Blown Head Gasket repair cost?

[scott2093]

Simple diag lead them to head gasket when they pressure tested it

You mean a leak down test? What is a pressure test? And why would both heads need to be done apart from I guess it's the right thing to do since it over heated..... I'm just asking but, shouldn't they be able to tell you if the other head gasket is good or not? Or even tell you which cylinder the bad one is leaking at?
Jeez...what if they get into it and the head/s aren't good?

 

[evilunclegrimace]

IF, I remember correctly GM book time is under 9 hours to R&R heads, that includes extra time for rusted fasteners. I was just quoted $320.00 for a three-angle vale job. Resurface the heads will most likely be time and materials. Ballpark for resurfacing $200-300. So, it all depends on the shops labor rate.

 

[Scooterwrench]

Nah it’s my to and from work daily driver, our farm trucks are all diesels. I guess you’re right though. Not much else to choose from shop wise and when you’re the only game in town it comes at a premium. I may just park it and see how my late fall season schedule goes if I want to save some coin

When you get it home drain the water and pull the plugs and shoot some WD-40 in each cylinder. Put the plugs back in and pull the coil wire out of the dist. cap and ground it then crank the engine over for a couple seconds to coat the insides of the cylinders and keep them from rusting until you can get the time to pull the heads. If water was getting in there those cylinders will rust up pretty quickly and WD-40 displaces water.

 

[NickTransmissions]

You mean a leak down test? What is a pressure test?

Coolant system pressure testing tools consist an air pump and gauge that screws onto the radiator. You pump it up to pressurize the system to a certain psi to see if it retains pressure or loses it within a short period of time (if it doesnt retain pressure, indicates a leak in the coolant syst. A block test is then conducted to see if the leak is at the head gasket(s). it screws onto the radiator in place of the pressure tester. The engine is then fired up and idled. a liquid solution in the block test tube changes color if hydrocarbons are present in the coolant system.

If the heads are cracked (one or both) just go get another one or two. Magnafluxing or pressure testing will reveal cracks.

Cylinder head gaskets should always be replaced in pairs, if i have a blown head gasket on bank 1, im pulling bank 2'as well since it's only another 10 min or so worth of work.

 

[Grandpa_truck]

Thanks for all the replies guys, I don’t really feel comfortable with the shops diag and quote so I’m just going to lay it up for a few weeks and do it myself. I can’t see spending 3k for a gasket replacement when I can buy a crate motor a few years down the road for 3k when this motor is really on its last leg. Still struggling with how the truck runs great most days and only twice overheated if it is in fact a head gasket.

 

[Scooterwrench]

You can check for cylinder leak yourself just by watching for bubbles coming up into the radiator neck or how quickly it builds pressure in the cooling system. Top it off with water and leave the cap off while it's running. If you see bubbles continuously coming up into the neck you have a leak. Put the cap on and squeeze the top hose. If it swells fairly quickly you have a leak.
If it passes those tests,no bubbles,no pressure build up pull the radiator and flush it best you can and pull the thermostat to see how well it flows water and replace it with a good quality T-stat and see how it acts.

 

[Grandpa_truck]

You can check for cylinder leak yourself just by watching for bubbles coming up into the radiator neck or how quickly it builds pressure in the cooling system. Top it off with water and leave the cap off while it's running. If you see bubbles continuously coming up into the neck you have a leak. Put the cap on and squeeze the top hose. If it swells fairly quickly you have a leak.
If it passes those tests,no bubbles,no pressure build up pull the radiator and flush it best you can and pull the thermostat to see how well it flows water and replace it with a good quality T-stat and see how it acts.

Thanks scooter, tstat is 3 months old but I’ve got that merit badge already and seen a brand new one stick in the past, so I haven’t ruled that out. I’m going to pick up a block tester with the blue liquid and see if there’s any exhaust gasses in the coolant. I also suspect a bad fan clutch after the shop had told me that was one of the things they wanted to replace. Maybe someone could correct me if I’m wrong but a blown head gasket stays blown and I’d have the over heat issue regularly… this overheat issue popped up twice a week apart. Could be a small leak I guess? But I’ll start with the basics that require less of my attention and time before tearing into the top end in a few weeks when I have more time.

 

[Scooterwrench]

Thanks scooter, tstat is 3 months old but I’ve got that merit badge already and seen a brand new one stick in the past, so I haven’t ruled that out. I’m going to pick up a block tester with the blue liquid and see if there’s any exhaust gasses in the coolant. I also suspect a bad fan clutch after the shop had told me that was one of the things they wanted to replace. Maybe someone could correct me if I’m wrong but a blown head gasket stays blown and I’d have the over heat issue regularly… this overheat issue popped up twice a week apart. Could be a small leak I guess? But I’ll start with the basics that require less of my attention and time before tearing into the top end in a few weeks when I have more time.

That sounds like that T-stat. Did it over heat while you were going down the road or while idling? Overheating at idle could be that fan clutch.

 

[Grandpa_truck]

That sounds like that T-stat. Did it over heat while you were going down the road or while idling? Overheating at idle could be that fan clutch.

Fan clutch seems good to me, If I spin it by hand it’ll stop on its own within a second, which tells me it’s not locked in the “open” and free spinning. I’m picking up a block tester with the blue liquid this morning and going to be certain if I have a bad head gasket or not. Still not convinced I do, no white smoke, no bubbles in tank while running and the oil on dipstick and cap is perfectly clear… I suspect a bad tstat and the local shop I brought it to purposely up-sold the job so they dont have to work on an old truck and can stick to oil changes and easy money.

 

[Road Trip]

You mean a leak down test? What is a pressure test? And why would both heads need to be done apart from I guess it's the right thing to do since it over heated..... I'm just asking but, shouldn't they be able to tell you if the other head gasket is good or not? Or even tell you which cylinder the bad one is leaking at?
Jeez...what if they get into it and the head/s aren't good?

The leak down test is primarily focused on troubleshooting where our air pump is losing
it's combustion chamber and/or bore seal. On high mileage engines, was the Intake valve bent by
#1 son's money downshift floating the valves last Saturday night? Exhaust valve burnt from too
many hard charges up the mountain pass? Piston rings have lost their mojo due to barrel-shaped
bore wear making them cycle in & out with every stroke? Or were they subjected to a bad overheat
and have now lost their spring tension needed in order to push against the bore?

That's the primary focus. But when you are putting ~100 psi into the chamber, if you take Schurkey's
advice and also remove the radiator cap, IF you have a leak between the combustion chamber under test
and the cooling system, then you will see bubbles in the coolant and no doubt see some related percentage
of pressure loss on the leakdown tester. (Keep in mind that we're pressurizing from combustion chamber out
through the head gasket to the surrounding cooling system.)

****

As for the pressure test, on the car this is done by removing the radiator cap and installing some test gear
which allows us to pressurize the cooling system to it's normal running pressure (~12-15 psi for our stuff)
and then monitor to see if we lose pressure over time. A really right engine/cooling system will hold this
pressure rock steady overnight with no loss. A slow seep may take an hour to show. Note: A stone cold
motor may leak slowly, but seal at operational temps. (due to expansion giving us more clamping action.) It's
even possible for a cold engine to be leak-free, but lose coolant at temp. (Think crack spreading with temp.)

Just like anything else, gross errors are easier to troubleshoot than weeps/seeps. And you need to think
through what you are doing, for water is even stronger than the General's connecting rods. (!) In other
words, if you are troubleshooting a suspected head gasket failure and the mill is using a lot of coolant,
then you should pull all 8 plugs before the test -- this way, if you happen to push more than a combustion
chamber's worth of coolant into a bad cylinder, at least you won't cause a hydrostatic lock and bend spendy
parts. (Also, the failing cylinder will self-identify when the coolant comes squirting out of the spark plug hole.)

Normally I'm not an absolutist about anything on a vehicle as old as a GMT400, but in this case any coolant usage
has to be at the very least fully understood, with the mindset of fixing it asap. (Unless you never drive your
GMT400 any farther than you mind walking home. :0)

For what it's worth, I've attached a hobbyist-level pressure tester to put a pic to the pressure tester phrase.
Stant & OTC are the next step up for anyone doing this kind of troubleshooting for a living. The only problem
with them is that they ala carte the adapters, so it's gets pretty spendy in a hurry if you have a fleet of dissimilar
vehicles.

****

Last but not least, depending upon the specific head gasket failure we can observe differing symptoms:

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* Combustion pressure into water jacket = overpressurized cooling system + fails HC in coolant testing.
* Cooling system into combustion chamber = steam cleaned spark plug(s) & combustion chamber(s). Also white smoke out of exhaust.
* Cooling system into lifter valley = mousse for oil. (If engine hasn't been run, water may show first, followed by oil when draining the oil pan.)
* Crack in exhaust port = white smoke in exhaust but no signs of wrongness on the spark plugs. Engine may run fine, for error is post combustion chamber.
* Assembly error (no sealant on head bolts that thread into the block where they are exposed to the water jacket) = coolant metered into combustion chamber.

Note: One difference between a leak down test and a pressure test is that the leak down test is higher pressure, but
also only stresses one cylinder at a time. (Some people only leakdown test the weaker cylinders discovered during
the compression test, so while they may find a burnt exhaust valve they may also miss a coolant leakage issue
by short-cutting the test process.)

On the other hand, a cooling system pressure check tests all cylinders in parallel, albeit with only ~15 psi of pressure.
(And keeping in mind hot fail vs cold fail scenarios as discussed earlier.)

So there are advantages & disadvantages to each of the 3 tests we have in our mechanical troubleshooting arsenal.

****

Obviously if you read between the lines I've worked on a lot of tired engines for myself, friends & family members.
Back when I was learning the ropes I was changing plenty of head gaskets using the Ready, Fire, Aim methodology.
If I was lucky the head gasket swap would work and I was a hero.

But every so often the problem would return after all that time/money/effort spent, and I would subsequently go
from Hero to Zero. :-( And after hob-nobbing with the Elders, I was taught that the more I understood the
problem *before* I open up the engine the better for all involved.

Compression test > leakdown test > cooling system pressure test are all tools that help the DIY mechanic
tighten up the problem definition prior to major surgery in order to fix a coolant leak and/or persistent overheat
while spending only the necessary money to do so.

And also help you determine if the valves are healthy enough that all we need to do is a head gasket, or should we
really get a valve job done as well 'while we are there'. :0)

Hope this comes across as a sensical explanation.

May your overflow tank always return to the same exact spot overnight.

Cheers --