93z383

iTrader: (-1)

Posted a thread about this not too long ago, but now some new issues have surfaced

Car is a 97 z28 M6, 30th anniversary with about 175k miles - The car runs beautifully, runs like it's brand new. Looks like the previous owner replaced the radiator with an OEM unit, waterpump & housing, and a lot of other things not related to my issue though. I myself have gone through everything 3 times and made sure all the hoses were good and routed properly, put in a new 160 thermostat and also ran the car without one to eliminate that possibility, pulled the knock sensor and flushed all the coolant, and changed the oil twice now.

From what I can see there is no coolant mixing with the oil or vice versa, absolutely no smoke from the exhaust, no sludgy oil, no backfires or missing, no check engine codes, nothing is out of the norm... waterpump seems to be workign fine, not weeping, and fans kick on like they should as well.

Ever since I got it, the car has ran a bit hot when sitting still or when I'm not going fast enough for the air to cool it a lot, it gets about 3/4 up but never overheats and runs great. Just yesterday though, the car started missing at low RPMS, and threw a code for O2 sensor heater circuit bank 1 I believe it was. 10 minutes of driving after that, the temperature spiked and the car was overheating, with coolant gushing and bubbling out the top of the resevior.

After getting it home today, I put in some extra coolant just to see if it would help and took it for a drive, and it seemed fine, but like before where it was running 3/4 hot, but nice and cool on the freeway with the air cooling it. I put the extra coolant in just to see, but the dipstick read that it didn't need any really, but obviously it helped.

I have no idea where to go with this.. any help is appreciated. Still no smoke or oil/coolant mixing, and aside from the missing from the 02 code which could or could not be related, the car runs perfectly smooth and powerful.

HELP!

93z383

iTrader: (-1)

BTW how do you even definitively test for a bad head gasket on a LT1? The guys at the auto store had no tester for it and had no idea what to tell me to do. I can do the headgasket myself if need be, but never had to test for one or replace one on my own car so I just need to figure out if this is even my problem first.

WS Sick

Do you have any blown fuses? are your fans turning on at the right time?

93z383

iTrader: (-1)

Hmm I didn't think to check the fuses, could that contribute to the problem other than the fans?

The fans are definitely running when the car gets hot, I will have to check and see exactly where they turn on at though.

A bad head gasket just seems extremely unlikely given the condition of the car, how well it runs, and how well the previous owners took care of it. When I bought it just about a month ago it was 100% bone stock, not 1 mod done to it other than a load of brand new parts - water pump & housing, radiator, clutch, tons of other stuff even the rear end fluid was new when I popped the cover to put the 410's in.

Whatever it is, I can fix it myself and I'm not too worried about it.. it just sucks not knowing what to fix.

WS Sick

If it has a blown head gasket, unless it is between the top of the cylinder and the lifter vally, you should have a t least a small amount of coolant loss. You can pressure up the system with a tester that screws onto the radiator where the rad cap goes, pump it up to operating pressure and see if it holds the pressure. If you have no loss of pressure here look at your plugs , and look for one that appears steam cleaned. Though you may not see anything out the exhaust, even a little bit of coolant in the chamber will clean the carbon off of that cylinder. The next step would be a leak down test on each cylinder to find the culprit.

If the fans are coming on Your fuse for that should be fine, I do beleive the 93s are a one speed fan. On or OFF

SHDY 5.7

How do u know for sure the fans are coming on? What temp? What brand t-stat?

Do u smell coolant inside of the car? Run the fans on a manual switch,and see if that helps. Turn the heat on "Floor" and check for coolant smell and or visual coolant coming from the vents. Could be a heater core issue,and not a head gasket issue.

Check around the heads for visual leaks,dont base it on what ur oil looks like.

93z383

iTrader: (-1)

The car in question is a 97 like I said, not a 93.

How do I know the fans are coming on? You serious lol? They are uh.. well, on. You can hear them, see them, and I even went so far as to stick a piece of paper in there to make sure they were going.

Ok I'm going to head to the auto parts store and grab a radiator pressure kit, after watching some youtube vids and searching around I saw people reccomending a combustion leak tester, but can't find anywhere that rents them and I'm not buying one.

I'll report back after i check the radiator out with the pressure kit, and go from there. When you check the pressure do you do it with the car on or off?


You mentioned a heater core issue, can you elaborate a bit? Like I said a head gasket seems unlikely but I guess it's possible, what could be possible with the heater core?

PS the t-stat is a SLP 160 degree verified in working order because I pulled it from my 383 car. It's brand new. I also ran the car in question without a thermostat to eliminate the possibility of that and it did the same thing.

WS Sick

Yes car off.
The heater core is in the dash on the passengers side, they are known to corrode and leak or get plugged up.

The factory fans come on around 210 degrees and the second one at 230!!!

Since you have a 97 it has the 2 speed fans and 2 circuits for that.

JCSWS6

iTrader: (5)

With your mileage I would check the water pump drive and see if the splines are worn off. This would allow the waterpump to still turn but not as fast as it should, on the highway it would be fine but low speeds would be killer. This is a pretty common problem that is easy to miss. I ended up doing a ewp becauses the shaft splines were almost gone on mine.

You'll have to pull the waterpump to check, but if you already tried everything I'd put a beer on thats the problem.

SHDY 5.7

Sorry,I meant to say "what temp are they kicking on at". The heater core can be bad,and cause over heating,and coolant loss.

FAD2BLK93

Looks to me the previous owner threw a bunch of parts at it and had the same problem. Then they sold it to U. If u turn your ac on or defrost on while the car is running the fans should come on, u can check them that way. Do a fluid test on the resovior to see if exhaust gasses are present. U need to check live data to see what the temp guage is at, to see if it is accurate. Good luck

CBear

I had a similar issue and it turned out to be a couple of crossed coolant lines. The return feed for the throttle body was hooked up where the overflow tank should have been. So as soon as the system got hot and built pressure the coolant rushed into the overflow tank and what was left in the motor overheated quickly. After swapping the lines back i haven't had a problem since. The overflow line should be hooked in at the top of the radiator and the return from the throttle body just below that. May be a long shot but still worth checking.

stevo9389

aside from possibly mixing up the reservoir lines have you checked for any blockage in front of the radiator? leaves or bags caught in between or in front of the condenser?