Oil slick whilst engine running

I'd forgotten about this until I started to recently re-commision my '88 Sea Ray Seville 4.3L Alpha One.

I had replaced the elbows, exhausts, flappers (with the new style), upper stern drive seals, water pump impeller and housing etc. Upper housing seals, gimbal bearing, drive bellows, exhaust bellows, water hose, shift bellows.

However after a great outing last year we pulled back into harbour and at moorings there was a small oil slick whilst the engine was runiing.

I read an article from hear that said it could be from the trim pipes, which I am yet to investigate. However it was almost as if there was some oil coming out of the engine, which from my motor trade background seems odd. Unless there is some sort way in which a marine engine could displace oil via the exhaust.

It could be from the lower gear housing seals, so I drained the stern drive and checked the lube. It seemed ok, fairly clear, so I tested some of it by adding a little water. Then some new lube to check the difference. There was a little difference but not the same as if there was a lot of water adding to it.

Would anyone be able to advise the hotspots for this leakage so I can investigate fully?

Kind regards
English Mariner

Re: Oil slick whilst engine running

Is it an actual oil slick, or just a rainbow? The rainbow could also be gas from a very rich or flooding carb at idle.

Pull the plugs and read them, are they oil fouled or wet with gas?

Re: Oil slick whilst engine running

Arrr, yes of course......a rainbow of gas/petrol. It could well have been. I did overhaul the carb last year, I didn't think to check the plugs though...deeerrrr!!

Don, it was at idle, but I had checked the float levels during the overhall and replaced all the necessary bits.

Re: Oil slick whilst engine running

Just because you throw parts at something, doesn't automatically make it good. How does it idle? A 5.7 running good should idle smooth as silk at 600 rpm.

How about the clear hose from the fuel pump to the carb, any gas in it?

Re: Oil slick whilst engine running

She idles well for a 4.3 V6 and I had checked the clear tube previously, but not when she was slicking. I guess this is sometihng I need to do.

I was just about to order a lower gearbox seal kit!!

Don, this might seem a stupid question but if it were oil, what would the difference be?

Re: Oil slick whilst engine running

1988 engine in salt water (maybe ?)

i'd check for water in the cylinders in the process of eliminating things.

Re: Oil slick whilst engine running

Hmm, yes could be.

Thats more difficult to check I think. Plus having changed all the exhausts and elbows, it would then have to be something like a weak head or block leaking!!

Re: Oil slick whilst engine running

If you had water in the cylinders (even one), it wouldn't idle or run very well.

Re: Oil slick whilst engine running

Oracle by the Sea.....I can understand why you got that title....water entering into the cylinders would cause missfires!

Don, wave your magic wand here for a moment. I'm 30mls from water, if I were to start her up on muffs, what should I look for?

Re: Oil slick whilst engine running

English Mariner said:

Oracle by the Sea.....I can understand why you got that title....water entering into the cylinders would cause missfires!

Don, wave your magic wand here for a moment. I'm 30mls from water, if I were to start her up on muffs, what should I look for?
Would anyone be able to advise the hotspots for this leakage so I can investigate fully?

Click to expand...

Ayuh,... Why start it,.... I thought yer lookin' for an Oil Leak,..??

All that takes is Lookin',.....

Re: Oil slick whilst engine running

Possible power steering cooler leak?

Re: Oil slick whilst engine running

Pull the plugs and look at them
If you see rust or water on the plugs, then you have water getting in.
If you see oil on the plugs, you have oil coming in from somewhere.
If you see gas, then you have gas/flooding/too much gas for some reason.

Which one is YOUR problem? You have to look, we can't.

Re: Oil slick whilst engine running

Ayuh,... Why start it,.... I thought yer lookin' for an Oil Leak

And y'know, for the DIYer this is not obvious, but now you mention it, it is However with all that water going through it a small leak would be difficult to spot.

Check the plugs! I see! Thank you!

Re: Oil slick whilst engine running

English Mariner said:

Ayuh,... Why start it,.... I thought yer lookin' for an Oil Leak

And y'know, for the DIYer this is not obvious, but now you mention it, it is However with all that water going through it a small leak would be difficult to spot.

Check the plugs! I see! Thank you!

Click to expand...

With her sitting on trailer, or stands, run the trim up and down a couple of times and look for oil on the rams, cylinders, hoses. No oil, then that's not your problem. Look and see if there is any drive oil leaking around the drive seams. Lots of stuff to check while sitting high and dry.

As Don stated, pull plugs and check them to see if anything is strange about them. Manuals will tell you what to look for and point to a direction to check further. Reading plugs and knowing what you are looking at can be like reading a crystal ball (Um... Don) and they can tell a true story. Even running your finger thru the black soot in the exhaust and smelling it can tell you some things if there is a problem. Strong smell like petrol, feel oily?????

Re: Oil slick whilst engine running

My rainbow was caused by a leak in the inline raw water cooled oil/power steering cooler. I removed and pressure tested and sure enough, had a leak. Replaced and all's been good.

Re: Oil slick whilst engine running

Oh dear, this is completely embarrasing.

My son seems to think that although it was a Rainbow, it appeared after, we had turned the engine off.

Therefore my thoughts turned to flappers not working properly etc etc.

That being the case, I'll check the plugs. So apart from the obvious things I should look out for, what are the not so obvious things I should look out for?

Oldbold
Your solution does seem logical!