95 3.4 dohc air in cooling system

[John G]

I bought 95 z 34 for my son. The car has 135,000 miles on it. Shortly after buying it the oil pump drive cover started leaking. I pulled apart and on the advice of a GM mechanic I went ahead and pulled intake and installed new
gasket and bolts while I was there. Car was fine for about 2 months then my son told me the heat was not working. I drove the car to work and the temp went high (3/4 on gauge) then came back down. No heat till it came down
from thermostat opening. I installed new thermostat and refilled coolant as I had with bleeders open to get air out just like when I did intake. The car was fine for a few days and then I had to bleed air out again. This is an ongoing
thing It seems as if I'm bleeding this car almost daily. I will get hot as it did before and no heat then the thermostat will open and it will get hot. The system will have air in it every time. I've heard sometimes they can become air locked but this I feel is beyond that. I would be greatful for some advise, thank you.

[SappySE107]

Check your compression. I had a leaking head gasket that would pressurize the cooling system and push coolant into the overflow, and out the overflow.

If you can have the car on a decline, it is easier to bleed it, or an incline to check it with the radiator. That is, if it really does have air in it. Usually I only have a problem if I pull the rear head.

[Fierobsessed]

The coolant must be going somewhere too... I highly reccomend changing the radiator cap, and check the connection between the radiator (just below the cap) and the reservoir, if that is disconnected or leaky, you will pull air in each time you shut the car off.

Most people don't know that the radiator cap regulates the amount of coolant that there is in the engine, and each hot/cold cycle, dumps some to the reservoir when it gets hot, then sucks it back in when the car cools off.

[John G]

The coolant goes up in res. but only about 1 to 2 inches above hot line.
Sometimes it gets pulled back in after running up to temp and then bleeding
air out. The next morning it will be alittle low (probably due to me bleeding till I get coolant) I top it off to cold and when car is started everything seems fine. Then after a while of running the coolant is back up over full hot and does not pull back into rad. it stays alittle above hot mark and there is air in the system. I will try new cap and check the hose. If it
continues I'll also check the compression. It does seem like it is sucking air in, if not from the hose or cap any other idea where?

[z34phoenix]

how is the idle on the car? is it smooth or pulsing like an intake/ Vav leak? also what temp thermostat did you install? a 180* stat might help open the system quicker for you. and these cars do run hot in traffic or when not moving so a cooler Tstat might help in general.

but yeah check the cap. first.

[John G]

I replaced cap and the hose and clamps going to coolant res. I believe the thermostat was a 195 deg. Just a standard t-stat. I checked compression and it is low on rear middle cyl. When the car is idling it seems to surge alittle at start but after warming up seems to be ok. I also noted what sounds like a slight knock in front of engine around timing belt area. I believe this is from the tensioners and pulleys in timing set up. Called guy I have do machine work for me on other engines and he said he has seen several of these with same problem I'm describing have head gaskets and a couple have had slight
cracks in heads. He advised me that if I pulled engine and took down to bare
engine (acc. off) he could pull engine apart and do all machine work and tank engine for $1600. This would include reassembly ready for me to put acc back on and put in car, and he would replace the tesioners and idlers along with belt. Thinking this is the way I may go due to two shops have quoted me over $2000 to do head gaskets and replace belt and tensioners. I do thank everyone for help, and also since I'm going to have engine out is there any I don't want to say cheap but kind of inexpensive mods that can be done for alittle more power? Thanks again.

[Juglenaut]

So when you had to work on the oil distributor ring plug deal what did you all remove to access the oil plug?
Air may be coming in right at the lower intake manifold gasket, maybe it is not alined right, maybe it is a bad gasket(s) right out of the box. May even have a air leak in the upper I can't remember if all the bolts are blind or not?? Maybe the lower intake water nipple is bad. Vapor can effect compression.

Did you drain the coolant all the way out?? If so your heat core may have air in it, also don't rule out the heater it may have a very small leak and sucks air in on cool down, check hard lines for leaks or rust.

I would look at every avenue before spending that much money, check the plugs in all cylinders what do they appear like? Check all tubes that are weak and/or bulging at the connections.

Sorry I must deliberate:

Theroy of Heat of vaporization, point of condensation, pressureized suppression of liquious elements both boiling and melting.
Anyway to the point, heated water in a mostly non-colloidal mixture where exposed to heat and vacuum will separate and vaporize into a premixed state, water and concentrated coolant. Since the manifold has vacuum any leak in the gasket leading in the runner path will create water vapor which in turn will be pulled into a camber that is close to normal boiling point of water at sea level 212F if consentrated enough along with injected fuel will spontanously condensate back to water on compression giving pulsations in testing, this happens on a colder engine the pulsation will be more pronounced since the camber is closer to normal condensation, when water vapor changes states the volume changes equal to its mass as liquid water, vapor takes up more volume and is only compressable in the gasous state to the point of condensation.

In other words to much water vapor right at the valve(S) will drop compression on a colder engine.

[z34phoenix]

wow... nicely put!

i feel like im back in college! getting the sudden craving for BEER! and the beach!

[Jogasz28]

I don't know if this is your problem, but I just went thru it.
After replacing intake gaskets and oil pump O-ring, I had a "no heat" car complaint from the wife. Then she came home saying it was making a gurgling sound. When I checked the coolant it was out of site low. When I added coolant I saw it leaking from the rear passenger side of the engine compartment. I FEARED that I had a coolant leak at the head. It turned out to be the heater outlet hose (metal section) had rotted where it runs from the passenger side rear to front (towards the water pump). This section of metal tubing was rusted badly and had a leak. It had leaked at the rear elbow, but had also rusted badly at each clamp location.
I just replaced the bad outlet heater tube section and got it back on the road.
When I talked to the dealer he said it is a common problem.
FWIW, check it.
jogasz28

[Jogasz28]

Another tip

I read this in a GM TSB procedure.
When you are bleeding, put a dime between where the throttle stop contacts the set screw (sorry for my description). This will keep the idle up so you get the coolant moving fast enough, when the thermostat opens and coolant is hot, to get the air out of the engine outlet (large tube) bleeder and the heater bleeder.
I just did it and it worked great.
BTW, DO NOT ADJUST THAT SET SCREW!
Good luck,

[SappySE107]

We used to have ambitions of putting the TSBs on this site.

[Jogasz28]

We used to have ambitions of putting the TSBs on this site.

I've got an alldata TSB account for my '95 Monte Carlo VIN X. I just haven't had time do anything with them (work has been insane lately, new software to learn). There's quite a few of them. Is there an easy way I could give them to you?

[bszopi]

Just zip them up and email them to me... bszopi@60degreev6.com

[Jogasz28]

Just zip them up and email them to me... bszopi@60degreev6.com

You've got mail.