I have a 91 Autocoupe with about 25k on the clock that I bought Oct/01 with 16k, I dont think the coolant system has ever been flushed"I never did it in the three and half years that Ive owned it" I just want to know the best flush product and procedure on a flush and fill. Not running hot yet just want to avoid the heat

 

I used to flush mine every two years, with just water. You might start there and look inside when you've done a thorough flush. If in doubt, you can pull it and have it flow tested at a rad shop. My car is 23 years old. It has the original radiator core and it cools like a champ.

RACE ON!!!

 

Checkout the tech tips on this forum for C4. here is one

Coolant flushing tool -- 1 of 1
Date Published: 2003-05-27

Submitter's Name: Tom Strickland
Email Address: Tomdank@aol.com
Corvetteforum.com Member Alias: Strick

I made an adapter that allows the cooling system to be flushed using your garden hose. Here is what I did: drain the cooling system by taking out both knock sensors. Take one of the knock sensors to Lowes or Home Depot and buy two brass nipples, one end with the same pipe thread as the knock sensor and the other end with a barb end. Pickup some hose that fits over the barb end of the nipple, maybe 6 feet. Two more things to get, two garden hose adapters with one end barbed so that it fits into the 6 feet of hose, and the other end a female end that mates to your garden hose. Oh, Buy some hose clamps (4)and a "Y" for garden hoses. Now it's time to assemble. Cut the 6 foot hose in half. Insert the barbed end of the nipple into the hose and clamp with a hose clamp. Insert the garden hose adapter into the other end of that hose and clamp. Make two of these assemblies. Screw both of these assemblies into the knock sensor holes. Take the "Y" and connect both assemblies to your garden hose. This puts water into your cooling system, but you have to have a way to let the water out. I bought a Prestone flush kit many years ago and it had a yellow drain adapter that fits into the upper radiator surge tank with the cap off. I attached a washing machine drain hose to it and ran it to a big bucket. Now, you just turn on the water so that a nice slow flow comes out of the drain hose. When the water is clear, open the petcock on the bottom of the radiator. Again, run the water until clear. Close the petcock and crank up the engine while the water is still flowing nicely into the bucket. When it is clear, you're almost done. Shut off the engine and drain the system. Put the knock sensors back in IAW the manual. If you really want to be sure everything is clear, remove the two hoses going to and from the heater core and run some water through them. This takes less time than the drain, fill, run, cool down, drain, fill, run, cool down proceedure, and it does a better job.

 

I just flushed mine today; it was filthy. I did the throttle body bypass last winter and put one of those prestone flushing tees in the tube where the TB tee was. I also have an electric water pump. I put the garden hose on the tee and circulated the radiator water with the water pump while letting it drain. That was so easy, and no chance of messing up the engine because I don't have to run it with the electric pump. Bucket gets full, turn off the water; very little dripage.

I used Valvoline Professional flush because I knew it was really dirty. Flushed it for 30 minutes using the hose. Don't forget the overflow tank, it was full of crap. Then I used the new extended service yellow antifreeze. That stuff is supposed to mix with all other antifreeze fluids with no problems and protect the system better.

 

3.5 yrs. is too long to wait before you do a coolant change. Many people don't realize that not only does antifreeze raise the boilover protection and raise your car's ability to keep the coolant from freezing in cold temperatures, but there are additives that are placed into the coolant to prevent rust and metal fatigue.

It has been determined that after approximately two years, the additives are completely used up and are no longer present in the coolant. That's why it's advised to flush out your old coolant and fill her up with new. If you do not regularly change your coolant, your radiator and waterpump's lifespan will dramatically decrease. Metal in the engine will wear at a faster rate and everywhere that coolant flows, rust will begin to take a foothold.

If you take your car to a dealer or to a mechanic to have it flushed and filled, most places have machines that will automatically remove all the old coolant and will replace it with new. Those machines are pretty useful because if you do it yourself, you cannot remove as much coolant as those machines can because they work on vacuum. You simply cannot create vacuum with a garden hose.