1988 Black max 200hp overheating

[transomstand]

A couple more questions should I run it with the tstats and poppet valve? I also put a different lower unit off a Mariner 150 i was wondering if that could be some of the problem? Any and all help would be appreciated.

The 150 gearcase probably has 2:1 gears in it (a 225 Promax has 1:87 to 1) not a huge issue and makes no difference in respect to cooling. The Promax is designed to run with stats, a poppet and a 2 piece exhaust plate, it's a "consumer" high performance motor not a race motor. Race motors have 1 piece exhaust plates no stats or poppet, turn a bazillion RPM and blow up a lot. 2 million idiots in this world yank the stats and poppet in a fishin motor "cause that makes it a race motor" but it doesn't, however it does make them blow up.

All that said, you're in a tough position. You have a great short block but it's an EFI motor converted to carbs. A motor like this needs somebody with lots of experience to get it sorted.

I would start with a good water pressure and temp gauge (verified with a heat gun on the heads). Replace the water pump assembly (never overlook the simple stuff). Post your temps and pressures at idle, 3000 RPM and 5500 or so if it's not running too hot.

Next I would shop for a 225 Promax exhaust plate that's not been molested. The exhaust plate sits under the powerhead and shouldn't be confused with the exhaust divider that sits under the coils.

Once you've done that you'll have a chance to straighten this thing out. The reason somebody ran this with no stats or poppet is because they were created a massive compensation for some other design error in the Frankenmerc process.

[Baker343]

That was well explained and great advice. Transomstand could he use a gen 2 or 3 2L two piece exhaust plate and either shorten the tuner or replace with a 200 or Bob's tuner

[transomstand]

That was well explained and great advice. Transomstand could he use a gen 2 or 3 2L two piece exhaust plate and either shorten the tuner or replace with a 200 or Bob's tuner

Certainly possible but in this case I'd want to get known correct stuff under it for a start. Just makes it easier to figure what other surprises might be there.

[whitehead249]

Alright I’ll try the easy stuff first and go from there. Is the 225 pro max exhaust plate about 700$?

[transomstand]

Alright I’ll try the easy stuff first and go from there. Is the 225 pro max exhaust plate about 700$?

Wouldn't surprise me if it was for a new one but I gotta think you could do a LOT better than that for a clean used one.

[David - WI]

Isn't there a grommet/bushing in the bottom of the exhaust plate that seals the water tube... seems like people lose or forget those and can never build water pressure?

[Baker343]

I believe it's the same one that's in the impeller housing

[transomstand]

Isn't there a grommet/bushing in the bottom of the exhaust plate that seals the water tube... seems like people lose or forget those and can never build water pressure?

Yes, and all that needs to be looked at. We need pressure readings to see if it's leaking or plugged up someplace.

[transomstand]

I believe it's the same one that's in the impeller housing

Correct

[rock]

Very common for one to be missing.

Rock

[whitehead249]

Alright thank you guys. It sit for a while and had some mud dobbers on it. I’m gonna order a water pressure gauge and temperature gauge. Where should I start with checking the passage ways and make sure there is no debris inside them?

[transomstand]

Alright thank you guys. It sit for a while and had some mud dobbers on it. I’m gonna order a water pressure gauge and temperature gauge. Where should I start with checking the passage ways and make sure there is no debris inside them?

That would require a good amount of disassembly. Under the powerhead in the exhaust plate can be full of crap or in the feed passages in the block behind the exhaust divider plate. If it was me, I'd wait to see what pressure you have first. High pressure would indicate a blockage. Low pressure means a leak or just dumping too much water through ignorant modifications, or an intake restriction below the water pump.

I would drop the gearcase and start with a full inspection down there. Replace the water pump assembly and inspect all the intake passages, check the copper tube for leaks and insure the seal is in place on both ends of it.

Also post some photos of the cooling hoses on the powerhead so we can see how they're configured.

[whitehead249]

Alright I’m going down tomorrow to work on it I’ll take pictures then

[whitehead249]

[whitehead249]

I plumbed it the same way as the old motor that blew up on me