Overheat Update & Exhaust Plate ?

[forceboy]

I took off my exhaust manifold on the weekend and discovered my gasket (my brand new gasket) is shot. May have been my fault - did not have an inch-pound torque wrench so I kind of guessed at torque. I am hoping this is the source of my overheat/low pressure problem. My question is what is the purpose of the exhaust plate? My motor never had one - should it? Would it not stop proper exhaust flow? Motor is an 85HP L-drive - all motor breakdown drawings I have show the plate, but I was also told not all Force motors came with them.

 

[pnwboat]

Re: Overheat Update & Exhaust Plate ?

Exhaust plate is used to form a water jacket to cool the exhaust in the non L-Drive motors. The cover on the non L-Drive motors is very close to the actual exhaust ports. Without the exhaust plate to form a water jacket, I suspect that the aluminum exhaust cover itself would get too hot.

The cover on the L-Drive motors sits farther away from the ports and has the cavity for the water jacket cast into the cover itself. No need for an exhaust plate. Both versions circulate water through exhaust cover to help cool it and provide a water path that feeds the block itself.

All the L-Drive exhaust documentation that I see on-line does not show the exhaust plate.

P.S. Bad gasket is probably why you're not seeing good water pressure. Another note....hose #11 at the back of the adapter plate is where the water exits the block after circulating through the block and head. Sounds like you are getting some water flowing through the block, just not enough.

 

[forceboy]

Re: Overheat Update & Exhaust Plate ?

May have had a breakthru! Most of the water, after circulating thru block and exhaust, flow thru a water jacket that goes to the end of the exhaust manifold and out four 1/4" diameter holes at the tube end of exhaust manifold - the manifold has four plugs at the tube end. I now believe these plugs are cleanouts - my exhaust was plugged up with crap - water would have gone thru by-pass but not out exhaust hose. Hence, it would keep engine cool at idle, but not WOT. Going to put exhaust back on and give it a try. I'll try and post some pics in case others are facing similar issues.

 

[pnwboat]

Re: Overheat Update & Exhaust Plate ?

Sounds like you're making some headway. Certainly getting a good education on the water flow on the L-Drive set up! Keep us posted.

 

[forceboy]

Re: Overheat Update & Exhaust Plate ?

More than you know! I think I am going to know more about these engines than most marine mechanics!

Digging a little more, found out that water does not flow out of exhaust manifold. Sealed chamber - only comes out bypass to keep exhaust hose cool??? In and out must come from head/adpater plate. Hmmm...., back to the drawing board.

 

[pnwboat]

Re: Overheat Update & Exhaust Plate ?

Well I wouldn't say back to the drawing board just yet. The bad exhaust cover gasket would definitely affect water flow and pressure.