I have a 1996 Suburban K1500 with 250,000. Until my son ran it out of oil, it
was an incredibly solid reliable vehicle. Since then I've driven it across
country and back twice but it is running increasingly rough.
I think it has a burnt valve and a blown head gasket. Symptoms: Runs
rough especially wile accelerating but runs fine on interstate. Compression
is 210 in all cylinders except #6-165 and #5-40. A wet test on these two
cylinders is: 6-185 and 5-45. Engine oil looks normal, not milky but without
any visible leaks the radiator is losing 1.5 gallons every 200 miles or so.
1. does my diagnosis make sense?
2. where is the most economical place to purchase decent rebuilt heads?
3. My original heads are cast iron and I see aluminum heads for sale that say
the fit my suburban. Should I stick with the cast iron heads?
Burned or bent valve and bad head gasket would be my guesses. I would get a set of heads that are the same material as you have now. The only other thing to consider is this vehicle has 250,000 miles on it. Is it worth keeping? If so would a rebuilt engine make sense?
Cylinder #5 is not firing at all. With a 40-45 PSI compression reading its most likely a burned valve as Bob said. Since the oil is not milky and the two lower reading cylinders are not next to each other I'd say the head gaskets are good. Cylinder #6 is weaker than the others but still firing. Since the second wet compression test did increase the reading on #6 the rings sound worn. In my opinion this motor, both top and bottom end, is tired. If the truck is in otherwise good condition I'd recommend either a rebuilt long block engine or a good used engine. Swapping out the heads will buy you some time but as I said, the motor, as a whole, is tired. Don't replace the heads with aluminium ones either!! Aluminum and cast iron have different rates of expansion and contraction. This puts stress on the head gaskets and will make them more prone to failure. Definitely not the way to go! At least in my opinion. HTH. -Jim
Both these guys advise is sound and I agree that there is more than likely a burnt valve. I would like to point out also, putting on a set of reconditioned or new heads would only pull the oil up past the piston rings thus making the motor into an oil burner. A refurbished or different engine I believe is what you are looking at.
Using a gallon and a half of coolant with no external leak in 200 miles points to a head gasket issue.
These heads are prone to cracking fyi. Your probably on the right track. Unless there is a hole in the piston (unlikely), your wet compression test verifies it's a upper end problem. I would just run a set of stock heads, make sure they are for the vortec style manifold (96+)
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