Aopsahl7

Hey guys,

So I acquired my corvette about 2 years ago and so far have put about 3K miles on it. It runs great with a few little problems, but it is my never ending projec and I like it that way.

Anyways when I first got it I did not know much about cars but I have since gotten to know a lot. One of the things I did when I first got it was change all the fluids.

Question 1. - when I got it the vette had 127K on the clock and I stupidly changed the oil and put in synthetic. I now know that you generally should not put synthetic oil in a car that has run conventional it's whole 100+K life. I have run it with synthetic for 3k and there are no leaks. It looks like after about 3k of running it has burned about half a quart but no major leaks. With that said I was wondering if it would be better to change back to conventional high mileage or keep going with synthetic?

Question 2 - since I got the car I have battled with the cooling system. I flushed and flushed but could never get the coolant clean. Finally I gave in and replaced the hoses and the radiator. Flushed some more but I just checked and the coolant is a nasty brown with mud on the radiator cap. The engine cools fine and has no over heating problems but i know it just is not right. So with that said I was wondering if you guys had any additional suggestions on how to get it right. I think the previous owner put stop leak or some gum for some reason. Now it's my problem. Any suggestions? I have been flushing with a garden hose hooked to the flush fill tap.

94z07fx3

There is a tech tip that does a better job explaining but it is easy enough to make a hose that connects where the knock sensors go and attaches to a Y to your garden hose. Basically you take a knock sensor to home depot and match it to a pipe fitting with a barbed hose adapter on the other end then connect those to the Y via old garden hose or new vinyl hose and drain through the lower radiator hose disconnected from the radiator.

IMO a full synthetic in the proper weight is the correct oil regardless of OWT about them causing leaks.

A little bit of the stopleak isn't a problem. The factory put stopleak in C4s, for example.

superdave269

I have always been told once synthetic oil goes in that's what you have to use after that. Can someone explian why to me, not that I am doughting it but I never knew why.

Road Agent

Head gasket leaking?

jaa1992

Supposedly the synthetic is "slippier" than dino. What ever, I had no problems changing a 100K+ 88 to Mobil 1 after I changed a valve cover gasket. If you have no leaks and its only burning a qt ever 3000 miles keep using the synthetic and slowly increase your oil change interval.
5k should be close to optimal - have oil analysis done each change.

Do a search, blackstone labs has a kit where you send them a sample and they send you a report.

FYI my wife's 2004 with over 100k uses a qt every 3k - 4k. So you are in great shape.

Aopsahl7

Can you point me towards the tech article for flushing via the knock sensors? Also is there a tech for C4 vette section of the forum?

Head gaskets look like they are moist at the edges but no visible leakage. Guess I will stick with the synthetic oil!

Cliff Harris

It's possible that somebody put Dexcool (orange antifreeze) in your car. Don't EVER put that stuff in a car that has had the green antifreeze in it. It will take forever and multiple flushes to get the resulting mess out of your cooling system. Been there. Done that.

Shock96

Agreed on the Dexcool. It does the sludge thing when mixed.

Also, no problem with synthetics. Best choice IMHO.