Oil in the Exhaust

[Ken M.]

I have 7.4 L Mercruisers with about 900 hours each. I've noticed oil drops in the water when running the engine in the slip. It seems to come from the exhaust. I also noticed the engine eating oil, so I'm guessing the slick is oil and not raw gas.

Any ideas?

Ken
1975 FBC

[Navatech]

I also noticed the engine eating oil

Please define "eating oil" quantity wise... Every engine will eat some oil... That's normal... It's only when the quantity is excessive that it becomes cause for concern...

One other thing, normally oil in the exhaust would burn up... So please specify exactly when it shows up...

[John F.]

Take a look at your engine oil coolers and transmission oil coolers

[Bruce]

John is right, coolers first.

[Ken M.]

Thanks very much for chiming in on this. I truly appreciate the input. I just inherited this boat. My father was the original owner. As a kid, I went with him to buy it new. While I've been running it since 1976, I've never had to deal with the mechanical maintenance, so the input from this forum is both welcome and comforting.

I've been adding 1-2 quarts every 10 hours or so based on a noticed drop in oil pressure. After adding the oil, pressure returns to normal. I notice the slick whenever the engine is running (and I'm not moving).

I'll absolutely check the coolers, but forgive the ignorance ... what am I checking for?

I'm pretty handy, but I'm not a mechanic.

Again, thank you!

Ken

[Rawleigh]

They will need to be pressure tested.

[Navatech]

I've been adding 1-2 quarts every 10 hours or so based on a noticed drop in oil pressure. After adding the oil, pressure returns to normal.

That IS excessive oil consumption... Plus you're relying on a single sensor... If that sensor fails you could lose the engine... In addition, if it is the oil cooler (as suspected - see below) then you could get seawater in your oil pan... Not good!...

I notice the slick whenever the engine is running (and I'm not moving).

To me that means the leak isn't coming from the engine (e.g. faulty valve stem seals)... That oil would mostly burn up... I'd go looking at your oil cooler... ASAP!...

what am I checking for?

The cooler is basically a heat exchanger... Tubes in a package through which the hot oil runs... These tubes have cool seawater flowing on their outside... Thereby the oil gets cooled on the inside... Just like a radiator except that you have oil rather then water in the pipes and you have water rather then air on the outside...

What happens is that due to corrosion a fault is created through which oil can mix into the water... As the oil pressure is usually greater then the cooling water pressure it's the oil that leaks into the water... However, under certain operating conditions this may not be true and then you're very close to ruining your engine... Not good!...

There's really nothing you can look for yourself as the leak would be internal to the cooler... You need to dismantle the cooler and take it to a pro... Preferably one that has experience with marine coolers but an automotive radiator shop will also do in a bind...

I'm pretty handy, but I'm not a mechanic.

Mechanics aren't born... They learn the theory and then build up experience... The members can help with the theory... For experience you'll need to get (literally) down and dirty :-)

The cooler will have one inlet and one outlet each for both the cooling water and the oil... Some of these might be integral to the engine/cooler and some might be just hoses connected to the cooler... A "pretty handy" person should have no problem... Just like a "pretty handy" person should have no problem taking a radiator out of car... I have no idea what engines you have so unless you post a picture or provide that information I can't be more specific...

[lobsta1]

What happens is that due to corrosion a fault is created through which oil can mix into the water... As the oil pressure is usually greater then the cooling water pressure it's the oil that leaks into the water... However, under certain operating conditions this may not be true and then you're very close to ruining your engine... Not good!...

I can definitely vouch for water entering into the oil pan. A few years ago,started winterizing & I changed oil & filter on both engines. It was late so figured I would come back next day for fogging & antifreeze. Next day checked oil level before I started & found that the port oil looked like cappucino.

I've always gone on the 8 year plan of replacing coolers. I was due in the spring. Looks like I better plan on a 7 year schedule from now on. The oil cooler was just scooping raw water into the oil flow. No sheen on the water outside. New cooler in & 5 oil & filter changes later the oil was back to clear. If I hadn't been late the 1st day & done my winterizing, I would have been looking for a new engine in the spring.
Al
P.S. Your cooler will look something like this. Lenco is also a good place to buy from.
http://www.lencocoolers.com/2.htm

[John F.]

I replaced the engine oil coolers on my 454s because I thought I saw a little sheen on the water when idling around, I had no idea how old they were, and the replacements from Lenco were relatively cheap. My advice would be to just replace them, unless you know that they're relatively new.

[Navatech]

Good points on the replacement issue... I come from a background of BIG commercial ships (think along the lines of Panamax and even Postpanamax box carriers) and replacing coolers is something we try to avoid... Having said that, considering the cost of new coolers for your boat AND considering the potential for major damage to your engines replacing your current oil coolers is both financially valid and entirely doable as a DIY project for any person... Even one just barely handy with tools...

Make sure to get new MARINE hose clamps and put TWO on each end... Offsetting them is also advisable!...

BTW, if you're going to do the one do the other also as, assuming they're the same age, that one is sure to fail very soon...

[Ken M.]

You guys are incredible. Can't thank you enough for the input. The engines are 454 Mercruiser 7.4 Litre OPP. They're fresh water cooled. Does that change the advice?

I'll take pics when I get down to the boat this weekend.

Thanks again.

[STraenkle]

Nope, Oil coolers are on the raw water side

[Navatech]

The engines are 454 Mercruiser 7.4 Litre OPP. They're fresh water cooled. Does that change the advice?

Not really... I'm not very familiar with marine gas engines but I would think that while the engines are FW cooled the oil cooler is still RW cooled... In theory you could run the engine's FW cooling water through the oil cooler but it would complicate the system... And you'd still need the same total cooling capacity which means a bigger FW/RW heat exchanger (cooler)...

[Rawleigh]

+1 for Lenco. I bought replacements for my 440's from them. Get the cupronickel ones for longer life.

[Ken M.]

OK, a bit embarrassed here....You've got me sufficiently concerned so I went down to the boat today to look into the oil cooler situation. I don't believe I have oil or transmission coolers. Old lines appear to go from the pump through the filter and back into the block.

Could it be something else, or am i just looking in the wrong place? I took photos and will upload them and provide a link tomorrow.

Thanks again...

[Pete Fallon]

Ken M,
Look at the hoses coming off the sea water pump they are 1-1/2" hoses, they run aft to the oil cooler, on the 7.4 l 454 engines they are usually just above the transmissions they are about 2" around with 2 black hose oil lines with metal fittings coming off of them. They are about 12" long with flared ends on the coolers. I would hire a good Mercruiser mechanic to go over the engines for a couple of hundred bucks its well worth it. As for the decks find a good fiberglass shop in your area and show him what is needed. make the decks out of high density foam covered with layers of 1708 and 1808 fiberglass cloth.
Pete Fallon

[Ken M.]

I never did say thank you to all who chimed in to help. It absolutely was the oil coolers. I replaced them with the Lenco units. Problem solved. This one, anyway. I truly appreciate the wisdom on this forum. Thanks so much.

[Craig G]

If your Mercruisers are about 1995 vintage, you might have a 3 in 1 combination heat exchanger for engine along with oil and transmission cooler installed in the front of the engine. They only did that for about a year. It looked good, but was a bad idea as In obsolete now if you need replacement. I re-engineered my entire cooling system with a custom made heat exchanger and off the shelf oil and tranny coolers mounted remotely when one of my oil coolers leaked after about 15 years. Now my oil and tranny coolers can be replaced for about $100 each with about an hour of work.