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Discussion Starter #1
Hello everyone, new to the forum. I’ve had my truck for about 9 months. I’ve had no issues with it up until about a month ago. My low coolant light came on so I filled the reservoir up and burped the system. Ever since then I’ve been fighting the coolant. Sometimes my truck goes a few days of driving without “loosing” coolant. Other times it’s one drive. I’m at a loss. It’s not puddling up underneath my truck when it sits. The coolant doesn’t appear to be going into my oil or my oil into my coolant. When I start my truck after it’s cooled off, the temp comes up to about 145 then drops to like 80-90 then 5-10 minutes later it comes up to 190-200 then bounces from 180-195 as it should. I’ve just continued to try and burp it because I read that sometimes they can be a real PITA to burp. I’m really hoping it’s not HG’s. I’m getting a coolant cap today to see if that helps and I also read of a guy who had similar issues to mine whom discovered his rad had a small crack so tomorrow I will be taking it to my shop and putting a burp funnel on it and letting her run for a good while with the heat on to make sure I’ve got all the air out. Should I do a pressure test on it after I burp it? 15 psi for 30 minutes or should I do that before? I’m new to diesels but not mechanically illiterate so I’d like to know all the things I can do to help diagnose it. Thanks for all the help y’all can give me.


P.s. 06 lbz GMC Sierra 2500hd AWD. EGR block off plates, K&N CIA, 3” dp to 4” mbrp, edge insight CTS2. Just turned 120k, bought it with 110 this past February.
 

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Discussion Starter #2
Bump for some insight. Got a new coolant cap from Autozone. Gonna make a pressure testing cap out of the old one.
 

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Have you checked the weep hole underneath the water pump or any signs of your lower radiator hose being wet?
 

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Discussion Starter #4
I read about the weep hole but haven’t checked it yet. Nothing appears to be wet or leaking but I’ve yet to confirm the water pump
 

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My 04 never left a puddle but it was definitely noticeable after looking underneath.. wouldn't hurt to take a look
 

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Discussion Starter #6
Thank you, I will do that and report back with my findings.
 

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Yeah, 120k...'bout WP time.
 

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Replaced the water pump pretty much immediately after I bought my lly with about 130k on it.
 

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Discussion Starter #9
I drove my truck briefly yesterday morning and parked it. When I checked the upper rad hose it was not hard. I’m searching for the weep hole in the water pump but I can’t see anything that looks like a weep hole. Even looked at multiple videos and I don’t see it. Put the new cap on before I drove it and topped it off with coolant but it’s low again. Below half a tank. Any advice on finding this “weep” hole. I read that once the trucks up to temp it more than likely won’t leak
 

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Moved to LBZ
 

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There are several areas up top that can leak while underway, roll off and hit the ground, not leaving a puddle. You might need to do a pressure test to find it, but the WP is the 1st and easiest to check.

On the WP weep,
Follow your lower hose up to the pump. The weep hole is behind that neck, between the hose and the block.
You're looking for any moisture/residue in that area...like this;
 

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I had this problem with my 03 Silverado. Was losing 1/2 gallon of cooling a week. If your truck has Castech Heads there is a known problem with developing small cracks at the internal (under the valve cover) Head bolts. It forces the coolant into the valve cover where the coolant water evaporates out and the glycol goes into your oil which mixes and you cant tell when you change the oil. Someone posted that they had fixed their problem with Bars Leak Head gasket sealer. I tried it and it worked like a charm. My truck had 175,000 on it and I never lost any more coolant and sold it at 230,000 miles.
 

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OP's '06 LBZ, different.
 

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Discussion Starter #14
I don’t see anything leaking or dripping around the water pump. I put the burp funnel on and ran it for about 30-45 minutes. Warmed up to about 160 then dropped to 85 slowly. I reved the truck to 3k for about 15 seconds and let idle for about a minute before doing that again. Then the temp came up to 210 and leveled out at 180. It sucked the entire burp funnel dry so I filled the funnel up about a quarter of the way and left it idle for another 10 minutes occasionally Reving to 3k for a few seconds. Turned the heat on high and left idle for about 15 minutes until no bubbles came up through the funnel. Shut the truck off and plugged the funnel and removed it and put the cap on. Letting it cool down now to see what happens. No smoke out of the exhaust when reving, oil isn’t milky and coolant doesn’t appear to have any oil in it either. The weird thing to me was the coolant pushed back into the funnel filling it before overflowing it for a few minutes up until the tstats opened, that’s when it sucked it dry. I’ve never experienced this before, is it a duramax thing? Is it normal?
 

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Discussion Starter #15
After burping the system, it idled right around 185 for several minutes. With full coolant. I plugged the burp funnel and removed it and put the cap on. Left it sit for about an hour, started it back up and warmed it up to 180. Reved it up to hit 190 and make the stats open, coolant dropped about 25-40% and didn’t come back up. Removed the cap slowly and topped it off with coolant. Put the cap on and reved it up to make the stats open. It dropped but came back up after the stats opened and closed. Did it 2 more times, got the same effect. Drove home to get my gear around to head to work. Sat for maybe an hour, went out and started towards the northeastern part of my state, 25 miles into my trip the coolant temp dropped to 130 hungout for a minute and bounced back to 185 and the low coolant light was displayed yet again.... t stats were replaced no more than a month ago with Autozone duralast 180-185
 

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Discussion Starter #16
Sorry just read everyone’s post on this page... didn’t realize there was a second page Lolol my bad
 

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Let's find out where the coolant is exiting the system.
Wrap a rag around the overflow tube end on the surge tank. Let's see if it's coming out there or not.

You've mentioned about no oil in the exhaust, no coolant in the oil, no oil in the coolant....those are all tell-tale signs of a HG problem...with a gas engine.
With the head design on the Dmax, a HG failure doesn't follow any of that logic.

It fails at the cylinder fire ring and slowly pressurizes the coolant system, forcing coolant out the overflow tube.
This also shows as an erratic reading on the temp gauge; staying low (when it should be rising) with no heat inside, then rising quick to operating temp (heater inside kicks in on full hot)...following by a 'low coolant' warning along with a plummet in ECT.

When you pull over and check, you'll find the upper hose soft and the surge tank level empty.

Stock ECT gauge; it's not accurate, it reads higher than actual.
In your last post, you mentioned 180-190, 160 and 130....if you did reach normal operating temp with stock 180/185 t-stats, the gauge reading should've been 200+.

You mentioned new VatoZone T-stats a month back, why?
Was there a problem of too cool?
Or were you chasing the wild temp fluctuations and coolant loss?
Or did this start after the new T-stats?

Air in the system from a reoccurring leak can cause the weird ECT swings.
If you could reach OP temp and not have the 'low coolant' come up, shut the truck off and park it overnight, checking the upper hose the next morning after overnight cool down, you'd see a firm hose there (like a tennis ball) if it was a HG problem.

However, at the rate you're losing coolant, that tell-tale test might not work.

Let's start with that overflow tube, see if that's the exit point for the coolant, and work from there.
Did you adapt the tank cap yet, for the 15psi pressure test?
 

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Discussion Starter #18
Okay, I can do that after I’m off and report my findings. I’m starting to think it’s a hg problem especially after what you said above. I made a pressure test cap but didn’t use it since I thought I had it figured out. I have an edge insight CTS2 that I’m getting my ECT readings off of so I’ve noticed that the stock gauge reads higher already. Like I said in my original post, I’m new to diesels and I know they’re similar in some aspects but very different in others. That’s why I came here. I know it’s definitely pushing back to the surge tank since when I was trying to burp the system, it would pull the coolant in when I reved it up, then when I released the throttle it would push it out like there was excess in the system...
 

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With the block plate mod, did you also bypass the EGR cooler, or leave it as is?

Rare, but a leaking cooler can cause a pressure problem as a boost leak blowing past the EGR valve. Bypass hose would rule that out.


As time has passed, we've seen that GM continued to use the flawed LLY HG design in the early production '06 LBZ engines.
While the LBZ didn't have all of the other contributing problems as the LLY did (flawed inlet duct, smaller rad, different turbo, etc), even with the old design HGs, failure on them is not as likely as they were on the LLY engines.
Rare, but it happens.
 

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When you finish, check to see if your truck uses these coolant tabs. The GM part number is: 3634621. I know that many GM’s used these. Most people do not know they exist. I have seen many head gaskets changed that only need these tabs. My 6.5 would not hold water until I put these in. The heads were fine.
 
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