Cooling System Air Bleed Valves for 1992-96 LT1

[Joe L.]

As part of the cooling system re-fill procedure for 1992-96 LT1's, the air bleed valves on the throttle body and waterpump have to be opened. Some coolant then can "shower" the engine which is not a good thing with an Opti-Spark distributor. It seems like some time ago I saw advertised some sort of gadget or tool which allows the bleed liquid to be captured. Does anyone have knowledge of such a device and source for it?

[Terry M.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

Joe,

Used to be a guy in Canada who sold the to us B-body guys, but that was way back.

Go to your FLAPS and get a brass radiator petcock -- 1/8 -inch pipe thread. Also get a couple off feet of clear plastic tube to fit on the end of the petcock. Instal the petcock in place of the bleeder screw (on the 1995 B-body we have no bleeder on the throttle body, and the coolant hose to the throttle body went by-by just before the AIR pump on my B-bodies. Even in Chicago I don't need heat to the throttle body, so you shouldn't either.) on the thermostat housing, put the plastic tube on the end of the petcock and the other end of the tube in the coolant resevoir and open the petcock. After a while the coolant coming from the petcock will have no bubbles in it and you are good to go.

[Duke W.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

What Terry says...

If you've ever done a coolant change on a mid-engine car, you know the drill. They can be very tough to bleed. My '91 MR2 has valves with hose nipples at the top of the radiator and at the heater core entry. Toyota even included the bleed hoses in the vehicle tool kit.

When the coolant is draining I open these valves, attach the hoses, then tie them to the front compartment cover support strut... fill with new anti-freeze/distilled water, SLOWLY, and bounce the car up and down during the process. Eventually the liquid in the bleed hoses should reach the level of the filler and at that point you know most of the air has bled out. At this point I close the valves, start the engine and run it at fast idle until the thermostat opens, top it off as required, then install the pressure cap. There is probably some residual air, as is typical for nearly all cooling systems, so over the next few heat cycles I check the recovery tank and add as required to maintain the proper level. After about the second or third cycle the level stabilizes, which means any remaining air has been purged.

Duke

[Bill H.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

I like Terry's idea of putting a hose on the T-stat bleed, may try it. But I've always just put a rag around the T-Stat housing and under the TB bleeder (92). i fill the surge tank with the bleeders open until coolant starts to come out, hand tighten, finish filling. Then run the engine until the T-Stat opens. I get 2-3 spits of air when opening the bleeders, then a solid stream, all caught by the rag. Not even enough to get the opti damp.
Watching the coolant in the surge tank, I can see bubbles coming up for a little while but that usually takes care of itself. Even after driving a bit, I don't get anymore out of the bleeders so i don't even bother with a second bleed anymore.
Just the way I do it but I've never had a problem with air left in the system.

[Joe L.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

I like Terry's idea of putting a hose on the T-stat bleed, may try it. But I've always just put a rag around the T-Stat housing and under the TB bleeder (92). i fill the surge tank with the bleeders open until coolant starts to come out, hand tighten, finish filling. Then run the engine until the T-Stat opens. I get 2-3 spits of air when opening the bleeders, then a solid stream, all caught by the rag. Not even enough to get the opti damp.
Watching the coolant in the surge tank, I can see bubbles coming up for a little while but that usually takes care of itself. Even after driving a bit, I don't get anymore out of the bleeders so i don't even bother with a second bleed anymore.
Just the way I do it but I've never had a problem with air left in the system.

Bill------


I've always used the "rag method", too, and pretty much have otherwise done the job as you have described..

[Bill H.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

Just a side note, I don't worry about getting a bit of water on my opti anymore, I put in an MSD with the nice o-ring seal on the cap and the billet construction that keeps the water out.
i had a chance to pull it off when I did the oilpan & timing cover gaskets. At 12k miles, it looked brand new inside.

[Joe L.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

Just a side note, I don't worry about getting a bit of water on my opti anymore, I put in an MSD with the nice o-ring seal on the cap and the billet construction that keeps the water out.
i had a chance to pull it off when I did the oilpan & timing cover gaskets. At 12k miles, it looked brand new inside.

Bill------

Yes, I like the MSD improved unit, too although I don't like the MSD cap in that it's "glaringly non-stock". Is the unit you are using on the '92 vacuum-extracted?

[Bill H.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

Bill------

Yes, I like the MSD improved unit, too although I don't like the MSD cap in that it's "glaringly non-stock". Is the unit you are using on the '92 vacuum-extracted?

Yea,Joe, thay all are. You have to pop in a fitting on the underside of the TB accordian for the air inlet. The vacuum line (with check valve), I teed in to a line under the right side injector cover, easy install.
The only slight pain for a 92 is that the MSD connector firs Caprice's and maybe 93 C4's, but not the 92. You have to hardwire it, no big deal.

I'm not wild about the red cap but the 92 is my daily driver (fair weather) and racetrack car. No plans to have it judged.

[Joe L.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

Yea,Joe, thay all are. You have to pop in a fitting on the underside of the TB accordian for the air inlet. The vacuum line (with check valve), I teed in to a line under the right side injector cover, easy install.
The only slight pain for a 92 is that the MSD connector firs Caprice's and maybe 93 C4's, but not the 92. You have to hardwire it, no big deal.

I'm not wild about the red cap but the 92 is my daily driver (fair weather) and racetrack car. No plans to have it judged.

Bill------

The vacuum extraction system is really critical to keeping moisture out of the distributor. Even if they got the cap sealed, there would still be plenty of opportunity for moisture to get in if the 92-94 venting system (holes in the bottom) was used. So, I'm not surprised that the 92-94 retrofit units are vacuum-extracted. Obviously, such a system is going to be non-stock and a negative from an originality perspective. However, functionality trumps originality in my mind, especially when it's very important functionality.

[Bill H.]

Re: Cooling System Air Bleed Valves for 1992-96 LT1

Bill------

The vacuum extraction system is really critical to keeping moisture out of the distributor. Even if they got the cap sealed, there would still be plenty of opportunity for moisture to get in if the 92-94 venting system (holes in the bottom) was used. So, I'm not surprised that the 92-94 retrofit units are vacuum-extracted. Obviously, such a system is going to be non-stock and a negative from an originality perspective. However, functionality trumps originality in my mind, especially when it's very important functionality.

I agree 100%. Here's what the inside of mine looked like after 12,000 miles and getting slightly sptitzed on 2 motor washes.