I have had my 89 C4 about 2 years and I have brown dirt and grime floating in the antifreeze and collecting on the cap. When I first got the car the the antifreeze itself was completely brown. Not sure if it was the orange or green stuff but it was completely opaque. I drained and fushed as best as II could. I could not flush one side of the engine block because I could not get the Knock sensor off. Refilled with prestone yellow 50-50 and it loogs good, but it still gets brown globs in it and on the radiator cap.

The stuff looks kind of like oil, but when I take it out it has a consistency of slime-covered dirt.

I thought this might be a blown head gasket, but I have no symptoms of that. The compression is good and even on all 8 cylinders, there is no overheating, there is no water in the oil and no smell of exhaust gasses in the antifreeze.

Is it possible it is just residual stuff floating in the oil which did not get flushed because I could not remove the knock sensor? I also put in two "pills" as called for in the maintenance manual when I refilled it. Do these dissolve and create stuff in the oil?

There are no other engine or drivability problems to speak of, the car has 110k miles and aluminum heads.

 

Yes. There is a lot of coolant left in the engine if/when you don't remove the knock sensors. Heater core "stores" some too.

 

Rinse, repeat again and again, a bunch more

 

Let me guess you are using Dex Cool anti-freeze right?

I bought a Buick Terraza in 2005 and I had my coolant serviced like you were supposed to. It kept accumulating brownish sludge in the coolant and I too was wondering how this oily mush gets into the cooling system.

It turns out that Dex Cool does not like to go over 100,000 miles or ten years. My Dex Cool had changed it's PH and was damaging the head gaskets in my V6 engine. The engine overheated due to a head gasket failure and the head gasket had turned to a mushy substance itself in places. In the end (mine) the engine had to get both heads re-built to make the engine usable again. In my cooling system there was all kinds of gunk from the old anti-freeze and I had to flush it multiple times to get it clean again. The head gasket appeared to have disintegrated into a mushy grimy black substance

If my mechanic friend saw your Black stuff in your coolant he would tell you to expect a head gasket problem soon....

I wish Prestone still made their "Flush and Fill" kits! I still have one on my 1988 C4 and it is so handy to ensure all the crap is flushed out of the engine. I leave the hose running while I turn on the heat and try to help clear out the entire system with the engine running but not HOT. I flush the coolant out of all of my regular vehicles at 5 years and replace it with GREEN Anti-Freeze. But even this is not enough for today's newer cars. My daughter has a 2011 Camaro and it had it's heater core at 37,000 miles or so fail and start dumping coolant on the carpeting. A Chevrolet Dealer replaced it for close to $1800 but had to remove the windshield to do the job more easily. The new heater core is aluminum and very thin aluminum. A new Heater Core fail at 37,000 miles? Why is GM doing this to us? I know Copper cost more but it last longer than aluminum will. I am very disappointed in GM and Chevrolet for cutting cost in a place they should not be messing with. Copper is also heavier than the Aluminum and since they want Camaro's to go fast AND get mileage they are cutting back on weight.

I always use the Green Anti-Freeze and I mix it 70% Distilled Water 30% anti-freeze as where I live on the East Coast it does not get very cold. 70% water helps the coolant transfer more heat than a 50/50 system would. I might not do this in Wisconsin or Upstate New York but in Virginia it works great. Don't forget to replace the thermostat and your Radiator cap every ten years. Radiator caps loose their ability to hold pressure over time and this will potentially help the engine overheat. If the fins of your radiator are corroded up or just dirty try using some "Coil Cleaner" on the coils and you will remove all the corrosion down to the base aluminum. Coil Cleaner was designed for cleaning the coils on your Home AC compressor and it is safe to use on aluminum condensers and radiators.

 

You should do multiple flushes to get all of that brown crap out of the system. As mentioned, remove the knock sensors and take out the thermostat. Each time you put fresh water in the system, let the coolant temp get up to about 160, then let it cool a bit and then drain. Repeat 3-4 times.

Once the water comes out clean, replace the knock sensors and the thermostat. Refil with a good grade of ethylene glycol coolant in a 50-50 mix. Don't use DexCool in the pre-92 cars. Prestone works fine as will other brands. Do Not use the old GM cooling system pellets. Some years ago, GM issued a TSB that said to stop using that stuff. Seems it had a tendency to clog up the system. Keep checking the coolant for any signs of the brown color returning.

 

Thanks everyone. Not using Dexcool, I am using the Prestone yellow. Dexcool might have been what was in there before though.

I can't get the knock sensor out, maybe I could cut it off and use an easy out, but I don't want to start with that, because if I fail to get it out I will have to pull the engine to complete the job. It only has one knock sensor, the other side has an oil cooler bung.

Since it does not seem to be hurting anything, I am just going to live with it I guess.

 

You can leave that knock sensor in. Just drain as you did before. Fill with straight water, run the motor until it gets warm and the coolant has had a chance to circulate. Let cool and do it a couple more times. After the last time, full 50-50 with distilled water and Prestone. You should be fine for years.

 

2 years.


That's all standard coolant is good for.

WRT the 10+ year Dex Cool user....that is rated for 5/100k. Not 10 years. People need to do basic maintenance.

 

https://www.corvetteforum.com/forums...ush-works.html
Flush like this and you don't have to pull the knock's and you with flush out all the crap. Dan

 

Try this. https://evapo-rust.com/thermocure/

It worked a wonder on my 1970 SS Nova. It didn't matter how much flushing I did the coolant would be back to brown after a drive or two. Treated it once with the Thermocure and problem solved. It also improved cooling a bit which mattered a lot since these big blocks tended to run hot.

 

Your wish is granted

 

Hello auburn2,

When I bought my aftermarket knock sensor kit from MSD the gave you a knock sensor. The instructions were to find a threaded hole in your block and screw it in. In your situation I would simply put another knock sensor in a different location and wire it into the original knock sensor harness.

You don't have to kill your self getting the old one out when there are plenty of other mounting choices. Then someday when the block is out of the Corvette getting rebuilt they can deal with the bad knock sensor.

My knock sensor was overactive and hearing things that were not there. It pulled my timing back and kept it back since the knock sensor was triggering all the time. The difference was I could not spin the tires at all where as my neighbor's 1987 Convertible could spin them easily and frequently. A bad or non-functioning knock sensor will cause the timing to be pulled back about 10* and it is restored slowly. If the sensor is not working the engine will not let you damage it by retarding the ignition. You really do want to have a working knock sensor on your C4.

 

That's funny, i had the same issue with my car after changing to a warner knock sensor.
Started making my car gutless randomly.
I have an EBL, and logs showed it retarding timing.
Going off of times and my dash cam, i could see it retarding timing every time I hit a little bump in the road (84 Z51 aka go-cart package)...
My workaround was to limit how much it was able to retard timing, and limiting how long timing stays retarded...

I found my old knock sensor when cleaning the garage out a few days ago, it's going back in soon

 

quite possible the OP had some sort of stop leak such as “irontite” in his cooling system if this car was picked up used.

i had an 86 ironhead that a prior owner had treated like garbage and never fixed anytit was all bandaided. i drained, filled with 100% vinegar, yes thats what i did, let it sit for 2 hours, turned on the car to circulate, then drained. did multiple drain and fill cycles with hose water. then i mixed ip a mild baking soda and water mix. poured it in, let it sit for a couple hours. drained, hose filled, rinsed....then put in a 50/50 of prestone yellow.

ran SO COOL after that and it was stupid cheap and i let my vinegar and baking soda neutralizer fluids drain onto my lawn. so it was real easy.

just putting it out there.

 

Well I screwed it up. Tried to turn the KS with vice grips and snapped the top of it off the shaft. So now the threaded part is stuck in the block.

I can't get it out with an easy out and it is too tight in there for me to weld a nut head on to it. I might take it to the dealership to see if they can get it out with a stud remover. If not I will try to drill it out completely, it seems to be really soft metal (maybe brass?), so the sensor stud should drill out easy enough, but to to get to it I am going to have to drop the forward cats.... which likely means 6 more broken studs on the collectors, and they are not soft metal. It will take me all day and probably 10 drill bits to get those drilled out. If all else fails I guess I will pull the engine to remove it.

I feel like such a dumba$$! The car was running fine, it was cooling fine, I just didn't like the way the coolant looked so now I am in a world of crap because my coolant wasn't pretty. I should have left it the heck alone.

On the plus side I have 6 other cars so I can afford for it to be down until I can get to it.

 

It happens. Someone probably put it in too tight. I believe spec is 14 lbs.

Negative. If the hardware starts to give you trouble. HEAT IT. Use HEAT. Get a torch and HEAT the nuts until they are glowing red...they'll come right off. Use HEAT. HEAT works...every time.

 

Your coolant hoses may be breaking down internally. If original time time to change.

 

Ended up taking it the Chevy dealer here in Huntsville and asked them if they could remove the stub. The tech looked at and said "no problem 2.5 hours labor". So it cost me $350 but saved me an entire day on my back in the garage drilling it out. Great service too, I was a little hesitant to take it there being so old, figured they might turn their nose up at it but they were happy to help.

Now I have new KS installed, which I assume will come out easy in a few months. This summer I think I will change the heater core and flush again, doing both sides of the block this time.

As for the hoses, most of them are brand new. Not all if them but the heater hoses, upper and lower radiator hoses, and that litttle U hose are all new. The new hoses were in the box of parts I got with the car so I put them on when I flushed the first time.

 

2 years, drain the radiator and refill, keep that up and you shouldnt have any buildup of crud again.

 

Alabama? I take it that is the reason for your username.
If so, there's a place here called Corvettes Unlimited run by the folks that do Valley Vettes club.
Did you take it to the dealer on 72?