1999 3.4 V6 Overheating

99 Alero 3.4 152,000 miles


I bought the car in January and it overheated the day I bought it. I took it to a mechanic who showed me how to bleed the air from the cooling system. He showed me where coolant was leaking on the back of the engine near the thermostat. I searched the forum and figured that I needed to eventually change the LIM gasket.

In the beginning I only had to bleed the coolant once every 3 or 4 days, but 2 weeks ago the situation worsened. I began having to bleed the coolant a few times per day. I parked on an incline (my driveway) and opened the bleeder screw for 10 or 20 minutes and no fluid would come out and the air from the heater never warmed up.

I bought the felpro intake gasket kit MS98003T and paid a mechanic $260 to install it. I also put on a new pressure cap, thermostat, and water pump. I also went to the dealer and purchased a new coolant bleeder valve since I rounded off the old screw. The belts and hoses appear fine. I had the codes checked at Autozone and they told me I had a miss on plug #3. They reset the codes, but the SES light soon reappeared and I haven't had it checked again since.

Yesterday, I bled the system for 20 minutes and the heater air warmed up. The surge tank never emptied. There is a loud squeal constantly coming from the belt area. Could a bad pulley cause overheating?

When I close the bleeder screw and put the radiator cap on, I drive for a couple miles and the air from the heater turns cold and the car overheats.

Suggestions?

I had a miss on plug #3. They reset the codes, but the SES light soon reappeared and I haven't had it checked again since.

Yesterday, I bled the system for 20 minutes and the heater air warmed up. The surge tank never emptied. There is a loud squeal constantly coming from the belt area. Could a bad pulley cause overheating?

When I close the bleeder screw and put the radiator cap on, I drive for a couple miles and the air from the heater turns cold and the car overheats.

Suggestions?

It sure sounds like a head gasket to me. Pull the #3 plug and check it. There should not be coolant on it. The number 3 plug is on the right (rear) of the engine, so you may want to use an exhaust gas tester over the coolant reservoir.

A bad pulley wouldn't cause overheating.

99 Alero 3.4 152,000 miles


I bought the car in January and it overheated the day I bought it. I took it to a mechanic who showed me how to bleed the air from the cooling system. He showed me where coolant was leaking on the back of the engine near the thermostat. I searched the forum and figured that I needed to eventually change the LIM gasket.

In the beginning I only had to bleed the coolant once every 3 or 4 days, but 2 weeks ago the situation worsened. I began having to bleed the coolant a few times per day. I parked on an incline (my driveway) and opened the bleeder screw for 10 or 20 minutes and no fluid would come out and the air from the heater never warmed up.

I bought the felpro intake gasket kit MS98003T and paid a mechanic $260 to install it. I also put on a new pressure cap, thermostat, and water pump. I also went to the dealer and purchased a new coolant bleeder valve since I rounded off the old screw. The belts and hoses appear fine. I had the codes checked at Autozone and they told me I had a miss on plug #3. They reset the codes, but the SES light soon reappeared and I haven't had it checked again since.

Yesterday, I bled the system for 20 minutes and the heater air warmed up. The surge tank never emptied. There is a loud squeal constantly coming from the belt area. Could a bad pulley cause overheating?

When I close the bleeder screw and put the radiator cap on, I drive for a couple miles and the air from the heater turns cold and the car overheats.

Suggestions?

You shouldnt have to bleed the air out once its all cleared out. Just sounds like you havnt got all the air out yet.

You dont need to leave the bleeder open the entire time. You just open it, if coolant sprays out close it. Repeat several times, and make sure your heater is on high heat and a low fan speed.

IMOthese systems are not very good in design, and are prone to failure!
MY Se constantly blows out coolant when I run it realy hard, over 5k rpms for an extended period. And all gaskets are new on it. :screwy:

But it could be your head gaskets too. With those miles I would have changed the head gaskets while it was torn down for the LIM change.

Good Luck

As an update, I had the mechanic replace the head gaskets. He sent the heads to the machine shop to get them leveled, said they were a little warped. The mechanic also noticed a hole in my intake, that he didn't see previously when the intake gasket changed. He replaced it with an intake from a 3.1 at the junkyard.

It idles fine, but if you drive it for a while, it will boil over and overheat. The mechanic said the fans should come on before the temperature gauge reaches the half point. They fans don't so the mechanic said maybe the coolant temp sensor is still bad even though we replaced it already.

The mechanic suggested I unplug the pigtail on top of the engine that is wired to the coolant temp sensor. With this unplugged, the fans constantly run, and the car doesn't overheat. The problem with this option is since the car doesn't know what temperature the engine is, the fans run extremely hard and loud anytime the car is running. A second problem I noticed is that when this pigtail is unplugged, I can feel the transmission shifting gears. When the pigtail is plugged in, the transmission shifting is not noticeable.

I don't want to tear anything up. What else can I try to do about the overheating?

When does it overheat? If it overheats while moving over 10 MPH, I would guess thermostat. But, I think most mechanics replace the thermostat when doing the lower intake (I do, anyway).

There could be dex-cool sludge buildup in the radiator causing it to not cool enough.

When does it overheat? If it overheats while moving over 10 MPH, I would guess thermostat. But, I think most mechanics replace the thermostat when doing the lower intake (I do, anyway).

There could be dex-cool sludge buildup in the radiator causing it to not cool enough.
If the car sits still and runs, it can idle all day without overheating. If I drive it for 20 minutes or so the temperature starts creeping up.He changed the thermostat a couple times, and he flushed the radiator once. Maybe he needs to flush it again.

As an update, I had the mechanic replace the head gaskets. He sent the heads to the machine shop to get them leveled, said they were a little warped. The mechanic also noticed a hole in my intake, that he didn't see previously when the intake gasket changed. He replaced it with an intake from a 3.1 at the junkyard.

It idles fine, but if you drive it for a while, it will boil over and overheat. The mechanic said the fans should come on before the temperature gauge reaches the half point. They fans don't so the mechanic said maybe the coolant temp sensor is still bad even though we replaced it already.

The mechanic suggested I unplug the pigtail on top of the engine that is wired to the coolant temp sensor. With this unplugged, the fans constantly run, and the car doesn't overheat. The problem with this option is since the car doesn't know what temperature the engine is, the fans run extremely hard and loud anytime the car is running. A second problem I noticed is that when this pigtail is unplugged, I can feel the transmission shifting gears. When the pigtail is plugged in, the transmission shifting is not noticeable.

I don't want to tear anything up. What else can I try to do about the overheating?

The 3.1 intake could be causing some issues...
Your fans work as follows..
The PCM commands Low Speed Fans ON under the following conditions:

The engine coolant temperature exceeds approximately 106°C (223°F).
The A/C refrigerant pressure exceeds 1310 kPa (190 psi).
The vehicle is shut off when the engine coolant temperature is greater than 140°C (284°F) and system voltage is more than 12 volts. The fans will stay ON for approximately 3 minutes.

The PCM commands High Speed Fans on under the following conditions:

The engine coolant temperature reaches 110°C (230°F).
The A/C refrigerant pressure exceeds 1655 kPa (240 psi).
When certain DTCs set.

Your overheating could also be air trapped in the cooling system, or you could still have a blockage/clog somewhere.

Have you checked or replaced the relays for the cooling fans ?
Also Make sure thier contacts in the fuse box are clean and not filled with (green)corrosion.

With the temp sensor unplug your trans will shift funny/harder then normal, its probly throwing all kinds of trouble codes too.

Your RAD is probably got clogged fins. Similar problem with my 97 minivan. Pulled the RAD out and found it full of debris, blocking the fins. Looked like a used furnace filter. I'd also look at replacing the water pump. GM has a new design for the impeller which I think performs better.

If the car sits still and runs, it can idle all day without overheating. If I drive it for 20 minutes or so the temperature starts creeping up.He changed the thermostat a couple times, and he flushed the radiator once. Maybe he needs to flush it again.

See if he just ran water through it or used a chemical flush. BG makes a non-corrosive flush chemical that works great if it's just sludge buildup. If the coolant got low and formed that crusty pink stuff, you may need a new radiator. I personally wouldn't try a stronger chemical because they can be hard on aluminum, and you sure don't want to take out the heater core.