1983 Johnson 115 - Oil on the Outside of the Exhaust Housing

[Greg Mrozinski]

Hi forum members. Need your help. I have a 1983 Johnson 115 on my resto project. Engine runs well with the exception of WOT is only at 4900 rpm. I notice after running for awhile there appears to be a little oil running down the outside of the exhaust housing between it and the rear cover. Do I have a small exhaust leak at either the adapter to power head gasket or inner exhaust housing gasket? If so will this effect WOT performance? Prop is the standard prop (I think 17x19). Thanks for your help.

 

[emdsapmgr]

Re: 1983 Johnson 115 - Oil on the Outside of the Exhaust Housing

These engines have been known to fail the powerhead base gasket. Not unusual on crossflows that have a lot of hours on them. You can verify it by running the engine up to normal temps with the cowling off. Usually that oil is a mix of unburned fuel and exhaust residue. If it's the base gasket, you should also see some smoke inside the cowling. While it looks messy, it's not a prelude to imminent failure. You should get is repaired sooner rather than later-any exhaust smoke inside the cowling will get re-ingested in the carb throats as you run the engine. Not a good idea long term. The fix is to pull the powerhead-replace the gasket. Your engine should run at least 5500-5700 with the right prop. Likely your prop is really a 13X19. If you drop to a 17 pitch, you will pickup about 300 rpm's and increase your torque. Even with that change, your rpm's would still be considered "low."

 

[Greg Mrozinski]

Re: 1983 Johnson 115 - Oil on the Outside of the Exhaust Housing

Thanks emdsapmgr. I really appreciate your input. I will remove the cowling and check it out. You are correct that it looks like a mix of oil and exhaust blackish type oil. There is not a lot of it but it does weep down during the day and after I run it. Yes I understand about the prop. I wanted to ask the question about the gasket first to make sure there wasn't a back pressure issue causing a loss of power perhaps. I will also swap the prop to get the rpms up. Thanks again.