The Saga Continues... High water pressure causing overheating. 2.5

[DieselDood]

OK, so I've been fighting this for a while now.

1996 Mercury 2.5 on my 1985 184 Champion Bass boat. I rebuilt it 2 seasons ago now (spring will be it's 3rd). It only has like... 75 hours on it. At the time of rebuild EVERYTHING was new. Poppet, water pump, thermostats, gaskets, etc.

The issue is this.
If there is any floating debris in the water when I use the boat, the next time out, the water pressure will peg my gauge at WOT, and in... about a mile it will get beyond 175 cylinder head temp. (new sensor and gauge)

I can take it home. Pull the poppet apart. Usually I find a very small pebble in it. Roughly... the size of the ink inside a pen, but round. I clean it out. Flush it out with the hose. Put it back together and head to the lake.

All is good. Poppet functions as it should, opening, keeping the water pressure at around 22psi and my cylinder head temp stays under 170. It does still seem to be warmer than I thought it was supposed to get, but when all is "right" 170 seems to be the happy place.

Pull into the busy landing where the muck is stirred up... put it on the trailer... go out the next time and it's pegging the gauge and running hot again. I'm tired of EVERY TIME I bring the boat home, I have to pull the poppet, clean and flush it.

SO... I'm going to replace all the poppet parts again. I'm going to replace the Thermostats. It's been 2 years, so for PM I'm going to replace the water pump.



NOW... I've been debating separating the powerhead from the lower unit to check for issues. I have read: "the passages in the rear divider and the drain area at the base of the powerhead" can be a problem. Can anyone show me a picture of what I'm looking for when I take this apart and try to check these locations? While I have the motor off the lower, is there anything else I should be checking as well?

Also when looking up the water pump I found there are 2 potential options. 18-3317 and 18-3316 Does anyone know what the difference between those 2 water pump kits is?

This boat gets used for bass tourneys all summer, so I really can't have it down once the season starts. I'd LOVE to get this fixed so it's just turn-key every week and I don't have to worry about it as much.

[David - WI]

That doesn't sound right, I would guess that cooling system was full of sand & pebbles when you got it... and they're slowly working their way out every time you run it?

[25two.stroke]

Sounds like theres junk in between the 2 pieces of the 2 piece adapter plate. That or the powerhead is on a 2.4L adapter plate and its too temperamental for a 2.5. I can take pics of the divider passages that can get clogged up, but it sounds like theres more of an issue than that. When you take your water pump apart make sure you check the upper housing for melting above the cup and the lower housing (wp base seal) for melting below the wear plate. If either of these are melted it can cause the engine to pump enough water when all is well but then as soon as any little thing goes wrong it won't pump enough.

Not sure what the difference between the two sierra numbers are that you listed cause I never use sierra water pump kits, but my best guess is one comes with an upper housing and one doesn't...or one comes with a lower seal carrier/housing and the other doesn't.

[tunnelmike]

I have had debris get into my exhaust divider plate twice (225 pro max) and on other motors (260) at Suwannee last spring. Sometimes they get real warm running and the last time all I noticed was slightly higher water pressure.

[22R]

This thread may be of some help to you.

92 Merc XR6--High water pressure ??? | Allison Owners Forum

22R

[DieselDood]

Thanks guys I'll check these out!

After the rebuild it was good for about a month, then I got into a nasty landing. It was a sandbox in the poppet, so at that time I pulled the lower unit, left the poppet out, pulled the T-stats and back flushed everything I possibly could. When I put it back together everything was good till I got into any even moderate dirty water. Now it's damn near constant.

[rock]

Get a powerhead base gasket and an adapter gasket and pull powerhead. Don't have to disconnect anything just pull powerhead up and swing it out of your way. remove 1/4" and 5/16" bolts and separate plates. probably full of debris. Very simple procedure.

Rock

[DieselDood]

Get a powerhead base gasket and an adapter gasket and pull powerhead. Don't have to disconnect anything just pull powerhead up and swing it out of your way. remove 1/4" and 5/16" bolts and separate plates. probably full of debris. Very simple procedure.

Rock

I plan to do this for sure. I'd like to know where to look as well though.
I may go one step farther, and wait for better weather, pull it out of the way like you said, but with the plates off I'll back flush from the Stats and the Poppet, just to make sure EVERYTHING is out.

[rock]

Once you are there it becomes rather obvious. Be sure to disconnect the shift linkage so you don't pull it out with the powerhead. Any questions you can call.

Rock