Overheating Cause Oil Leak?

[crdpoker]

Apologies, as I don't have the serial to the engine, but hope it's a general block question:

Can overheating a 5.0 cause oil to leak from the rear, near the distributor?

New-to-me-yesterday boat, 1998 Larson 226 LXI with 5.0gi engine. PO had said seawater impeller was changed 18 months ago - ran fine on muffs, water temp was 170 and steady, so I figured he was telling the truth. First dip into the lake, wife is waiting on me to park the trailer, and she calls me saying it's shut off and won't restart. Good samaritans help us tow it back in, temp is 230-ish according to gauge. Took apart seawater pump, and sure enough, impeller is old, crispy, and missing all the vanes. Buy new impeller today and change it in 20 minutes, removing the pump (so much better than what I'm used to, which is fighting Alpha One's), then pull thermostat housing and poke out all the black bits.

Lake test 2 today, and it's perfect. Pump is pumping (though too well, think thermostat is stuck open because it runs at 120 now) but new problem shows up - oil in bilge. Not a ton, but also not a small amount. Looks like it's from the drive shaft side at the rear near the bell housing. Can't tell where it's coming from, but judging by where it was and the fact that the distributor cap had drops of oil on it and the wires, I'm worried it's some sort of rear seal that melted or deformed from the overheat. Anyone have any advice? Not gonna sleep tonight,

Thanks,

Chris

 

[aerobat]

Re: Overheating Cause Oil Leak?

when you say its not a small amount of oil in the bilge first check the oil level in your engine - not that you run it for testing with critically low oil level .

maybe other can verify if a 5.0 GI has an overtemp auto shutdown or not , but when i understand you right you did not looked at the temp gauge and ran the engine until it died, correct ?

fill up engine oil and run the engine to locate where the oil is coming from. look closely at the head gaskets and manifold gaskets with a flashlight, and look if you get water into the engine oil.

but before you worry verify that its really "fresh" oil after the overheat and not old from lets say a previous oil filter change that you now first time see. do you have a very low or very high oil level when pulling the dipstick ?

 

[tpenfield]

Re: Overheating Cause Oil Leak?

I think there are 2 issues, one which you have solve (the water pump), the other may be more challenging.

Possibilities could be . . .

- Missing gasket for the distributor where it meets the intake manifold (causing oil spray)

- Crack in manifold or engine block that is allowing oil to leak out . . . could also be the head gasket as mentioned

Those 2 things come to mind . . . other may have some additional ideas.

Time to get out the flashlight and have a closer look.

 

[Scott Danforth]

Re: Overheating Cause Oil Leak?

your going to have to clean everything then look for the oil leak. yes, overheating can lead to an oil leak, either thru a compromised gasket, or thru a cracked block. Not saying that is the problem. it could also simply be increased blow by coming out the breather tubes when the motor was running hot.

 

[crdpoker]

Re: Overheating Cause Oil Leak?

Thanks everyone for the help so far. Will definitely start cleaning and looking - does anyone have any recs on what a good cleaning product to spray around the block to get the oil off but not damage anything? Simple green, engine brite?

-Aerobat - not a small amount, and did look lower on the dipstick than when I checked it in the driveway pre-launch. 99% sure it was new oil, level was low in the "add" region, but not non-existant. Not 100% sure on overtemp shutdown, wife was in the boat by herself, and since it ran perfect on the hose, I stupidly assumed it was fine. She was out for 10 mins or so at low speed idle, and reported that it shut off when trying to change from reverse to forward and then wouldn't restart. Will fill and look at head and manifold gaskets - am I correct in that if it's head gaskets I would get water in the oil as well (milkshaked) or could it just be oil going one way?

 

[Scott Danforth]

Re: Overheating Cause Oil Leak?

409.

hose everything down, let it sit, hose it down again, rinse.

 

[crdpoker]

Re: Overheating Cause Oil Leak?

Unfortunately not a great update - hit the engine with superclean, sprayed it down, and washed out bilge. Topped up the oil exactly to the line on the dipstick. Started it on muffs and ran fine in the driveway and with light revving, wasn't seeing anything, so decided to water test it. On the third 5 minute planing at 3000 RPM, engine surged and oil pressure indicated 0. Sure enough, bilge had oil in it, looked like it sprayed from the rear, again on distributor, intake valley, rear of throttle body, and dripping down bell housing (but still couldn't tell where it was coming from). Put an extra quart in it and idled back to the dock, now holding constant oil pressure at 40-45.

Checked dipstick several times - no overfill, no off-coloring from water intrusion, cooling system working fine and no overheat (good news). The only other thing that was strange was puffs of exhaust coming from an area around the oil pressure sender at the top right rear of the block (bad news). Sender itself didn't seem to be loos and the culprit of the spray. After higher rpms, there was also white smoke coming from the left hand valve cover around the oil fil vent (more bad news).

I'm worried based on the location of this strange smoke that it might be the notorious crack in the block in the lifter valley that Don S talks about. Will start breaking it down tonight, but would a crack in this area explain my oil spray (without water in the oil or overheating)? Would compression test tell me anything?

Thanks for the continued help,

Chris

 

[Don S]

Re: Overheating Cause Oil Leak?

Do you have an oil pressure sender near the distributor? It could be bad, the fitting could be bad. On the EFI engines, if the oil pressure drops to 0, it will bring down the rpm.
What is the full model number of your 5.0Gi ? There should be a string of letters following the Gi.
Year of the boat is not a good indication of the model year of the engine.

 

[crdpoker]

Re: Overheating Cause Oil Leak?

Video of smoke and oil spray from area I was referring to, behind and to the right of the air cleaner: 5.0 GI Problems - YouTube

 

[Don S]

Re: Overheating Cause Oil Leak?

You do have an oil pressure sender there.

 

[crdpoker]

Re: Overheating Cause Oil Leak?

Thanks Don - pretty sure it's a 5.0GI PBYCCE . If the fitting itself was bad, would that account for the puffs of exhaust seen in the video, or would it just be the oil spray? Will pull it tonight to be sure.

Thanks,

Chris

 

[aerobat]

Re: Overheating Cause Oil Leak?

i think you have "only" a shot intake manifold or intake manifold gasket, which is of course less nightmare than a shot headgasket or even a cracked block.

i helped a friend from our marina in replacing the intake manifold on a 5.7 mercruiser , he also had engine surging when giving power and even water in oil , but it turned out to be the manifold, no cracked block and no crack in heads.

be optimistic- i bet you have NOT a shot block.

 

[Don S]

Re: Overheating Cause Oil Leak?

i think you have "only" a shot intake manifold or intake manifold gasket, which is of course less nightmare than a shot headgasket or even a cracked block.

Intakes suck air in, not blow oil out.

If the fitting itself was bad, would that account for the puffs of exhaust seen in the video, or would it just be the oil spray?

Pull the sender and the fitting out of the block. Wipe everything down and put a 1/8" pipe plug (with some gasket sealer on the threads) in the oil passage and see if you still have the leak. (DO NOT use teflon tape)

 

[crdpoker]

Re: Overheating Cause Oil Leak?

Don - was trying to find a suitable 1/8 NPT plug, but couldn't at the big box store after work. Will go to a plumbing shop today. In the meantime, we uninstalled the sender and the fitting. Cleaned everything well, sealed it, and reinstalled. One problem was in order for the fitting and sender to be as tight as possible, they hit the accelerator cable bracket that is immediately to the right. Even with the bracket removed, this was the result: 5.0gi 2 - YouTube

Good news is it definitely looks like a source (hopefully THE source) of the oil leak. The only odd parts are the threads (both in the block and the fitting) looked great, no wear, no cracks, etc. We sealed it with Permatex The Right Stuff (in my experience, the gold standard of gasket sealant), which was recommended as sensor safe and fine for threaded connections - is this part of my problem, is there a better sealant choice for these high pressure oil connections? Do I need a different type of fitting/angle/extension to get this tight and clear that throttle cable bracket? Seems to only leak from the block to fitting connection, not the sender to fitting connection. Thanks for the continued help,

Chris

 

[crdpoker]

Re: Overheating Cause Oil Leak?

Don et al,

Pulled the pressure sender and fittings, and inserted a gasket-sealered plug as Don recommended. Once started, I could see the oil leaking from the area between the intake and the block (not the threads as I had originally suspected). Video here: 5.0 GI oil leak intake - YouTube

Can someone tell me whether this is something as simple as a blown intake manifold gasket (i.e. oil is supposed to be here and just leaking) or is it something more serious (cracked block, oil not supposed to be here)? Really appreciative of any help on this one.

Thanks,

Chris