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.

[chessy56]

MP: presuming they do find that the head gasket is indeed bad.... This may be premature, but they'll probably want a quick answer from me as they won't want to tie up their bay for too long. What questions should I be asking, if any? What would you be concerned with?

Thanks for the quick reply!
Chessy (Gary)

[rapidoxidationman]

If they're dug in deep enough to replace the head gaskets, another half hour will get you a new water pump... It was a seriously sinking feeling to button up after replacing the passenger side head gasket only to have the engine get too hot on startup due to the pump impeller not impelling. Looking at the impeller with the lower radiator hose removed (used a scope) showed that it wasn't turning when a friend hit the starter.

Ask the dealer to check the water pump. Physically check it. BEFORE pulling the heads. They'll be draining the coolant first thing anyway.

[Kennedy]

The OE bolts in my opinion are the key contributing factor in the gasket failures. The heads just move too much and the fire ring collapses. Now the latest gaskets no longer have a fire ring which I also don't care for.

We use the latest version old style gaskets and studs. Skim cut the heads which should only take .002-3" to get them clean. A second cut is not that big a deal.

[chessy56]

John-
Thanks for the info on the Hd gaskets and OE bolts. I passed the information on to my service tech at Braeger Chevy (Milwaukee). Can't comment on what they've found so far as I haven't heard that they indeed confirmed the gasket failure. I'll post my findings/results as I learn of them. Appreciate the help.
Chessy (Gary)

[Kennedy]

When opened up the LB7 injector line corrosion issues will be revisited as well. They will not know anything about any other gasket besides the cheap 3 layer LML gasket.

[chessy56]

Head gasket failure confirmed- leak was spotted at the #7 cylinder. Tech states that the gasket had to be peeled off- didn't seem to have shifted (can't say it shifted when it was initially installed). They didn't seem to feel the issue was with the gasket, which leaves me wondering what the failure mode really was. There has to be one!

Inquired into putting studs in- it wouldn't have been a problem if they had somewhere to quickly order them from. In the interest of getting this thing back on the road, (and out of their bay), I told them to use what they had in stock (presumably, the OEM bolts; and most likely, OEM gaskets). It's at the point where I may relegate this truck to hunting/hauling and get something more fuel efficient for the 600 weekly mile commutes. At least they'll be in a position to quickly replace the pressure regulator on the pump- it has been surging and throwing codes on occasion.

I did put new injectors AND new pipes in about 16 months back. With luck, contamination from corrosion will be minimized. We'll see. All of my service work and mileage is logged.

If I keep this puppy for another few hundred thou miles and need another set of head gaskets, I might tackle the job myself. I'd be better off moving it along and looking for something a little newer.

[hoarder]

If you decide to have it repaired, make sure to use only oem kit specially the head gasket and also drain and flush the whole cooling system.

[Kennedy]

What you report is typical. Fire ring fails and collapses to the inside ie gasket no longer round. The #7 cylinder is also VERY common. They fail this way with BOLTS. I have never seen one repeat with studs including HP big boost applications.

[rapidoxidationman]

Is the number 7 cylinder the back passenger side?

If so, +1 to what Kennedy just said. That's the one that failed on mine a couple of years ago.

[More Power]

What you're looking for.... Leaks usually leave a track across a portion of the head gasket, or you may see some discoloration across the leak path if combustion pressure is finding its way into the cooling system.

If a head gasket leak is the primary suspect, I'd want some sort of validation for that diagnosis. Otherwise, the real cause could rear its ugly head after you've paid a lot of money for what may be unnecessary parts replacement.

Combustion gases can be measured in the cooling system using a special gas measuring tool that mechanics have access to. They just sniff the surge tank with the cap removed. Easy...

[chessy56]

So- the truck has got new head gaskets (again) and this time, I picked up studs and had the dealership install them with the rebuild. Also had them install a new pressure regulator as the engine had been surging a bit over the past couple of years and occasionally threw a code because of it.

Not seeing any leaks, and the reservoir bottle level seems to be stable. However, I'm accustomed to feeling some pressure on the upper radiator hose, especially after some 270 miles that has been put on it since picking it up yesterday. I can squeeze the hose w/o any pressure being felt even after the engine has come up to 180 deg. Kind of wondering about that. Any thoughts on the lack of residual pressure? (It used to always retain some amount of system pressure, even after sitting over night.)

[rapidoxidationman]

If a closed system like your engine cooling system starts with no pressure when it is cold, it should end with no pressure after cooling down after a heat cycle. Sounds to me like the mechanic did it right.

You were feeling residual pressure before the repair because the engine was adding volume (gasses) to the cooling system via a leaking head gasket.

[chessy56]

Oxidation: What you mention sounds reasonable, but I've noted pressure holding on the cooling system for years. In fact, I was surprised to feel this residual pressure long before my original head gaskets or sprays were replaced. I questioned it, even with the engine "cold", but was told that this is common for the Duramax. In this instance, I developed sufficient pressure to blow coolant out of the reservoir bottle. I never had this happen before.

I'll be taking another 250 mile highway run in a day or two. We'll see how it does and report my findings. Thanks.

[rapidoxidationman]

Just for kicks:
When the engine is cold (before you start it in the morning) open up the cooling system expansion tank cap to be positive that there is zero residual pressure. Run the truck for your 250 miles, or at least enough to get the engine up to normal operating temperature, and give the upper radiator hose a squeeze. Next morning, when the engine is cold again, give the hose another squeeze (should feel like zero pressure). Open up the tank cap again, and you shouldn't hear any pressure going in or coming out (assuming that the ambient air temperature is the same as it was when you previously opened the cap).

[chessy56]

OK- this thread is getting a bit long in the tooth, so hopefully it'll be on to better things soon.

Started by releasing the reservoir cap- "slight" amount of pressure release with the engine cold. Ran about 45 minutes averaging somewhere around 50-55 mph- stopped to check upper hose at filling station- warm, but relatively soft (little to no pressure). Ran the balance of the 250 mile run @ 60 (+/-) mph and checked the hose pressure after getting off of the freeway- warm and it had some pressure, but not "hard" like I was accustomed to in the past. Checked the upper hose after an overnight sit (cold engine)- soft, no stiff hose pressure as I had in the past. Released the reservoir cap: no pressure released at all. Noted that the coolant was a bit lower than when I started- maybe an air pocket finally moved out (no signs of coolant overflow however). This was running in 40 deg F air temp with a wind shield over the front grille. The Edge monitor I use reported coolant temps as high as 192 and as low as 183; averaged 186-188 across the trip.

I noted on the repair's bill of materials that both thermostats and the reservoir cap had been replaced in addition to the head gaskets ('stats' were replaced with an earlier tear down before). If this "zero pressure" state should be normal, I'd question if there was a redesign of the cap or if the original cap was partially at fault all along (I did notice that the new cap has no gasket- appears to be plastic on plastic seal; can't remember what the original cap looked like). Since 2001, the dealership replaced the injectors twice, I did the job myself once. The head gaskets were replaced once before and a coolant seal on the backside of the engine block required replacement last year as well. All of this work required a drain/re-fill of the coolant and in every case, I always had sufficient pressure to result in the upper rad hose being "very stiff"- regardless of whether the engine was hot or cold. And no lost coolant due to an over pressure condition! I'm baffled.

I spoke with my service writer- he'll talk with the repair tech next week. We'll let you know. Thanks to all for responding.
Gary

[rapidoxidationman]

Water under the bridge and all that, but it sounds like the first head gasket job was botched. It took a long time for it to degrade to the point that you needed to have it done again (properly this time, hopefully), but here's some anecdotal evidence for ya:

I bought my '05 used about 6 years ago. When I got it, every now and then I could get a slight scent of coolant. Had to add a cup or a quart every month or so. Drove it across the country, no problem. Eventually, it got to the point where the cooling system was belching fluid and I was adding a gallon a week. Hard hoses when it was warm, pressurized hoses when it was cold. That's when I took action and replaced the head gaskets, solving the problem.

Sounds like you've got the problem licked!

[DmaxMaverick]

The coolant pressure cap should have an O-ring, not a traditional gasket. It's located on the center part, just about mid-way, and under the threaded outer part. It also causes the friction you feel when installing/removing it. If it doesn't have this, or you don't feel the friction of the seal engaging the reservoir neck, it won't hold pressure at all, and may explain a few things.

[SoTxPollock]

My top radiator hose seems to be collapsing due to vacuum when coolant is cold, what does that suggest?

[DmaxMaverick]

My top radiator hose seems to be collapsing due to vacuum when coolant is cold, what does that suggest?

Time for a new pressure cap, and probably, new upper and lower hoses. Also check the turbo coolant connector hose behind/above the fan pulley, which is also likely in need of replacement (it's ~3" long). These are wear items, and with your time and mileage, are due.