so weā€™ll see if people can help refer me locally. Thanks so much!

28

An air conditioning shop for a cooling system or engine repair? An air conditioning shop might replace the radiator and fan but may not want to get involved with engine repairs.

29

Okay, good to know. I guess Iā€™m a little uncertain as well on whether I should go to an AC specialist if there are still things to try that a general mechanic can do. So would it make more sense to just set the expectation with the new mechanic that if itā€™s AC related and they donā€™t have the expertise to fix it, then to refer me to an AC specialist?

30

An air conditioning shop is a general auto repair shop that has technician(s) that are trained and certified to work on automotive air conditioning.

Iā€™ve been a trained/certified automotive AC technician since 1993.

But I use to do all other automotive service repairs.

Tester

31

We have cabins in the north woods. I called the NAPA parts place and asked for a mechanic recommendation. They fixed a wheel bearing than a couple years later recharged the AC put in dye and said we will see what happens. ended up being a leak in the condenser. Could be transmission overheating, who knows, but a good shop would serve you better, my thought,

32

Itā€™s critical the cooling system hold pressure correctly. Most shops have a gadget that screws onto where the pressure cap usually goes, then they pump it up to a pressure similar to the pressure capā€™s rating, then monitor the pressure to make sure it doesnā€™t drop more than one or two psi over the course of an hour. They also test the pressure cap separately. Has that all been done?

If so, and now water pump has been replaced, and you are certain the engine compartment fans are spinning the correct speed, moving the designed amount of air, the next step if you feel the cooling system still isnā€™t working properly is probably to replace the radiator. Iā€™s a 20 year old aluminum radiator, so will probably need to be replaced pretty soon in any event b/c it is bound to spring a leak. Canā€™t speak to your car/engine, but on my Corolla, the coolant temp rises from ambient to mid-range and pretty much stays there when driving. On long idles it goes up a little, then the fan turns on and it comes back down. Up and down like that on long idles. But it doesnā€™t do that when driving. Same for my truck, when driving pretty much stays at 180-190 degrees. But when driving very slow, like in 4WD, or idling it will climb to 210 or so. It has no electric fan, only the engine driven fan.

My guess, something is still preventing the cooling system from maintaining the designed pressure. The pressure cap has already been replaced I presume. I was having a little overheating on my truck last year, new pressure cap fix it straight-away. A visual inspection w/magnifying glass showed the seal was obviously deformed and cracked. Sometimes the cap is ok, but the surface it seals too is corroded or warped, so good idea to check that.

33

Thank you for this perspective. I have now driven it for about 10 days since my last mechanic trip. The temperature gauge has been in the middle at all driving modes. Only when I turn on the AC and either drive up hills or stop after long stretches of driving does the temperature rise. So I have pinpointed the issue to the AC it seems.

34

Thank you for this perspective. I have now driven it for about 10 days since my last mechanic trip. The temperature gauge has been in the middle at all driving modes. Only when I turn on the AC and either drive up hills or stop after long stretches of driving does the temperature rise.

Thank you for the info on your vehicles. I am curious if the radiator or AC has something to do with it. I mentioned some of the things you brought up in the thread and my mechanic discarded the AC compressor and didnt want to entertain the radiator. Didnt even mention anything. He almost acted like the trail was cold. He basically tried to convince me that the gauge will go back down when you accelerate and that cooler weather is coming. If thats the reality, then he could tell it to.me straight and give me my options. But just felt like he wanted to be done with me and not go any further into diagnostics. I will say though, regarding the radiator, I spoke with a new mechanic and told him my radiator was replaced around 40-50k miles ago and he said it would be rare that a radiator would go bad at that age. But he said he would test it. So anyways, thank you and I know Iā€™ll get to the bottom of it at some point.

35

Unlikely a relatively new radiator like that would be clogged up enough to prevent correct cooling. But it would still a good idea to pressure test cooling system. A cooling system pressure test, it tests more than just the radiator. Coolant hoses, head gasket, water pump seal, and pressure cap etc are also tested.

36

Okay, thank you!

37

Are you suggesting there is a coolant leak?

The radiator has poor flow, this causes poor heat transfer, and the fan clutch is not reaching the temperature necessary to engage. When the engine is operating at a higher than normal temperature, raise the hood, elevate the engine speed to 1500 RPMs, the radiator fan should be locked and at full blast. This will be loud and forceful.

38

My guesses are either cooling system not holding pressure correctly, or head gasket problem.

39

I looked up some info online about head gasket symptoms and checked a few things. Many people said you may notice oil/discoloration in the coolant tank and radiator. Also a lot of exhaust coming from the tail pipe. I havent seen either of these symptoms so my hope is that its not that. Just out of curiosity what are your thoughts on whether I should replace the head gasket if it is the issue? Iā€™ve heard its very expensive. I guess I may have to decide whether the other potential issues it has are also worth the cost of fixing. To be forthcoming, the catalytic converter is bad and probably will need a new battery. Although where I live I dont need to pass emissions. So If it is the head gasket I will have to put a lot of money into it in addition to the head gasket. However, I probably wont be able to sell it for very much and will have to pay more for a newer used car. It seems to run smooth and the transmission was replaced 30K miles ago. So it has that going in its favor. And I will say, id rather have a used car thats paid off and just expect to see the mechanic at least every and maybe even pay several hundred per year in mechanics fees. I know this is kind of preemptive considering I wont be taking it in to the mechanic until the 14th and I dont know the actual issue yet. However I just want to get some thoughts on whether it makes long term sense to fix it.

40

Has anyone in this long odyssey actually measured the actual temperature that the coolant is reaching when the gauge rises?