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Do some searches on this site, there's tons of information on cooling system service.
Here's the shortest version:
Drain the radiator, heater core, engine block (remove knock sensors). Also drain any reservoir or expansion tanks in the system. Flush the entire system with fresh water several times. Drain completely. Reattach everything and refill with fresh coolant, using the proper mixture, dilute as necessary. Run engine to full temp, let it cool completely (this is called heat cycle), then burp the air with the bleeder. Some systems are self-purging of air, I'm not very familiar with the L98.
Took me about 2 hours to do a careful job on my LT1. It helps to have the car jacked up or otherwise lifted in the air for accessing knock sensors and catching all draining fluid from the various areas.
There are knock sensors in the block that prevent larger particles from getting out of the engines water passages. To do a thorough flush you should pull these sensors out. You need to put a special kind of grease on the knock sensor threads before you reinstall them. I don't know what kind of grease, maybe someone will chime in with the correct name and where you ca get it. You could buy new sensors that already have the grease on the threads, I hear they are inexpensive.
You should look through the cut out in the radiator shroud on the passenger side to see if you have any trash in your radiator and condenser. I have to pull my radiator because it has quite a bit of trash in the fins and I plan on flushing the cooling system at the same time.
There are knock sensors in the block that prevent larger particles from getting out of the engines water passages. To do a thorough flush you should pull these sensors out. You need to put a special kind of grease on the knock sensor threads before you reinstall them. I don't know what kind of grease, maybe someone will chime in with the correct name and where you ca get it. You could buy new sensors that already have the grease on the threads, I hear they are inexpensive.
Some say to use Teflon tape on the knock sensors to prevent leaks, but Teflon tape could prevent grounding of the sensors to the block, and you don't want that. Use just a little anti-seize compound (looks like grease lol) on the 3rd-5th threads of the knock sensors, don't overdo it. Anti-seize is commonly used on exhaust bolts and sometimes on spark plug threads. The most important thing about the knock sensors is to torque them properly, not much force is needed here, just enough to stop coolant leak from the hole. My LT1 was 14 lb-ft or something like that. In this case it's better to use less force than risk using too much... if they leak coolant, just tighten a little more. You should check for leaks after service anyway. And yes you can buy a new knock sensor, if the old one is not working. They are sensitive devices so handle them gently, but don't assume it doesn't work just because it's 28 years old.
Originally Posted by 94corvetteC4
You should look through the cut out in the radiator shroud on the passenger side to see if you have any trash in your radiator and condenser. I have to pull my radiator because it has quite a bit of trash in the fins and I plan on flushing the cooling system at the same time.
This is a very good idea. When you're done cleaning out any debris, you might want to install a couple layers of fine wire mesh (1/4-3/8 inch grid) on the air inlet below the front bumper to keep road debris out of the radiator and condenser. I bought a whole roll of galvanized wire mesh from Home Depot for $8 and this may be the best thing I've done to my car. It won't prevent everything from going in, but it will keep the big stuff out and that's what matters the most IMO.
I don't know what a knock sensor is but I will look it up.
Will definitely look for and clean out any debris around the radiator.
So I am gathering that its not necessary to fill with distilled water, run to full temp, cool and drain ? Most folks here seemed to not think so.
The knock sensor is part of the ignition system, it senses detonation (a.k.a. pre-ignition or "knock") in the cylinders and sends a signal to the computer, which retards the timing to prevent continued detonation and potential damage. This all happens instantly so you won't really know it, except you might hear occasional pinging for a brief moment. That's normal. When there is no detonation, the ignition system will advance timing as far as possible (at the very edge of spark knock) for best performance. The knock sensors help the system to keep the spark ignition right at the very edge, which is ideal.
The debris tends to collect between the radiator and AC condenser, and on the front surface of the radiator in general. Be sure you are looking in the right area.
You can flush the system with distilled water if you want to, it's only $1 a gallon but many people (including myself) don't bother. If you use concentrated coolant, you definitely want to use distilled water when diluting the mixture.
Enjoy your super clean car! And post a few pics for us!
Factory original except for one headlight cover repainted about 15 yrs ago. So 28 yrs.
It belonged to the father in law of the guy I bought it from. He bought it new and it was his toy. Weekend driven, garage kept and babied. Got a very good service history with it.
When he died it had 45000 miles. He left it to the guy I bough it from who put 3 k miles on it and treated it similarly.
Based on the service history, condition of the vehicle and the price, it was a once in a lifetime deal.
Of course my neighbor brought home a Blue 2016 stingray with 9k miles that day !
Just my $0.02 - but I've pulled the Knock Sensors out of more than one C4, and while it's not difficult - it does make a pretty big mess, and it just isn't a "fun" job (you can pretty much count on getting coolant all over you....)
If all you're trying to do is to get fresh coolant in - the drain the rad - refill with distilled water - drive it a bit - drain it again, and refill with straight coolant (not the pre-mixed coolant) is not that bad a plan. There is no question - you will get more "junk" out of the system by pulling the knock sensors than by just draining the radiator. Pulling the knock sensors is "the right" way to do the full coolant flush, but it will take significantly more time, and IF the cooling system has been properly maintained over the years, it probably isn't necessary to do. Getting new coolant with new "additive package" IS necessary every few years.
Knocks are a must or you leave a gallon of crap in there. I put in new fairly cheap and the right dope on them torque is important. I will not put back 20+ year old parts.
Last edited by antfarmer2; 04-29-2016 at 05:49 PM.
04-28-2016, 12:10 PM
Radiator Coolant Flush
Very nice! 
