HELP! Coolant in my exhaust

[NorCal Boater]

Went to the boat this morning to go meet friends at a raft up. Started up the engines and while they were warming up the port exhaust starts to produce a LOT of white/grey smoke. Using my laser thermometer I determined this was not steam. Nor was it oil or fuel.

A friend a few slips over smelled the smoke and says it is antifreeze/coolant. He had the same thing happen to his '91 370da with the same engines and he said he had to replace the exhaust manifolds.

The engines have 620/622 hours and if the manifolds need to be replaced, no problem. But I have a couple of questions:

1. Could the elbows cause this as well?
2. How can you tell if its manifolds or risers/elbows?
3. I was told if I need to replace one engine I should do both. Yes or no?
4. Should elbows be done at the same time?
5. There are several brands on the market. Sierra, Osco, Gill, GLM, etc. Are there brands to stay away from or are they all OK?
6. Is there anything I am forgetting to ask?

Thanks in advance for the assistance.

 

[tobnpr]

Could be the heat exchanger, or a head gasket. Does the closed cooling side of your engine extend into the risers and manifolds? Manifolds maybe- but risers generally not.

How much coolant have you lost?

I'd pressure check the cooling system.

 

[FireIsland1]

could be head, manifold, heat exchanger, intake manifold. I would pull some spark plugs and take a look.

 

[NorCal Boater]

Thanks for the responses. I ruled out the heat exchanger because the antifreeze is burning off in the exhaust and causing the smoke. A head gasket is definitely possible but with only 600 hours it seems unlikely.

I will pull plugs next weekend and see what I find.

I am still waitng for advice on manifold brands if I go that direction.

Thanks again.

 

[fc3]

Assuming that your closed cooling system includes the exhaust manifolds, then that is the most likely cause of a the problem. You should drop the manifolds ASAP because that coolant is sitting in the exhaust ports and will enter the engine via any open exhaust valve.

Use only Mercruiser manifolds. I tried Osco as did a friend. We both thought that the third party parts were garbage. Despite them being less expensive than OEM, they were overpriced for the way worked.

Best regards
Frank

 

[Coastal Manifold]

Stainless Steel one-piece Manifolds are the best on the market. You can add HP to your boat and in your case with dual motors you can loose around 200lbs off your boat. Your already fast boat would be faster. I can price out your manifolds with a little more info about your boat. Drop me a line.

 

[NorCal Boater]

Assuming that your closed cooling system includes the exhaust manifolds, then that is the most likely cause of a the problem. You should drop the manifolds ASAP because that coolant is sitting in the exhaust ports and will enter the engine via any open exhaust valve.

Use only Mercruiser manifolds. I tried Osco as did a friend. We both thought that the third party parts were garbage. Despite them being less expensive than OEM, they were overpriced for the way worked.

Best regards
Frank

Frank,

Thanks for the response. Are the manifolds typically part of the closed cooling system? If they are then the manifolds are most likely the source of the leak. I was considering pulling them and having them pressure tested.

Shawn

 

[johngus]

use only mercruiser parts.

 

[fc3]

Stainless Steel one-piece Manifolds are the best on the market. You can add HP to your boat and in your case with dual motors you can loose around 200lbs off your boat. Your already fast boat would be faster. I can price out your manifolds with a little more info about your boat. Drop me a line.

I'd like to see a photo of the SS mainfolds for a 1999 Generation VI 7.4 MPI.

Frank,

Thanks for the response. Are the manifolds typically part of the closed cooling system? If they are then the manifolds are most likely the source of the leak. I was considering pulling them and having them pressure tested.

Shawn

Merc sometimes made the manifolds part of the closed system and sometimes made them raw water cooled. Just Ducky has raw water cooled manifolds. I guess they wanted to cheapen the heat exchanger. If you only have one hose at the bottom of the manifold, they are raw water cooled. If you have two hoses on the manifold and one to the elbow, they are closed cooled.

The best way to inspect the manifolds, I think, is with a bore scope. There's typically a plug at the top of the elbow for an oxygen sensor. You can remove the plug, slide in the 'scope, and inspect for water. I ordered a 'scope on Sunday for this purpose. Will let you know how that works out.

Best regards,
Frank C

 

[Coastal Manifold]

The 7.4 Manifold pic is on the yellow boat.On our Web site. The newer 8.1 right below the 7.4 pic The newest 8.1 with all the extra mounts on the Manifold pic will be posted soon. http/www.hi-tekproductsofaustralia