Idling + AC = overheating?

[Raymond]

Hi all. Back again with more trouble with my 88 MGM.

Today, a friend of mine was stuck on the side of the road with a flat so I show up to help. It was 90+ degrees today so I left the car running with the air on for him so it would be cool since he had been out there on the highway for several hours. I jack the car up and take the tire off, and when I get back to my car the red Check Engine light is on. I about soiled myself. I figure "let's see if I make it home" but as soon as I pulled onto the highway and drive off, it went away.

We get back there, and I do the same thing: leave it idling while I put the tire back on. And the light comes back on. Now, I now my way around a wrench to some degree so I make the correlation between sitting there and the light since it never happened before.


I did some digging when I got home and I guess that a common thing with the box is overheating with the AC on at idle. What I didn't find is a good solution for this. My box seems to have a good old fashioned mechanical fan attached to the crank pulley. Now, thankfully I don't think I did any damage. I had to jump his car (dead battery from hazards) and when I popped my hood with the car running I didn't detect any of the death signs of overheating such as boiling coolant, steam, or white smoke from tail pipe (aluminum Honda four bangers have done this to me; they are not tolerant of heat and like to pop head gaskets if run hot). She's running fine as well.

So since there isn't an electric fan for me to replace, what are some ways to get around this? I topped the radiator off after doing the heater bypass hose thing a few days ago and thought I let all the air bubbles out by running it to normal temp with the cap off. Should I replace the cap? Are there better radiators out there than what may or may not be the original? Does this happen with JUST the AC on, or do you think it will do it with any extended idle, AC be damned? I'm not a princess so I'm willing to shut it off when I'm stuck in traffic. That has me worried the most. I commute from IL to MO every day and sometimes can get stuck sitting.

Thanks for reading my bullshit. Look forward to seeing what I will be added to the to do list next.

[jaywish]

First suspect is the fan clutch.

Get someone to help you. Stare at the spinning fan on the fully warmed up and running engine. Have helper turn off the engine. If the fan freewheels more than 1 revolution it is shot. Buy & install a new thermal fan clutch.

[DerekTheGreat]

What kind of shape is your coolant in? My TC never has an issue with overheating but Ashley's does. If the coolant is never changed it gets skuzzy and then that in turn eats radiators, heater cores, water pumps and thermostats. Ash has a new radiator & thermostat and as long as she's moving a long and its below 80 degrees outside she's fine. But if her car sits we can watch the gauge climb, especially with the A/C on. We figure it could benefit from a new water pump but until it loses a few more legs we're going to keep it right where it is. AFAIK the cap just vents excessive pressure, so if you notice the overflow bottle's level is higher when hot and lower when cool I'd say that's working good but if it's spring is all rusty and gunky you could replace it. Also, if your radiator is in good shape I'd look into the thermostat or water pump or both.

[Raymond]

Not so sure on the coolant. It could probably use a drain and refill since its the coolant that was in the car when I bought it a month ago and there's no telling how old it is. On the same coin, there's also no telling how old the existing radiator, hoses, and t-stat is. I will plan on changing the radiator, t-stat, and new coolant soon. I drove to work today, sat at a bunch of stop lights and no issues. I don't know how long exactly I was sitting on the side of the road since time flies when you are doing work.

[jaywish]

Derek,

Did you check the clutch?

[Raymond]

So I'm doing some research and found some listings for Thermal Fan Clutch. Such as this one:

http://www.oreillyauto.com/site/c/detail/MOT0/YB328/03389.oap?year=1988&make=Mercury&model=Grand%2BMarquis&vi=1199471&ck=Search_fan+clutch_03389_1199471_992&keyword=fan+clutch&pt=03389&ppt=C0331

Forgive my ignorance but what exactly is the different between a Thermal Fan Clutch and a non-Thermal Fan Clutch? From looking at my car last night (in the dark with a flash light) and this, it appears to be fairly simple to replace, no?

EDIT
I'm reading this now on the differences.

http://www.haydenauto.com/featured%20products-fan%20clutches%20and%20fan%20blades/content.aspx

[jaywish]

Good article on the difference. It is a reasonably easy job. I don't recall needing to take out the rad but the shield can be a bit of a PITA.

Make sure the engine is hot, probably best with AC on to heat it good to check the clutch.

[Raymond]

Thanks a bunch guys. I'm at work but tomorrow I will go for a cruise with the misses and when we get home I will check it out and start there. Seems less labor intensive than the whole radiator and T-stat. Those I will surely just do anyway at some point just so I know when they were replaced and that they are good. The upper rad hose is a Motorcraft one and looks a bit swollen so who knows when any of it was last done (if ever).

[gadget73]

Another quickie to check is to make sure there isn't a blanket of garbage on the front of the radiator. I've seen things that looked like the lint filter in a clothes dryer before. A quick shot with the hose to flush any such garbage out is usually not a bad idea. Make sure you get between the radiator and the condensor too. What you can see from under the hood is the AC condensor. If a critter built a nest between the two it will block off airflow considerably. You can get to the radiator front by shooting a hose between the rad support and the top edge of the radiator itself.

If all that is good, you may just need a radiator. The tubes crust shut over time if good clean water isn't used.

[88Vic]

Until you fix it and you want to leave it running with a/c on again, open the hood to let heat vent out. Also you can get a lower temp t-stat if you live where it gets very hot very often.

[DerekTheGreat]

Derek,

Did you check the clutch?

I have not.. I don't know anything about how those fans work and I saw that hers was spinning (and doesn't make noise & need oiling like mine does) so I figured it was all good. Guess I need to read up on how to check those things.

Another quickie to check is to make sure there isn't a blanket of garbage on the front of the radiator. I've seen things that looked like the lint filter in a clothes dryer before. A quick shot with the hose to flush any such garbage out is usually not a bad idea. Make sure you get between the radiator and the condensor too. What you can see from under the hood is the AC condensor. If a critter built a nest between the two it will block off airflow considerably. You can get to the radiator front by shooting a hose between the rad support and the top edge of the radiator itself.

If all that is good, you may just need a radiator. The tubes crust shut over time if good clean water isn't used.

Thats a good point too, I had a Ranger with A/C that didnt work once. Couldn't figure out why but when I took the radiator off there was tons of garbage & old moldy leaves inbetween the radiator & condensor. Engine never ran hot but when I cleared the crap away, pow, working A/C.

[86VickyLX]

Probably the fan clutch. If you warm up the engine and then shut it off, the fan should immediately stop spinning. If it continues to spin after the engine is off, the clutch is bad.

[DerekTheGreat]

Thanks John, I'll check that today!