1996 Lumina APV overheating - air pocket?
locator299
10-01-2005, 11:17 PM
I've seen other posts, but none of them seem to fit my problem...
I've got a 1996 Lumina APV minivan with a 3.4L V-6 engine with 96,000 miles - I've owned it for 8 years and drive very conservatively. The engine overheated while my son was driving it - he kept driving it while it was overheated and later said that there was a problem with the van because the "engine stalled" when he was parking it.
I easily reproduced the overheat just by letting the van idle on a hot day. I turned on the heater to try to suck out some of the heat and it pumped out tons of heat (the heater core was not clogged).
After the van cooled, I opened the drain cock on the radiator to drain out all of the Dexcool, replaced the 195 degree thermostat (what a pain!) and refilled with a 50/50 mixture of new DexCool. After I started the van the dash temp gauge still tried to peg high. I had forgotten all about bleeding the system! Both fans turned on, in sequence, as the temperature went up. I stuck a screwdriver against the water pump and put my ear against it - it sounded smooth (no grinding) and there was no water leak, so I believed that the water pump was working OK. I turned off the van and let it cool down.
I checked the DexCool coolant (nice orange color and no oil in it), oil (dark brown/black), no smoke from the exhaust and no smell of antifreeze in the air.
Still not realizing that I had not bled the system, I decided to replace the radiator. I drained out all of the coolant again. I installed new upper and lower radiator hoses, a brand new radiator and a new 50/50 DexCool/water mixture. I started the van, but again forgot about bleeding the system! After the van warmed up, the temp gage went up to about 2/3 scale (and the first cooling fan turned on) before I finally remembered to bleed the system. I used the bleeder valves on the thermostat gooseneck and at the water pump. The van was pointing uphill (about a 10 degree uphill street) while I was venting, but the temperature kept rising. The second fan came on (meaning that I was now overheating for sure), so I turned on the heater - but NO heat came out! (even though I had LOTS of heat before I had originally drained out all of the coolant). Again, I had to turn off the van to let it cool off.
I've added coolant, bled the system, driven the van up and down steep streets and revved the engine RPMs over a two-week period - to try and get all of the air pockets out. The overflow tank does have lots of coolant in it.
I think that I've noticed a trend with the temperature gauge readings. The gauge wants to red-line when the van is being driven on flat and down-hill streets. However, the temperature will stay one white line below red-line if going up a slightly steep hill. If I have to rev the engine harder to go up a steeper hill, the temperature will again start rising towards red-line. However, if I idle the van on a slightly uphill street, the temperature will slowly come down to mid-scale and the last cooling fan will turn off. Other than not driving the van, nothing seems to consistently get the temperature to stay at its normal mid-scale reading (like it did before the overheating problem started).
I've heard that it is tough to get all of the air out of the 3.4L engines. Could there be an air bubble that I'm just not getting (remember the heater that worked before I drained the coolant - and now doesn't work!) Would a vacuum pump help to remove any remaining air? Or is there something else I've overlooked? Would a blown (head or intake) gasket show any of these symptoms?
Any help would be appreciated!
I've got a 1996 Lumina APV minivan with a 3.4L V-6 engine with 96,000 miles - I've owned it for 8 years and drive very conservatively. The engine overheated while my son was driving it - he kept driving it while it was overheated and later said that there was a problem with the van because the "engine stalled" when he was parking it.
I easily reproduced the overheat just by letting the van idle on a hot day. I turned on the heater to try to suck out some of the heat and it pumped out tons of heat (the heater core was not clogged).
After the van cooled, I opened the drain cock on the radiator to drain out all of the Dexcool, replaced the 195 degree thermostat (what a pain!) and refilled with a 50/50 mixture of new DexCool. After I started the van the dash temp gauge still tried to peg high. I had forgotten all about bleeding the system! Both fans turned on, in sequence, as the temperature went up. I stuck a screwdriver against the water pump and put my ear against it - it sounded smooth (no grinding) and there was no water leak, so I believed that the water pump was working OK. I turned off the van and let it cool down.
I checked the DexCool coolant (nice orange color and no oil in it), oil (dark brown/black), no smoke from the exhaust and no smell of antifreeze in the air.
Still not realizing that I had not bled the system, I decided to replace the radiator. I drained out all of the coolant again. I installed new upper and lower radiator hoses, a brand new radiator and a new 50/50 DexCool/water mixture. I started the van, but again forgot about bleeding the system! After the van warmed up, the temp gage went up to about 2/3 scale (and the first cooling fan turned on) before I finally remembered to bleed the system. I used the bleeder valves on the thermostat gooseneck and at the water pump. The van was pointing uphill (about a 10 degree uphill street) while I was venting, but the temperature kept rising. The second fan came on (meaning that I was now overheating for sure), so I turned on the heater - but NO heat came out! (even though I had LOTS of heat before I had originally drained out all of the coolant). Again, I had to turn off the van to let it cool off.
I've added coolant, bled the system, driven the van up and down steep streets and revved the engine RPMs over a two-week period - to try and get all of the air pockets out. The overflow tank does have lots of coolant in it.
I think that I've noticed a trend with the temperature gauge readings. The gauge wants to red-line when the van is being driven on flat and down-hill streets. However, the temperature will stay one white line below red-line if going up a slightly steep hill. If I have to rev the engine harder to go up a steeper hill, the temperature will again start rising towards red-line. However, if I idle the van on a slightly uphill street, the temperature will slowly come down to mid-scale and the last cooling fan will turn off. Other than not driving the van, nothing seems to consistently get the temperature to stay at its normal mid-scale reading (like it did before the overheating problem started).
I've heard that it is tough to get all of the air out of the 3.4L engines. Could there be an air bubble that I'm just not getting (remember the heater that worked before I drained the coolant - and now doesn't work!) Would a vacuum pump help to remove any remaining air? Or is there something else I've overlooked? Would a blown (head or intake) gasket show any of these symptoms?
Any help would be appreciated!
jeffcoslacker
10-02-2005, 06:04 AM
A blown head gasket will produce it's own air pocket and screw things up sometimes, but I suspect that you have somehow (by the angle of the vehicle most likely) trapped a huge amount of air in the heater core.
It may just be the sequence of how you are bleeding it also. Or a combination. Here's what I would do:
Find yourself a nice flat surface to work on.
Let the engine cool for several hours.
Open the radiator, open both bleeder screws.
Fill until coolant is rolling from both bleeders, close them first, then close the radiator.
Start the engine, with the heater on full (temp, no blower), and let it idle until the gauge reads normal temp.
Shut it off, let it sit about 10 minutes.
Carefully depressurize and remove the cap, open the bleeders.
Refill until coolant flows from both bleeders.
Close the bleeders, then the cap.
Start the motor again and let it come to full temp.
Keep repeating this until you can't purge any more air. sometimes it takes a few cycles if it has a lot trapped.
It may just be the sequence of how you are bleeding it also. Or a combination. Here's what I would do:
Find yourself a nice flat surface to work on.
Let the engine cool for several hours.
Open the radiator, open both bleeder screws.
Fill until coolant is rolling from both bleeders, close them first, then close the radiator.
Start the engine, with the heater on full (temp, no blower), and let it idle until the gauge reads normal temp.
Shut it off, let it sit about 10 minutes.
Carefully depressurize and remove the cap, open the bleeders.
Refill until coolant flows from both bleeders.
Close the bleeders, then the cap.
Start the motor again and let it come to full temp.
Keep repeating this until you can't purge any more air. sometimes it takes a few cycles if it has a lot trapped.
locator299
10-06-2005, 08:26 AM
Jeffcoslacker, I started following your procedure - but once the temperature started rising, it just kept rising towards the red-line, so I had to terminate the procedure and turn off the van.
Since I had to take a break to allow the van to cool off, I gave some more thought about my van's symptoms. I finally realized that my van's symptoms could also be due to having no flow through the system. (No heater output, cool lower radiator hose cool while the upper hose was super hot, temperature gauge rising almost non-stop).
Even though the water pump was making no noise and not leaking water from the weep hole, I took the plunge, bought a new water pump and tore off my old water pump.
THAT WAS THE PROBLEM! Instead of a cast metal impeller, the water pump had a black plastic impeller. It had cracked from the center bolt to the edge - on both, opposite sides of the impeller. So, the serpentine belt could spin the pulley (and turn the center impeller bolt), but the two halves of the impeller just moved apart when the pulley spun. The plastic didn't hit the spinning center bolt - so no noise!
After I put the new water pump on, the system bled flawlessly, the temperature gauge stopped at the mid-way position and the heater started pumping out lots of heat again.
MORAL OF THE STORY: Not all failures show the typical symptoms!
Even though the water pump was making no noises and the weep hole was not leaking coolant, I should not have just assumed that the water pump was functioning properly. If I would have paid more attention to the overall symptoms, I would have saved myself a lot of time and a little bit of cash.
Since I had to take a break to allow the van to cool off, I gave some more thought about my van's symptoms. I finally realized that my van's symptoms could also be due to having no flow through the system. (No heater output, cool lower radiator hose cool while the upper hose was super hot, temperature gauge rising almost non-stop).
Even though the water pump was making no noise and not leaking water from the weep hole, I took the plunge, bought a new water pump and tore off my old water pump.
THAT WAS THE PROBLEM! Instead of a cast metal impeller, the water pump had a black plastic impeller. It had cracked from the center bolt to the edge - on both, opposite sides of the impeller. So, the serpentine belt could spin the pulley (and turn the center impeller bolt), but the two halves of the impeller just moved apart when the pulley spun. The plastic didn't hit the spinning center bolt - so no noise!
After I put the new water pump on, the system bled flawlessly, the temperature gauge stopped at the mid-way position and the heater started pumping out lots of heat again.
MORAL OF THE STORY: Not all failures show the typical symptoms!
Even though the water pump was making no noises and the weep hole was not leaking coolant, I should not have just assumed that the water pump was functioning properly. If I would have paid more attention to the overall symptoms, I would have saved myself a lot of time and a little bit of cash.
richtazz
10-06-2005, 12:35 PM
That must have been a cheap aftermarket waterpump on your van, as I have never seen one with a plastic impeller.
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