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Bad head gasket, heads or wtf I don't know?

Reddekop

Reddekop

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Location
Canada
So I have a 94 yukon 6.5 td I just dropped and nv4500 in it real sweet truck. I bought the truck 3 years ago with blown head gaskets which I replaced with out issue. That was 60k km ago and now the truck started blowning smoke and eating coolant like it did when I bought it. So I got new (used off a truck with 98k km) heads and replaced gaskets glow plugs and injectors. Fired it up and it smokes worse then it did before the replacement began and now it's blowing coolant out the over flow. It's building so much pressure it blew the lower rad hose off. Any ideas where to look to find out if it's a block issue or head issue? Thanks in advance
 
Did you look for cracks between the valves on the heads that you put on the truck? Did you have the heads pressure tested? Welcome to the forum and it does sound like a nice ride.
 
Did you test the block?

At this point start out by removing fan belt, and thermostat crossover. Start the engine and see which side the bubbles are coming from. Now you can go from there.
 
I did not have them tested they looked brand new and the truck only had 98k on it so I assumed they would be ok.
 
The heads and the block are known to crack when overheated. 220 is top tekp you want to ever hit btw, and that is if you have the balanced flow waterpump. If you have the waterpump that uses a bolt on fanclutch, 220 for very long can crack the wall on a cylinder, most commonly #8, or the head - again usually #8 gets it the worst.
 
I upgraded to the 96+ ho water pump and dual t stat crossover right before the head swap. And since I swapped in the nv4500 and removed the tranny cooler my temp guage hasn't barely reached the half way mark even when hauling a trailer up mountain passes.
 
Yes, but you don't know how the PO treated the parts you bought. Like the guys said earlier the heads are very common to crack. I purchased a new set of loaded heads from Clearwater Cylinder many years ago, ran them for 50K miles with no issues on a plow truck.

It sounds like your loosing cylinder pressure badly to your cooling system. It needs a tear down and good check for cracks. Otherwise there may have been a mistake during re-assembly.

BTW, sounds like you got a neat rig there. I would love a 2-DR with an NV.
 
I'm planning a year down soon money is just tight right now. Ive learned my lesson. On buying used parts that's for sure. I really miss driving it I'm stuck driving my 97 6.5 that I swappped a nv4500 into as well so I still get to bring gears but the Yukon is way funner
 
IMO The lower hose blowing off is an install/clamp problem as the radiator cap tends to blow clean off before hoses under extreme pressure. Clearly you have other problems causing pressure.

You absolutely need to figure out what cyl bank, if not both, has the issue. @Will L. advice is bang on to figure this out. You may have a bad used head, cracked. Or you may have another issue, but, knowing what side to concentrate on helps. We take a chance every time we get used 6.x parts that they have cracked. This includes "used" for *your* block.

How did the block look as far as erosion on the fire rings of the head gasket area? Block deck warped? Assume you are not reusing single use TTY head bolts? Last thought is mucking up a head gasket on install.

Do not let your engine sit with this problem and "fix it months later" as coolant that made it to the oil will rust the valvetrain to ruin.
 
The block is true I checked that and I never reuse head bolts that's a no no and I wreaked the passenger side head gasket on My first installation attempt after the very rear bolt I stuck in the head to get it in snagged the gasket and tore it. I had to get a new one and the second time I got it no problems. It's been sitting for 3 weeks hence why I'm trying to figure things out before I tear into it. Also I don't have a garage and it just dumped a foot of snow last night so warmer clear weather is a must for me to continue
 
A five speed Yukon would be sweet to have. Good job on the swap over. A tear down would be the way to go. I would go back together with head studs if the block turns out ok.
 
Sounds like my '94 when the heads let go. Cracks between the intake and exhaust valves on 3, 4, 5, 6, & 8! Once one let go and it began to leak, then overheat, ka-blooey! I put 2 gallons of antifreeze mix, then another 6 gallons of water through it to limp it the 60 miles back home. On the highway where the cylinder pressure was high enough, no coolant/water loss. When I hit town and had to idle at a stoplight, I was dumping a gallon out the tailpipe per light!
 
Yea she eats coolant and pukes it at an alarming rate not quite as bad as yours by the sounds of it but have to add 2-3 gallons a day just to putt around town
 
War wagon is absolutely right about not letting it sit to long with the water in the cylinders. I let mine sit for for just 2 weeks and had minor surface rust in my cylinders. It would be more than surface rust if it sat much longer that.
 
There's no coolant left in the truck since it all dumped out the lower rad hose and I started it to move it from the street to my driveway yesterday and it didn't smoke at all which tells me she's bone dry of coolant
 
I have turns out it the drivers side I'm now waiting for some cash flow to have the heads checked
 
While you're waiting for the cash to buy a head(s), you might as well pull both heads and check them out. Forgot what year your rig is (need to put that kind of info in your signature), but if it's pre-97 you really should change out both heads, even if only one is bad, as the thermal shock will usually cause the other to fail shortly, too. Easier (and CHEAPER) to do both at once than to do each separately. Easy to tell visually, the cracks themselves between the valve seats are very noticable either naked eye of with a magnifying glass. Also, look for white streaks of burned coolant coming from between the valve seats.
 
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