Mercury 1988 175 hp Black Max overheating.

M

merlebh

Cadet
Joined
May 29, 2012
Messages
8
My 88' model 175hp Merc overheats at mid to high speeds. It does not overheat in neutral at high rpm's. That leads me to believe it is a turbulence/cavitation issue. I have lowered the motor as low as I can with the jack plate that is installed. Still, the cavitation plate is well above the bottom of the boat's hull. My boat is a 1994 Javelin. My thinking is this boat was designed for use with a long shaft motor, probably Evinrude.
Does my thinking seem logical?
What would be involved in converting this motor to a long shaft configuration? Is this feasible or even possible?
Also, any ideas on a different jack plate such as a paraglide?
I appreciate any ideas or input.

Just for reference: new impeller and stats last season.
 
J

jigmister

Petty Officer 1st Class
Joined
Dec 25, 2007
Messages
203
Re: Mercury 1988 175 hp Black Max overheating.

poppet valve? restriction in the cooling system? only takes 30 seconds running out of water to destroy impeller installed yesterday.
dose the boat have a water pressure gauge? what is the pressure if so

waterpump base and housing?

sure its really overheating or is it a false reading or flase alarm?




just alot of thing to think about.
 
M

merlebh

Cadet
Joined
May 29, 2012
Messages
8
Re: Mercury 1988 175 hp Black Max overheating.

jigmister said:
poppet valve? restriction in the cooling system? only takes 30 seconds running out of water to destroy impeller installed yesterday.
dose the boat have a water pressure gauge? what is the pressure if so

waterpump base and housing?

sure its really overheating or is it a false reading or flase alarm?




just alot of thing to think about.
Click to expand...

I've had the poppit valve apart. Replaced bellows plate and valve seal. By watching my water pressure gauge I'm certain the poppit is working correctly. There is a pressure drop at higher RPM's. The tell-tale stream is putting out water (small stream at idle and heavier stream at high RPM's). I have checked the cylinder heads with a temp/melt stick to verify it is actually overheating and not a false indication. Both heads are getting hot.
 
J

jigmister

Petty Officer 1st Class
Joined
Dec 25, 2007
Messages
203
Re: Mercury 1988 175 hp Black Max overheating.

your on top of it then. I would try a impeller and water pump assemble just to be sure.
 
M

merlebh

Cadet
Joined
May 29, 2012
Messages
8
Re: Mercury 1988 175 hp Black Max overheating.

jigmister said:
your on top of it then. I would try a impeller and water pump assemble just to be sure.
Click to expand...

Yes I've order new poppit parts and going to put a water pump kit in it before I spend the big bucks on a conversion kit.
 
M

merlebh

Cadet
Joined
May 29, 2012
Messages
8
Re: Mercury 1988 175 hp Black Max overheating.

Well, I took some pics on my phone this morning before work then realized it won't let me upload from my phone. Is there a way that you know of? Otherwise I'll have to wait a couple days til I can upload to my PC.
 
C

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Mercury 1988 175 hp Black Max overheating.

Double check WOT timing and that the timing lever moves freely throughout its travel range, as sticking causing retarded timing will overheat.
 
M

merlebh

Cadet
Joined
May 29, 2012
Messages
8
Re: Mercury 1988 175 hp Black Max overheating.

Thank you, Charlie. I'll add that to my to do list for this weekend.
 
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