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Hey all. I've read a lot of threads on this topic, most of which don't end with a conclusive answer. I'm already pretty sure this is a bad head gasket but I wanted to get some input.

2011 LML, just hit 100k miles. 30hp tow tune, I don't beat on it. EGR is intact but unplugged.

I performed a coolant flush about 4K miles ago & replaced thermostats (not upside down). I've had to fill it up a few times since then, assuming I passed some air through. However, recently I have been getting "Low Coolant" on the DIC. I look and sure enough the level is way below the seam. After sitting all night the upper rad hose is firm, not tennis ball hard but not soft either. I open the cap, pressure rushes out and the coolant rises back to the MAX line on tank. I don't think I'm losing coolant, the levels return to the same once I let all this air out.

I had the system vac flushed in hopes there's just some air pockets stuck somewhere; no change. Combustion fluid test was negative, although now I understand that test isn't accurate for the Duramax. Anytime I drive the truck, coolant level goes down past the seam. Like excess pressure is pushing the level down. I can open the cap, hot or cold, and the level will rise to the max line.

No visible bubbles in surge tank. Replaced surge tank cap. Not puking coolant, no drips on the ground nothing. Truck runs great, has good heat.

So what's the deal with bad HGs on the LML trucks? Some say they aren't prone to failure and others say they have seen a bunch of bad LML head gaskets. Is this something trapped air would cause? Or a bad surge tank? Just want to rule out the small stuff before tearing into this thing "eatS
 

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This was what was happening on my truck and end result ... Head gaskets. Never overhead, ran 60 HP tune.
 

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coolant loss

I received that message a few times over several months and always kept filling..

Recently I was changing out my pitman and idler arm / assembly, and noticed a drop of coolant on the frame. After further investigating it turns out the block heater has a tiny leak :(

my 2012 has 117K on it so maybe the oring for the heater is toast, so now its on the list of things to work on!

Obviously not related to pressure building, I had to change the HG on my 12v Sierra myself, but at least its something to read this fine morning! Hopefully its not HG's, but it makes sense..
 

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I sprung a leak in the tube on top the engine going to the egr cooler. Rubbed against the tube next to it wrapped in foil.
 

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Did you refill it using the diesel supplement method when you did the flush?

If not, that may be how/when it got damaged. (if you believe the warnings in diesel supplement)

Since it sounds like the problem started after the flush, it seems likely.
 

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Discussion Starter #6
Did you refill it using the diesel supplement method when you did the flush?

If not, that may be how/when it got damaged. (if you believe the warnings in diesel supplement)

Since it sounds like the problem started after the flush, it seems likely.
I did to the best of my ability, although there may have been some residual air still trapped in the system. I had this thought too. Reading the drain and refill thread it seemed pretty straight forward, but now I am hearing the only way to flush an LML is with the vac method. Could have been a very expensive coolant flush...

I received two similar quotes today. Book time for LML head gasket is 47 hours and almost $4,300 in labor... not including parts. I know its a lot of work but that seems high to me. I'm mechanically inclined and have some experienced help so I'm thinking about doing it myself. I'm familiar with the LLY but have never worked on an LML before
 

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Don't know if this will help or not; my 02 had a small crack in bottom of surge tank, took forever to find, would hold pressure when tested but lose it overnight.

My 09 had the same symptoms, would hold pressure when tested but also lose pressure overnight. Didn't see visible leaks anywhere because they would drip

clear of both trucks, but both would lose coolant. The 09 turned out to be the water pump, would never leak when I was looking. Murphys Law......
 

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Just for your encouragement, if it turns out to be headgaskets, I bought a 04.5 last year with 219k miles with bad head gaskets. When I bought it, I didn’t even know where the fuel filter was, that’s how new to diesels I am. But I bought the duramax engine boom, like $25 dollars, and followed the torque specs and procedures and did the head gaskets myself. The pricey part was getting the heads checked and surfaced. I bought my supplies from Lincoln diesels and they were really great to work with and great quality for a decent price.
There’s the encouraging news. The discouraging news is that on my 04.5 I was dealing with coolant loss weirdness much like you are, and my head gaskets seems to be great now, but I just finished the job last week and I am having the same weird coolant fluctuations. I had two issues going on, and I took care of 1 of them.
My radiator fins were full of enough material to build two bird nests out of. So, I think I know the culprit for getting it hot, now my suspicion is that I should have put a radiator in it while I had it all apart.
In all, it costs me about $2000 in parts to do the headgaskets myself, not counting the $1200 to get my injectors cleaned and inspected and some rebuilt. So, I might have saved $3000 doing it myself. It took me more like 100 hours. I went slow and cleaned parts along the way.
 

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Discussion Starter #10
I've pulled the trigger on HG, gonna be tearing into it next weekend. Once I get the truck up to temp I can look at the coolant tank and see it bubbling through the overflow like a hookah... this is without even romping on it. I'll be sure to take lots of pics and report my progress. I'll be putting a cp3 in it while I'm there, one less thing to worry about!!
 

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Had a busy weekend turning wrenches. Just taking my time and doing it right. Had a couple hang ups but for the most part everything came off pretty well! Just finished pulling the head bolts, although a couple of the outside bolts wont come out... the washer seems pretty well seized to the head. Hopefully pulling the heads tomorrow after work.



Also bought the injector puller from Merchant in case of a stubborn injector; glad I did. All popped out pretty easily except for 3, and the puller worked great on those.



So far the hardest part of the job was getting these ridiculous quick connect fittings undone. They sit upright so all kinds of road gunk, water, salt can collect in the fitting. I tried for hours to get the fitting undone but it was seized so bad. Of course, being on the driver side there is NO room to work. I ended up cutting the hard line and am going to replace it with a rubber line up to the valve cover.



 

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Discussion Starter #12
This plug for the dosing valve came with my cp3 kit. But I can't for the life of me get it to push in all the way. It's the same length as the factory fitting, but it stops prematurely and won't allow me to lock the plastic connector. Has anyone else had this issue?

 
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