92 Q Running Hot Hot Hot With AC On!

[Jesda]

Got out of the car, hit the remote start and left the AC on to keep the interior cool, and went into the grocery store. Five minutes later, I came out and got in, and noticed the temp gauge needle was about 3/4ths of the way up. Usually its right in the middle. Im thinking OH CRAP this whole time.

I opened the hood, the fan was spinning and such. I shut the car off and removed the radiator cap (stood far away and used a golf club to open it.) The fluid looked clean with no signs of rust or anything.

I turned off the AC and drove to my mechanic on the other side of town. It seemed fine, but at stoplights it did run hotter than usual even with the AC off. Typically, the temp needle is in the center at the 3 oclock position.

So tomorrow morning at 7:30am I'm going to drop the car off and have the folks at the shop look at it. He said the AC might have been overcharged causing the AC to work to hard and making "head pressure" to be too high? Or perhaps the cooling system is clogged somewhere, or the AC system is clogged.

Anyone have a hunch! Thanks in advance.

-Jesda

[elwesso]

Tstat??? They can fail at will.... It could be partially stuck open, so at least it isnt like completely overheating!!!!

[Jeff Williams]

A lot of times, shops will overcharge the A/C after a compressor change. It really depends on the ambient temp, when they charge it. Some guys just start the A/C, and let her rip. I noticed you just had the A/C repaired. He is probably correct in his assumption.

[Jesda]

Im confused... if the thermostat was stuck open wouldnt that mean that the car would have a hard time getting warm since water and cooling are constantly flowing? Or would that keep the system from building pressure, thus causing it to overheat?

Thank you,

-Jesda

[Q451990]

Or the t-stat could be stuck partially closed. Is your auxilary (electric) fan coming on? Overcharging with freon won't make the system cool better! Yes it can cause higher pressures on the a/c system, but in order to change the temperature on the a/c condensor enough to overpower the radiator it would have to be glowing!!! Besides if it was removing that much more heat, it would cause the evaporator to freeze up.

I'd be much more suspicious of an over tightened or under tightened belt (taken off to r&r the compressor), a bad aux fan motor or disconnected one... etc.

What sort of ambient temperature and humidity were you driving in today? Did they remove the A/C evaporator while working on the car, or just replace the compressor? Any other work at the same time?

Heath

[Jesda]

The big fan is coming on, I can see and feel it blowing. Its been working all day.

I went out for a drive tonight and drove with the AC on and off, and everything worked perfectly. Earlier today it was about 35% humid at 100F, tonight its about 72F with low humidity.

When the AC work was done, they only removed and replaced the compressor and charged the system with R12, without touching anything else.

What is this high "head pressure" that my tech was referring to?

Now I'm really confused.:help

[BadQ45t]

Had the same issue with dad's 92, you may need to core the radiator and probably replace thermostat too, I'd start with the thermo and work my way to a core job.

[Jesda]

What does "core the radiator" mean?

[Q45tech]

Radiators start a progressive decline in efficiency and after 6-7-8 years all the new safety margin is TOTALLY gone from internal and external corrosion. Plus dirt/leaves trapped in front and bent fins on condenser restricting the air flow.

An as new cooling system ususally means all parts are brand new.

In 100F ambient and idling in park [idling in drive is worse a faster due to TC load] you have only so many minutes [in an old used system] before the system loses control and begins to overheat.

Some cars lose it in 5 minutes, some 10, some 20 and some beyond 20 minutes without air flow from speed.

There are were foam surrounds at the radiator to avoid air leaks around the radiator these fail with age.

Overheating is dangerous to the life of an all aluminium engine since aluminum alloys are very sensitive [structural changes] to temperatures above 300F. Not to mention it causes a $1,000 bill for melted/cracked knock sensor replacement.

Overheats, chain guides, and poor oil change habits are the causes of engine destruction.

[Jesda]

Thanks for the info Dennis and everyone. Looks like I'm looking into a theromostat at minimum, and a radiator to be safe. Fortunately after getting laid off I'm due a huge severance check.

Quick question... at what point on that temp gauge does it reach 300F? 3/4ths of the way up?

Thanks,-Jesda

[Jeff Williams]

That temp gage is about as accurate as a 100 MPH speedometer on a bicycle. Don't rely on it, if you know you have overheating problems. (IMO)

[Q451990]

The big fan is coming on, I can see and feel it blowing. Its been working all day.

By the "big fan" do you mean the one you can see (bolted to the front of the engine) or the auxilary electric fan hidden in front of the a/c condensor. Typically, you'll only hear it come on unless you really get down and look for it... it makes enough noise that you'll hear the difference when it comes on.

The mechanical fan has a viscous coupling that lets the fan turn at different speeds according to the temperature. It will turn faster (locked closer to or with the engine speed) when it's hot, and slower when it's cool outside. You'll want to have this checked too. When the car is off, you should be able to spin the fan easily by hand when the car is cold, but have more resistance when it's hot.

Heath

[90Q45blue]

The mechanical fan has a viscous coupling that lets the fan turn at different speeds according to the temperature. It will turn faster (locked closer to or with the engine speed) when it's hot, and slower when it's cool outside. You'll want to have this checked too. When the car is off, you should be able to spin the fan easily by hand when the car is cold, but have more resistance when it's hot.

This is called the "Cooling Fan Clutch". The part is $131.93 from Joe. I too was having a slight overheating problem so I parked the car, had it towed to my mechanic and he diagnosed the problem as a bad thermostat and a bad cooling fan clutch. He is replacing them this week. I'm going to pick up my car in 3 hours. I'll let you know how it turned out.

Nick

[Jesda]

How long would it take to do the radiator if I did it myself? The book quotes 2 hours. Any shortcuts possible?

Money is an issue, but on the plus side I live with a former technician who would help me do it, bringing the total to $0 for labor if I did it at home.

[elwesso]

SEARCH!!! I think its more time-consuming than hard...... and if you have a FSM that will greatly help........

I usually add a 2hours to the book time......... From my lack of experience and i go slow to make sure I do it right......

[Jesda]

Cool. I'll get cracking! Yeah, got the factory manual and it looks complex, but nothing too awful.

Thanks again-Jesda

[Q451990]

Replacing the radiator should be very simple. It's held in place by two brackets under the protective shroud. Then it's just four hoses. Here's a quick step by step:

1-Jack up car.2-Remove finishers from top of radiator area3-Remove road shield4-Remove clip on portion of shroud from bottom of fan opening5-Remove four sheet metal screws retaining shroud to radiator6-Unclip any hoses and electrical connectors fastened to shroud7-Remove shroud8-Remove two 10mm bolts from brackets holding radiator to frame9-Disconnect radiator hoses (from internal OEM cooler or aftermarket cooler, which ever one you have)10-Disconnect upper and lower cooling hose.11-Lift Radiator out.

If by chance you don't have an auxilary cooler for your transmission, now's the time to install it. Order new foam surrounds for the radiator while you're at it - should be less than $10 for both. If you replace the t-stat you may want a new cover, hose for the cover to the metal pipe, and metal pipe - all of which lead to the bottom hose in the radiator. Also if your fan is cracking, you have a lot of room to work on it while everything is out...just don't overtorque the bolts into the fan clutch when reinstalling the new fan!

This sounds complex, but it's really one of the easiest things you'll do! I'd rather do this than an oil change...

Heath

[elwesso]

I may be about ready for a new radiator.........

And oil changes are no fun on the Q....... Nothing like HOT oil running down your arm to get off the filter...... At least if your skinny you dont need to jack up the car to get to the pan drain plug!!

[BadQ45t]

The "core" job I mentioned will make the radiator as good as new, maybe there are some people that do not like doing that, but I've had great luck in making them good as new. This is essentially a removal and complete thorough cleaning done at a radiator shop.

[elwesso]

How much does something like that cost????

[Jesda]

GREAT news! Called around town today and got price quotes for the following:1. Remove radiator2. "Rod out" or "core out" the radiator3. Install radiator

One shop I usually go to wanted $185 with coolant, taxes, etc.Another shop quoted $120 + tax, been in town for decades.

So I think for $120 I'll be good to go. We'll find out Wednesday when I come in for my appointment. Its cheaper than $400 I was about to spend for a radiator, thermostat, and labor. I might do a thermostat anyway and get a couple years out of this radiator.

-Jesda