Still working out some of the "bugs" in the 1979 coupe I purchased just before winter set in, after being Vetteless for 10 yrs.
It was 80 degs yesterday, fired the vette up and took here for a 30 mile spin around the countryside.

No problems, except discovered that the AC compressor clutch will not engage. Decided also to check the oil and the radiator afterwards after everything cooled down, oil ok, but the radiator (once I get that pesky rad cap off), was full, but full of what LOOKED like a murky dark orange KoolAide mixture. It didn't overheat or anything, just LOOKS odd to me. The Vette was left covered outside all winter, and nothing "froze", so it must be ok in that respect.

What do y'all suggest, button it up and leave it alone, or drain it and start all over again with fresh water/coolant? Nothing SEEMS to be leaking...at least not obvious.

Any hints or suggestions on something a 'novice' mechanic like myself should look for regarding the AC compressor in getting to clutch to engage? I already had to replace the relay for the fan motor to get that working. When I slide the slider for the AC over to max cool, it does cause the engine RPM's to increase, so at least THAT part of the system seems to be working.

 

Your system needs a serious cleaning, not just simple flush. Parts stores nor GM No longer sell the good stuff (eg prestone AS100 they don't make it anymore). Make your own real simple. I've done it many times. DAP/Savogran wood bleach is oxalic acid and neutralizer is washing soda or baking soda. Think ahead ... through the logistics and practicality of where you do this as there's lots of gallons of nasty stuff coming out (it'll burn a lawn). It's important you Wear eye & hand protection when mixing & handling Oxalic acid & solutions thereof. Also, use that common sense ... don't shock a Hot motor with Cold water ... might save you a few minutes waiting for cool-down but might cost you a motor if you do shock it! Better angels of engineering might shield you on that sometimes; then again ...?

Look to GM TSB 99-06-02-012D for guidance (It's Not about corvette but applies as well) ... go to CF link below look at my post (I recall #17). Use that TSB as guidance. Maybe you have dexcool AF maybe not ... does not matter ... yours needs CLEANING. If yours has a removable overflow/expansion tank ... take it out and clean heck out of it separately. Overall, This is an hours-long procedure if done properly. I begin with a Pre-clean by doing a simple drain and water-only flush ... then I actually begin the procedure following TSB 99-06-02-012D as a guide. It's important that the motor runs a long time to heat & maintain heat to drive the chemical reaction that cleans.

This cleaning is so strong it may damage BOTH your T'stat & Rad Cap ... go ahead & buy BOTH and replace BOTH as you refill system with fresh AF/water.

Buddy, I promise you ... IT WORKS!


https://www.corvetteforum.com/forums...ner-flush.html

 

I'm not going to disagree with jackson, he knows what he's talking about.

I'm just going to add that a combination of Dexcool (orange) and an incomplete flush last time may make your coolant look terrible.

Probably not obvious is that there are two block plugs on the sides of the engine that can (should) be opened up as part of the flushing process, in addition to flushing the radiator. One is just ahead of the starter on the second image below. It helps that my exhaust manifolds were already off the car. I got mine out with a breaker bar, so I consider myself pretty lucky. If you can, do this outside on ramps, as it will make a mess. With the plugs out, you may need to stick a screwdriver in the hole to get it flowing.

You can then flush the block with fresh water through the thermostat housing, before moving on to jackson's cleaning process.

 

I would start with a more conservative approach, as I am concerned using a strong cleaner on an older radiator might cause a leak. The parts stores sell a radiator flush t fitting that goes between one of the heater hoses and hooks to a garden hose. I would take the radiator cap off and start running water thru the system until it is clear. I would then start the car, turn the heater on and run more water thru, until it is clear.

I also do not open the engine drain plugs if I do not know the last time they were opened, as to not risk breaking the head off, while trying to remove it.
I also would drain the water from the radiator by siphoning it out and not opening the bedcock on the radiator, so there is no risk of breakage.
Then fill the system with antifreeze.

Regarding the compressor, the system may be low on freon. I would hook up a set of manifold gauges to check the pressure. If there is some pressure, you can take a short piece of stiff wire and push it into the back of the terminals of the connector, that is plugged into the low pressure switch to by-pass the switch. Put the AC on and see if the compressor engages. Look at the low pressure side of the manifold gauge set, and if it quickly drops below 30psi, the system needs a recharge.

 

There is always the possibility that a internal hole in the Rad is allowing ATF to mix with your coolant. Check the ATF level / color.

 

Sounds like Dexcool sludge.

 

The radiator flushing kit will help clean the sludge out, but it requires you to cut a heater hose and leave a cheap plastic bit in your heater system, or you will need an additional short piece of hose.

Also, unless you either remove the block plugs, or do a final flush with distilled/deionized water, there will be a gallon or two of tap water left in your system. Perhaps that isn't a problem where you live, but I don't even wash my car with the water from my well (fine to drink though!)