'78 K10 Mystery Oil Leak

[RyanAK]

Brought the truck out of town for work the last two weeks for a little shake down... and because I'm bored to tears in the hotel after work and thought I'd do some small projects in the parking lot.

Rig is a '78 K10 Suburban Silverado with a GM Crate 350, TH350/NP203, 3.73 gears. Crate 350 was put in by a PO and only has ~4,000 miles on it.

Other than the vibrations I'm chasing at 45-55 and 65-70 mph, the truck is pretty darn comfortable and seems reliable.

I have an oil leak that's wetting down the starter pretty good... and since this is a GM crate 350 that supposedly has a place for a dip stick on both sides of the block, I suspect that the passenger side dip stick hole is open and the cause of the leak. The last spark plug gets a bit wet, and the rear of the exhaust manifold. But mostly its running down the back of the block, bell housing and starter. Oil and trans pans are slick. Ditto frame and front drive shaft. Ya think I'd be able to see the passenger-side hole to verify and make a plan to plug it. Nope. More effort needed.

I gently snugged down the valve cover since that was my first suspect. I'm fairly convinced it isn't leaking. No evidence around intake manifold or distributor either.

Anyone know precisely where the dip stick hole is on these and how best to get to it? I'm not losing much oil... maybe a pint in 700 miles... but it's a right mess that's definitely annoying.

Appreciate any guidance. Thanks, fellas!

Good grief. Old trucks.

[geezer#99]

Could be a common leak spot.
Like in the first pic in this thread.
Those two bolt holes by his knarly finger can leak if not plugged.
Easy to see to confirm.
You need a short bolt in them.

http://67-72chevytrucks.com/vboard/s...d.php?t=138417

[RyanAK]

That's a good thought... I'll have to run out and check. But all indications are that the leak is at the rear of the block. Thanks for the pointer, though. I'll report back.

R

[RyanAK]

Had to run an errand. Got back, popped hood, no bolts at the fuel pump. But... it looks dry. So...

First photo: missing bolts in front of block.

Second photo: passenger side. Notice the frame...

Third photo: passenger side rear where I think (thought...) the oil is coming from. I recently wiped off that spark plug.

[geezer#99]

Still might be valvecover gasket.
Clean it completely along the bottom where the gasket contacts the head.
Then check after running for any leaks.

[Dead Parrot]

If the valve cover gaskets are over 5 years old, they are my first suspect. Once they start going bad, tightening often just bends the covers, making the leak worse. There are some threads on a Felpro(IIRC) gasket that does a much better job then the generic cork gaskets. My 350 went from 1 qt every 700 miles or so to 1 every 2000 when I put in the better gaskets. This on a motor with about 100K on it. They can leak from the back two corners without showing much seepage other places.

There are some later/aftermarket pressure spreaders(not sure of the actual term) that are about 4 inches long instead of the inch or so of the OEM valve cover bolt spreaders.

Might also double check the PCV valve. If it isn't sucking properly, you could be getting some blow by pressure pushing out oil. Could be coming out around the bent pipe gasket in the passenger valve cover top.

[1976gmc20]

Might also double check the PCV valve. If it isn't sucking properly, you could be getting some blow by pressure pushing out oil. Could be coming out around the bent pipe gasket in the passenger valve cover top.

Top of the valve cover around the PCV valve looks dark/wet so I think that's your culprit

[cadillac_al]

I don't see no oil leak. GM went to black engines so we wouldn't see the oil leaks.

[RyanAK]

160 interstate miles home last night. Rear window has a pretty good oil film and the whole passenger side underneath is oily. There is a tiny bit of oil seeping at the PCV and breather on the valve covers, but nothing enough to undercoat the truck like this. Down 1/2 quart on trip home.

Today I got poking around to see if my suspicion about the missing plug in the dipstick gallery in the block could be the culprit. It’s almost impossible to get to on an assembled and installed engine. You just can’t see down between the exhaust manifold and the block.

So I crawled underneath, reached up behind the starter, and found the lump on the block casting. I could feel the hole, but couldn’t tell if there was a plug down in there. (These are supposed to be a cup something like a freeze plug...)

I ran in the house and got one of the kids’ bendy drinking straws and ran back outside and clambered back under the truck. Contorted myself again so I could reach the hole and bent the straw into a 7. Poked around with the long leg of the straw until it started in the hole and...

Yup. Straw became a dipstick. I had a wet tip. Went all the way to the sump in the pan.

This has to be the leak, no?

Now... from what I understand, the plugs are supposed to be tapped into the block with a punch and hammer. No way to do this with the exhaust manifold attached and the engine in the truck. Doesn’t matter anyway... none of the local parts stores know what the plug even is, let alone know how to source one. So Spencer and I bought a dipstick and tube that the kid at the counter thinks is the right one, and tomorrow we’ll see if we can fish it down to the hole in the block. Hopefully this solves the leak.

Fingers crossed!!

[1976gmc20]

Great! Now you will have the rare dual oil dipsticks option

[RyanAK]

Yeah... that didn’t work. Dipstick tube too big to fit in the hole. Ugh. Took 45 minutes to fiddle it in to find out it won’t fit. On to Plan C...

Any suggestions for Plan C?

[geezer#99]

If you don’t have it back togethor a pic would help.

[RyanAK]

First pic shows the drinking straw indicating the path between the block and exhaust manifold to the dipstick location.

Next couple are interwebs grabs of a GM crate 350 that show the passenger side dipstick location.

I cannot put eyes on this hole no matter how I contort myself. This is all by feel.

Just went to the hardware store and got a few 5/16” button-head bolts. That’s just a guess on size. Best plan now is to schmutz up a bolt that is about the right size with RTV, push it in, and hope for the best.

[geezer#99]

Wood dowel might work.
Easy to sand into a taper and tap it in.

[RyanAK]

Wood? Hmmm. I wouldn’t have thought about a lumberjack solution...

[RyanAK]

Any other thoughts before I go lay in the mud and give this a go? Will RTV give me a good seal against whatever pressure it will experience? Is a wood dowel a legit repair? I hate that I’m in this situation with an essentially new motor.

[1976gmc20]

Cork ????

[1976gmc20]

The new engine probably had some sort of temporary plug on both sides and now the one not used for the dipstick has fallen out.

[geezer#99]

Wood dowel with sealer or any other plug right now would be a temporary fix until you pull the manifold off to get better access.

[RyanAK]

5/16 body bolt liberally coated with RTV. Not a press fit, so I’ll be relying on the RTV to make the seal. Fingers crossed.

[RyanAK]

Told Dad what I was up to.

“So you’re deleting the rare continuous oil undercoat option?”

No respect. Ha.

[geezer#99]

Yup!
That’s called the ‘fogger’ option!
Best way to pay him back is park your leaker in his driveway and leave a big black spot!

[RyanAK]

I think the leaker is “fixed”. For now. Little shakedown ride seems to indicate the leak is stopped. I hate doing things half-assed. Driving out of town 160 miles for work tonight, so that will be proof of concept.

I can’t be the only sucker this has happened to... can I?

[RyanAK]

Apparent success!! Undercarriage is oil-free. Thanks for the encouragement along the way. Temp fix until it blows out or I have reason to pull the exhaust manifold.

[cadillac_al]

So some blocks have 2 dipstick holes??? That doesn't make sense.