Mystery coolant loss

[gardnee01]

2004 Tahoe LT 5.3 85,000 miles.

I am losing coolant fairly quickly.

Recently changed thermostat because it was overshooting to about 230 degrees before it would open and cool down.

Mechanic did a pressure test and saw no problem. Oil appears uncontaminated. No fliud on garage floor at all.

Anyone offer suggestions on identifying the problem?

 

[91RS]

If you're losing coolant, it's going somewhere. I'd suggest going to the dealership, they know your truck better than anyone. I have a feeling it's probably the waterpump on that vehicle. Unless the coolant is just dumping, you're not going to see any coolant on the floor.

 

[matt14]

You have a coolant leak somewhere. you will have to pressure check cooling system. Does the car misfire, or blow white smoke when started. Make sure the there is not coolant on your floor. Maybe you have a leaking heater core. does it smell like coolant or sweet in your car? Just some things you may want to consider

 

[gardnee01]

Thanks

Thank you for your replies.

What would you expect for labor to replace the water pump? More than 2 hours?

Can I assume that it is not a head gasket if the oil remains in good condition? I have had to add more than a gallon in the last month. Oil changed 2 weeks ago.

Summary:
No loss when pressure tested 2 months ago.
No smell of anti-freeze in cabin, heat on or off.
No coolant on garage floor when parked overnight.
No smoke at start up
No misfire; runs great.
Oil does not appear contaminated.

A water pump does not scare me. A head gasket does. Aside from thermostat and oil changes, I dont work on this truck myself. I will have to rely on my check book.

I think I will have another pressure test. If this shows no pressure loss, should I just automaticly replace the water pump? Any other suggestions?

 

[91RS]

A water pump does pay 2 hours and the list price on a GM pump is $290. I would suggest going with the GM pump though. They come with a new thermostat and housing where the aftermarket ones do not and I have a sneaky suspicion that even the "new" pumps are rebuilt. Head gaskets are pretty rare on these engines if I'm not mistaken. Are you having to add a gallon EVERY month or did you just notice it was low recently and it took a gallon since it was probably leaking for a while? Sometimes the water pumps leak but it isn't from the weep hole so they leak slowly over time. Where do you usually get your work done? Since you going to pay to have this done anyway, I'd still recommend you take it to the dealer and tell them you had to add a gallon of coolant and give them any other info you have and get them to diagnose it so you know for sure what it is. That way you don't spend $500 on a water pump if that isn't what the problem is.

EDIT: Actually I just thought of something, but it isn't really good news. There is a problem with some heads manufactured by Castech and they can have a porosity crack in them which will cause coolant loss without any outward evidence of a leak. If that's the case, then you'll need a cylinder head or heads.

 

[gardnee01]

91RS

Thanks again.

Problem started about 4 months ago. First noticed when truck warned me of overheat. Temp got to about 250 degrees, but was taken care of right away. The coolant level was one gallon low. Added coolant, and initial overheat problem went away. Pressure test done at that time (no loss). Then noticed the thermo overshooting to 220-230 degrees before opening up, and was not producing cabin heat until it opened up. Changed thermo. No temp overshoot anymore. Since original warning it has been consuming about a gallon a month. Some months much less, but took a 1,500 mile trip in December that took a gallon (half gallon each way). So it started losing coolant sometime prior to original warning.

I did not mentione the first overheat because I did not think it got hot enough to do any damage. I know that is a good way to blow a head gasket. I just dont want to hear that is a possibility.

Routine work done by a local mechanic who is a good guy. He refers me to the dealer on things out of his expertise. This is the first maintance issue with the Tahoe. He suspected a cam/crank seal on my '98 Honda Civic causing a drop per week oil leak which was due for a timing belt anyhow. He refered me to a dealer on that and he was right. Timing belt/water pump/seal replacement took care of it.

Local guy did the pressure check on the Tahoe. I will take your advise and take it to the dealer for another pressure check/diagnosis/second opinion on the Tahoe and decide from there. I will post the result if you are curious.

Appreciate your advice.

 

[91RS]

Overheating it once probably didn't hurt anything. Yes, please do update with what ends up being the problem.

 

[mo0n]

Look at the water pump gaskets they are orange colored o-rings that seen to have a high rate of failure (all the new pumps come with black o-rings) Look up from under truck on drivers side and see if there is any coolant stains on block it will look like timing cover is leaking but no coolant is behind timing cover

 

[gardnee01]

91RS

[
EDIT: Actually I just thought of something, but it isn't really good news. There is a problem with some heads manufactured by Castech and they can have a porosity crack in them which will cause coolant loss without any outward evidence of a leak. If that's the case, then you'll need a cylinder head or heads.[/QUOTE]

Well, after 2 days at the dealership, they were stumped. I told the service manager about this Castec issue. He looked it up, removed the valve covers and it was caked with coolant soaked oil. So this is the problem. The extended warranty I purchased ran out 8 months ago of course. The dealership has indicated they will help me get this covered. On Monday they will be able to tell me what the resolution is. Will post later.

 

[Onatebuawer]

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