Our boat is over the winter in a hall. To test stands a large tub with antifreeze and water under the drive. So far, everything OK. After a short test, the (cooling) water turned black. It has a very light film of oil. The oil from the block is OK so far. Here I could find no water in the oil. I'm really stumped woren it is.

Thought of the exhaust manifold, head gasket or crack in the head. Hope it's just a gasket or the exhaust manifold. Is there an easy way to test it? Here have no workshop to test my engine.

It is a 307 Block. I'm really grateful for any tip.

Does the engine have power steering and/or oil cooler ?

Does the outdrive contain the cooling system impellar or is it engine mounted ? If engine mounted does it contain a lube reservoir like some of the Bravo models with mechanical fuel pumps ?

Is the water going into your engine going back into your bathtub set up ?

You could have oily residue in exhaust from worn rings/valves or simply from 'normal' wear.

The impeller is installed in the drive. Therefore, it can not come. Have only one OMC Tru Course Steering. There is not really oil in the system.

Maybe it's really just oil from the oil change on the drive. Then the oil is everywhere in the cooling circuit. The engine has been running with the soup 1-2 minutes. Then I have to first of all "flush" and get out the oil there.

I wanted tomorrow, re-measure the compression. Then I would rinse 1-2 times. The rest will come out in the summer of its own.

what year model and app do you have here ?

well,we know tru -course steering is a stringer omc drive..so it'll be 70's to 80's

If you have the exhaust running through the prop and into your tub, the water is going to get dirty, especially if it is running rich or misfiring.

Its a 307 engine. Recalling GM used this engine 1968 thru 1973 and that's it. OMC used it I think in the early 70's only. Some boat manu;s matched this 307 OMC engine with a Jet drive as well during that timeframe. If I recall it was 245 hp at the crank on the OMC engines. In his post I missed that it was a 307 engine thought it was 305 so that's what I get for reading without glasses on. I hate getting old.

Possible carb rebuild also possible fuel pump diaphragm issue if it has the line dumping back into the carb. Man I can barely remember that engine & set up. I know it had log exhaust manifolds and rear exiting risers. Next - it could be motor oil past the rings issues - wear or poor sealing rings. Just throwing it out there. Leakdown test would be good as well, along with vacuum testing running the engine.

Sorry about the Secret Engine. It is a 1973 307 GM V8 Electric Shifter with 225 HP.

I was testing compression with a small tester. Every cylinder was about 9 to 9,5 bar pressure. I have already ordert a new Tool for texting compression more exactly. I have also already a carb rebuild kit and new sparking plugs here. Will check this tomorrow. I think the Engine runs to rich. You can "smell" the gasoline from the exhaust...

Well at least I had the year range & exhaust manifolds / riser combo right but thought 4 sure it 245 hp at the crank. Where are you located as I am a little lost about your compression testing explanation. Still say possible CARB / fuel related issue. Anyways good luck with it.

Yesterday we tested the Compression. After testing we changed also the Spark plug and an ignition cable. Tomorrow we test again and i will check the fuel lines and the carb.

1---9,2 bar
3---9,8 bar
5---8,9 bar
7---10,2 bar
2---10 bar
4---9,5 bar
6---10 bar
8---10 bar

My tester looks like that: