Losing coolant

[chessy56]

'01 DMax, LB7 w/400,600 miles
Head gaskets replaced ~62K miles earlier. Water pump replaced ~200K miles.
Coolant was a bit low, so about a 1/2 pint (give/take) was added. Engine was left to run ~1/2 hour in 0 degree temps. Within that 1/2 hour, the coolant developed too much pressure and was pouring out of the coolant bottle. Added about 1.5 gallons, ran the vehicle and had to add a little more several times. I'm currently consuming a bit of coolant with every 30 mile (+/-) trip on the highway. I've watched the coolant temp gauge in the cab go from ~180 degrees to 160 and back in the course of a couple of miles (air temperature from the heater dropped and rose accordingly). I see nothing dripping on the ground as of late; yet, level seems to drop with mileage.

Took this in to the dealership- they report nothing found. State it could be an air pocket that may be developing in the head (suggesting a questionable head gasket???). Topped off the coolant and ran a 50+ mile round trip and watched the temp gauge vary from about 170 to 210 and back within a 5 minute window of time. Looking for tips- thermostats going bad (they haven't been changed in quite some time)? Water pump? Head gasket failure after only 62K miles? The dip stick shows no foaming and the oil appears golden (not "orange"- not to say there isn't any getting there). No smoke from the tail pipe (except the normal smoke you'd expect under acceleration at 0 degrees air temp and lower).

Any input would help.

[CoyleJR]

The first thing I would try is to replace the coolant pressure cap. For years my 2006 LBZ would not stay full of coolant until I replaced the pressure cap. Since I replaced the cap three years ago it has not lost another drop of coolant. It is an inexpensive item that is often overlooked by mechanics.

One of Jim's old DP articles addresses the pressure cap issue and that is what lead me to change my cap.

Good luck
John

[Kennedy]

The fact that it rapidly built pressure and puked tells me head gasket. Did you stud it?

[rapidoxidationman]

What did the dealer do and look at to tell you "nothing found"? What does a pressure test show?

I've had a water pump impeller spin itself loose from its drive shaft on an intermittent basis that caused the problems you loosely describe: spiking water temps, hot/cold temps from the heater (cuz coolant wasn't being pushed through the core like it should've been. A new water pump solved it, but not before I replaced the passenger side head gasket thinking that was the problem.

[chessy56]

Heard from the dealership- don't know what tests were done, but they believe it is a blown head gasket. Pisses me off that I'll be dumping another $5K into this after only 62K miles. They believe exhaust (compression???) pressure is making its way into a coolant port. Don't know which side. JK: Don't believe they did a stud job- (if I understand your post, I believe they used new OEM head bolts- torqued to their yield point????).

Question now is whether they can replace the gaskets without doing any machining to the heads. Service tech states that they can only do one cut on these heads- otherwise, I'd be looking at another $3K for replacement heads. What are your thoughts? Is there a better head gasket than OEM? Any thoughts on just replacing the head gaskets without further head work?

I saw a post on these pages sometime back- coolant system was being pressurized by a bad head gasket- same result as what I'm seeing. Maybe time to retire the old girl to hunting/light hauling duty and get something different for everyday running. Still putting 600/week on it!

[More Power]

Chessy,
I'd wait till the suspect parts have been removed before making many plans. Have whoever does the work to carefully look at the head gaskets once the heads have been removed. You're looking for confirmation of the diagnosis.