Oil leak from dipstick tube

[frosh coach]

I developed an oil leak on one of my motors (2000 5.7 350 mpi mercruiser inboard). Due to the high pressure oil pump I shut it down when the oil pressure dropped to 38/40 psi while cruising so I didn’t damage the motor.

I believe it might be from one of the dipstick tubes as one is loose and the other is tight. On the none leaking motor both are tight.

Has anyone experienced this before? Anyone have a pic of how the tubes are connected to the oil pan?

 

[km1125]

A couple things...

First, 40 psi would not normally be considered "high" or "too high" at all for an oil pressure system on a normal ICE engine. You'd typically want a MINIMUM of 40 at high loads and RPMs, but it could go to 80 without concern. Why do you think that's high? Was that a typo and you really meant it dropped down to 40 and was lower than normal?

I'm not sure on that particular motor, but the two ways dipstick tubes are typically installed is that they are either press-fit into a hole in the block just above the oil pan, or they go into a 90 degree adapter at the bottom of the oil pan. When they go into that adapter, the ones I'm familiar with are flared so there's a flare nut to tighten to seal the joint.

 

[frosh coach]

A couple things...

First, 40 psi would not normally be considered "high" or "too high" at all for an oil pressure system on a normal ICE engine. You'd typically want a MINIMUM of 40 at high loads and RPMs, but it could go to 80 without concern. Why do you think that's high? Was that a typo and you really meant it dropped down to 40 and was lower than normal?

I'm not sure on that particular motor, but the two ways dipstick tubes are typically installed is that they are either press-fit into a hole in the block just above the oil pan, or they go into a 90 degree adapter at the bottom of the oil pan. When they go into that adapter, the ones I'm familiar with are flared so there's a flare nut to tighten to seal the joint.

Thank you for the info.
The engine normally runs around 50psi… I knew it had a slight leak. I was running back from block island to my home port in CT.

i noticed the pressure dropping down to less than 40, so I stopped to check and noticed a good amount of oil in the bilge.

my thought is these motors have high pressure oil pump which would def push the oil out of the bottom of the dipstick tube if that’s the source .

 

[techmitch]

Thank you for the info.
The engine normally runs around 50psi… I knew it had a slight leak. I was running back from block island to my home port in CT.

i noticed the pressure dropping down to less than 40, so I stopped to check and noticed a good amount of oil in the bilge.

my thought is these motors have high pressure oil pump which would def push the oil out of the bottom of the dipstick tube if that’s the source .

The oil in the pan is not under pressure from the oil pump.

 

[scoflaw]

That's not where the pressure is, it's a gravity drain back to the oil pan. If the pan isn't overfilled clean the area and put some rtv sealer around the tube where it meets the pan

Mitch beat me to it

 

[km1125]

If your tube goes down below the level of the oil before it connects to the pan (or pan fitting), then when the oil gets hot it will definitely leak out more than when the engine is cold. As others have said, the oil pump pressure has nothing to do with that kind of leak.

It should be obvious if that's where the oil was leaking out. If not, you still should fix the loose dipstick tube, but keep a close eye out for another leak somewhere else.

 

[frosh coach]

Plan is to finish clean up the bilge, put down the pigs (white oil blanket) refill engine with oil. A friend has a GoPro that you can watch live via Bluetooth. He wants to put under the engine and then fire it up to see if we can see leak.

 

[techmitch]

Good plan, save and post some pics.

 

[km1125]

Yea, keep us updated! And pics or movies would be great too!!

Just remember... you got REALLY LUCKY noticing that slight drop in pressure. What that really meant was you were ingesting air into the oil pump and compressing it too. The oil pressure doesn't drop as the oil level in the pan drops, it drops because the pump is starting to suck air.

Run it at the dock for a bit and see if you can find the leak. If not, then run it under load so that oil is nice a hot -FOR JUST A FEW MINUTES and then check again to see if you can find the leak. Anytime you're in the engine compartment then you should check the level too so you KNOW you have enough in the pan.

Did you already resolve the loose dipstick tube? What did you do?

 

[NorCalRobert]

Not sure if your boat motor has a PCV valve but if it does and it id]s not operating properly it will cause high crankcase pressure which can push oil out the dipstick tube.
I had a car years ago that the PCV valve was not working right and when I jumped on the go pedal the dipstick shot up so fast it dented my hood.

 

[frosh coach]

Yea, keep us updated! And pics or movies would be great too!!

Just remember... you got REALLY LUCKY noticing that slight drop in pressure. What that really meant was you were ingesting air into the oil pump and compressing it too. The oil pressure doesn't drop as the oil level in the pan drops, it drops because the pump is starting to suck air.

Run it at the dock for a bit and see if you can find the leak. If not, then run it under load so that oil is nice a hot -FOR JUST A FEW MINUTES and then check again to see if you can find the leak. Anytime you're in the engine compartment then you should check the level too so you KNOW you have enough in the pan.

Did you already resolve the loose dipstick tube? What did you do?

I will update this weekend when i can dive into it.

I did follow the dipstick tube to the pan/block. There wasn't much oil there on the pan. Not ruling that out but I don't think that's the culprit.

If I had to take a gamble, its the oil pan. The camera should tell.

side note, the motor was going to be pulled this fall anyways to replace the leaking (slow drip) dripless seal. I have v-drives so trying to get in there with the motor in wasn't happening. I'm thinking there was a chance that the salt water spray may have been getting on the pan when under way.

 

[frosh coach]

update - Pulled the motor out as I assumed it was the oil pan. Plus the dripless shaft seal on the side was leaking as well. Figured might as well as take care of two problems.

Well the pan was fine as well as the dip stick and banjo connector. The culprit... the last owner must have had the valve covers off for a repair... the cover and the gasket didn't seal correctly. The valve cover was actually dimpled allowing one side to leak. I was able to see this once the manifold was removed. All fixed any running great!