3400 Need ideas on Coolant System Problem

[rlchv70]

Need some ideas. Here are the symptoms:

Fluctuating Temperature, sometimes to red on coolant gage
Under Steady state driving conditions, temp goes up, then comes back down.
When temp is rising, the vents send out cold air.
When temp is falling, the vents send out hot air.
Sometimes, reving the engine will bring temp down.
Does not seem dependent on vehicle speed.
Hoses are firm, but not overly hard when warm.
Coolant level okay.
Replaced belt and water pump - hasn't pegged temp gage since, but all other symptoms remain.

Vehicle is an early 2004 Buick Rendezvous with 3400.

Any help is appreciated. My next step was to test/swap thermostat and pressure test system.

Thanks,
Randy

[Azrael]

My guess is the thermostat is having trouble switching between open and closed or not opening or closing fully. The hot air during a cooldown shows that the Tstat is finally letting coolant pass through the radiator and heatercore instead of bypassing it back into the engine block.

[SHOoff]

Vehicle is an early 2004 Buick Rendezvous with 3400.

Put my vote in for the Thermostat as well. Even though, theoretically, the new cars are supposed to pick that up ( at least I know they have a code for coolant temp lower than heat riser). Has it turned on the check engine light at all? Maybe swing by AutoZone and hook up a scanner to it and see if it pops up at all.

Generally, I try to go ahead and change the thermostat when I do a water pump. Just in case it happens to be bad too.

[KNTRDR]

How much mileage is on it? Depending on the mileage you may also want to look at the lower intake manifold gaskets, since all the 3.4's seem to suffer from this issue. I know mine acted a lil weird before the gaskets were finally replaced. You should be able to tell if you look around the #5 cylinder, and it slowly seeps out but you rarely if ever see any coolant puddles under the car because it lands on the transmission and evaporates. But a sure sign would be moisture buildup around that area and also possibly excessive moisture buildup inside the motor. That happened on mine as well. Foam on the oil cap, watery drips on the PCV.

[rlchv70]

Engine hasn't turned on the MIL light.

It has 42,000 miles on it. It is a 2004 model. I thought they had a good fix for the manifold gaskets? Also, it does not seem to be using any coolant.

Randy

[bszopi]

The 2004 should have the revised gaskets installed from the factory, so that shouldn't be a problem.

I'd change the thermostat and see what it does. If anything, you'll be out $5 or so and an hour or so of time even if it doesn't fix it. But I'd lean towards that as an issue as well.

[Rhedalert]

sounds like you have air in the cooling system. That would explain the fluctuating temperature and loss of heat. Now how the air got there is another question. It could be a bad intake gasket, but the simplest thing to do would be to bleed the system of air, make sure the coolant is topped off, and there's no leaks.

[rlchv70]

SES light came on yesterday. Code said it was a misfire in cylinder 1. Changing the t-stat today. I'll let you know if that helps.

Randy

[rlchv70]

Changed T-stat today. Went for a test drive. The temps fluctuated for about 2 miles then stabilized out. I'll see what it does over the next couple of days.

Randy

[rx191]

if you have a misfire on cyl 1 you have a leaky set of intake gaskets, they are leaking internally, are the lifters a little noisey if they are i would garrentee the gaskets are leaking, how long have let the motor run hot like that, because it also sounds like you mite have the start of a blow head gasket. if you over heated it to much you have caused damage

[rlchv70]

Engine got hot again today (haven't driven it much since Saturday). I'm going to do a pressure check on the system.

[rlchv70]

Alright, I pressure tested the system with mixed results.

When I removed the cap, the radiator was low. So, the question is do I have a leak or did I just not bleed the system properly? Can someone provide a proper bleeding procedure?

I pressurized the system, and did not observe any immediate pressure loss. It slowly dropped over time, but the results may be tainted because the car was slightly warm (pressure drops as the temperature falls).

I started the engine and the vehicle slowly built some pressure. I then completely pressurized the system. If there was a head gasket problem, the pressure should have increased rapidly and/or I should have felt pulsations in the gage. There was neither.

I'll repeat the over time measurement tomorrow with a stone cold engine.

Any other thoughts?

Thanks,
Randy

[Regal_GS_1989]

Cracked Head?? I had the same problem with my Regal, and the Heads were cracked across 4 cylinders. It didnt burn coolant, instead it would build up enough pressure to blow it out of the overflow tank.

[rlchv70]

I think I finally have it bled. I waited until it was hot and then opened the bleeder screws until water came out. At one point, i had to wait a few minutes because all of the pressure was gone.

Temperatures have been stable for the last couple of days, and dash heat is consistent.

I'll monitor coolant levels to see if it leaks over time.

Randy