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Discussion Starter · #1 ·
Just got a very clean 3.4 Convertible, put a new radiator, thermostat and flushed the heater core, car runs 180-200 but keeps pushing coolant out of the overflow, any tips for bleeding it? Really hoping its not a worst case scenario since the car is in great shape and has relatively low miles (100K).

Car worked good before I did the above items, but the coolant was horrible looking and heater was weak and was running a little cold, so did the above to rectify that and while the temps seem good (heater is OK) I cant seem to get all the air out of it, and doesnt appear to be any bleeders like on most vehicles (including the transverse 60 degrees which these are related to)
 

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'93 6-spd Trans Am - '96 C4
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I'd first test the coolant for traces of combustion just to be sure there's not a head gasket or potential cracked block issue. It's probably not likely, but it's a cheap test that confirms a lot... Other than that, if you do have a trapped air pocket, try jacking up the front end making the radiator the high point. That might allow the air pocket to move and clear.

I'm not familiar with the v6 engines offered in these cars. Looking very quickly into it, it sounds like some have the bleed screw and other don't. The procedure I read over said that "If you have an expansion tank the bleed screw is always open to it, so there is nothing to turn.". Confusing way to word it, but that's how it was written.

So... yeah. Try jacking up the front end and cracking open the radiator and overflow. Start engine, let it warm up, and raise RPM to around 1,200 for a minute or three once the thermostat opens to really push the coolant around. Other than that, if you still have issue, do that combustion test. AutoZone sells the test kit for under $30, and it is part of their free tool rental program, so a $30 100% refundable deposit is all you need to take it home. ...or you can buy it. Your call.



BTW: The radiator cap.... How old is it and what PSI is it rated to?
 

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Discussion Starter · #3 ·
I'd first test the coolant for traces of combustion just to be sure there's not a head gasket or potential cracked block issue. It's probably not likely, but it's a cheap test that confirms a lot... Other than that, if you do have a trapped air pocket, try jacking up the front end making the radiator the high point. That might allow the air pocket to move and clear.

I'm not familiar with the v6 engines offered in these cars. Looking very quickly into it, it sounds like some have the bleed screw and other don't. The procedure I read over said that "If you have an expansion tank the bleed screw is always open to it, so there is nothing to turn.". Confusing way to word it, but that's how it was written.

So... yeah. Try jacking up the front end and cracking open the radiator and overflow. Start engine, let it warm up, and raise RPM to around 1,200 for a minute or three once the thermostat opens to really push the coolant around. Other than that, if you still have issue, do that combustion test. AutoZone sells the test kit for under $30, and it is part of their free tool rental program, so a $30 100% refundable deposit is all you need to take it home. ...or you can buy it. Your call.



BTW: The radiator cap.... How old is it and what PSI is it rated to?
Brand new, 18psi Stant silver cap. Was bleeding it on a hill but will try to get it on ramps, very difficult with how long the front overhang is on these. will look into doing a combustion test, just really hope its not that lol Be good piece of mind if its not though, car runs great and does nothing odd other than the aformentioned stuff, guess there is a small chance there is a minor head gasket leak though and be good to rule it out.
 

· DELCO NERD
1993 Pontiac Firebird Trans Am, LT1 5.7L V8
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You could try filling the radiator to the top of the neck (you can even use water), leaving the cap off, and have someone crank the engine. If you are getting combustion gases in the radiator, you may see coolant squirt out of the radiator. It's not as reliable as an actual combustion leak (or "block") test, but if the leak is bad enough it will reveal it.
 

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Discussion Starter · #5 ·
Didnt get to do the test, but drove it around and seemed fine. Just swapped the radiator with an aluminum one since the prior new one had a crack in it from shipping that I hadnt seen, seems to be bleeding well and not noticing any aeration or anything other than the air bubbles and level drop when the thermostat opens while bleeding it.
 

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Discussion Starter · #6 ·
Did check it with a OBD 1.5 cable from red devil river and a laptop with the 94/95 L32 scan/test/data application and the ECM temp seems to stay around 191f-196f, trans temp was 210 to 215, gauge usually cycles from quarter to half which on the ECM indicates like 5 degrees so guessing the gauges arent super accurate?
 

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I do not know the details of the 3.4L V6, but I suspect the coolant temp sensor for the PCM is different than the coolant temp sensor for the gauge. Factory service manual (FSM) seems to indicate that. That means you have two different temp sensors in two different locations (the gauge sensor is usually in one of the heads). Hence, they can indicate different temperatures - 1) if the sensors or reference voltage are not accurate, 2) if there is air in the system.

The sensor reference voltage can be tested with a multi meter (typically 12 volts for the gauge sensor, 5 volts for the PCM sensor). Resistance vs. temperature can be tested with a multimeter, using ice water and boiling water. Here's the guide for the LT1 V8, applicable to 1995. The 3.4L V6 should be similar, just the locations would be different.


Check the factory service manual for the details of the location, and verify the temperature vs. resistance data. If you haven't downloaded (free) a 1995 manual yet, go here:

 
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