86TpiTransAm

I've had my '91 for about a year now and it has a very interesting problem that I'm trying to figure out but I'm lost. Ok, to start out ever since I've had the car, it's had a small antifreeze leak although I can't figure out where it's coming from. Last winter I had to put a little antifreeze in it about once every 2 or 3 weeks. Then through the entire summer I didn't have to put antifreeze in it even 1 time....odd! Now that the weather is getting cold again it's starting to lose antifreeze again somewhere. Ok that problem is mind boggling but here's the biggest thing that's stumping me right now. This has happened twice so far this year and several times last winter. When I drive the car for the first time of a day, the coolant heats up like normal but then continues to get hotter just like you get when you have a stuck thermostat. My original thought last year was a stuck thermostat so I replaced it with a delco and still had the problem so I'm fairly certain it's not the thermostat. The temp continues to rise to about 250-260 or so and the really weird thing is that when this happens, I get COLD air out the vents even with the heater on. The temp stays up for about 10 seconds and then slowly cools back down to 220 and then slowly back to 190-195 normal operating temperature and then my hot air is back again. After this happens once, it doesn't seem to happen again unless the car has set for 8 hours or more like when I'm at work. One shop I talked to suggested that it's getting an air pocket in the coolant somehow possibly from a leak (the leak I mentioned earlier that I can't locate). They say possible head gasket leak but they haven't looked at it yet and I'm doubting it.

My initial thought is that the air pocket (if that's what it is) is occurring in one of the hoses going to the heater core which would explain the cold air when this happens. If that's the case I'm wondering if the vacuum controlled heater/coolant valve on the passenger side of the engine could be where this is occurring... but how?

Does anyone know when/how this valve functions? Does it only operate when the heater control in the car is turned to the heater setting or does it happen at other settings as well? Can this be bypassed? The valve was leaking last year so it's new now but I will gladly get rid of it if there's a way to bypass it and still get heat.

The last time that this problem happened, the control was in the heater position. This morning I used the defrost setting the entire 10-15 minute trip to work and the problem didn't occur. After work, on the way to class, it was in the off position the whole 15 minute trip to class and the problem didn't occur. Coincidence? I'm planning to test this theory by not using the heater setting for a couple weeks to see if this happens again.

I'm really stumped with this problem so any advice/suggestions would be greatly appreciated. If I left out some need to know info, just ask. I've diagnosed as much of the simple stuff as I can. As far as the antifreeze leak goes there is 1. NO sign of antifreeze in the oil, 2. NO sign of oil in the antifreeze, and 3. NO exhaust "smoke/steam" indicating antifreeze going out the exhaust. I don't think it's a head gasket, or at least that's what I'm telling myself right now. It has to be something else and my gut is telling me it has something to do with the vacuum heater/coolant valve under the hood.

Thanks in advance to anyone who took the time to read all of this and has any input.

KrisW

iTrader: (5)

My 90 bird did nearly the same thing. I had two problems.

The heater valve on the passenger side was giving me problems. It was also leaking from a fitting under the throttle body. It never made it to the ground. It hit up near the water pump and then just dried there. When I pulled the intake I found it.

You might try looking at the water pump area.

86TpiTransAm

Thanks! I do know that I'm having a leak from the metal line below the throttle body which started last year after I broke the quick-disconnect and had to get a new one. I don't think I had that leak prior to that though so I'm not sure if that's the only problem. Plus I can't figure out why it didn't lose antifreeze throughout the entire summer.

I do think that heater valve needs to go but I'm not sure how to go about bypassing it. Has anyone ever done this bypass and are there any adverse effects to doing it?

Al Hasse

It can be bypassed, though I haven't done it, nor looked into how. By deleting, it allows coolant to flow through the heater core at all times, rather than only when heat is selected.

2_point8_boy

The Instant cold air from the heater means that there is definitly an air pocket. That combined with the fact that you say you are losing coolant and having to add some shows a definite problem. CHeck everywhere that coolant flows. All your hose connections, cehck around both heads and pay special attention to the intake gaskets. The GM 60* blocks have a major problem with leaking intake coolant passages. I do an average of 5 each month at my shop.

Water pump weep hole and front seal are also places to check.

I seriously doubt a problem with the heater control valve. Even if ti were shutting off flow to the heater core for a few seconds, you would still have heat because of the water temp inside the core when flow stopped. It would still be in the low 100's easialy.

Also, don't forget to check the radiator itself for leaks around the tank seems and the filler neck. The radiator cap can also be the source of phantom coolant loss.

Go over everything with a fine tooth comb and you'll find your problem, it's not just disappearing into thin air.

UK Speedbird

Has anyone mentioned the dreaded freeze plugs? I've had the same problem 86Tpi. No leaks in summer a nice little puddle at the end of winter. Could never work out where the leak was until i got under the car and had a good look at the block. I'm currently pulling my engine over winter to change the damn things (steel) for Doorman brass ones. I've herd that the 660's are prone to this.

Speed.