mercury 200 black max overheating!!!! Please help

[koshlakehydro]

Hello everyone. New to the site and hope some of you can help me. I have a 1984 mercury 200 black max oil injected outboard on my hydrostream. The motor is overheating. Checked thermostats, poppet value, did a compression test and all is fine. Had heat gun on it and defiantly overheating. Seems top of the motor isn't getting enough water, gauge says 5 pounds but don't think I have that much pressure. The guy that is looking at it says exhaust is getting in somewhere and he thinks its coming from lower unit. Lower unit is brand new from merc last year. Any ideas??

[King Dad]

If you haven't check'd the water pump, base, impellor with a fine tooth comb, you should. Nuthing like doing lots of other things related to cooling but never have inspected the one thing that has the most bearing on cooling! BTW, a new water pump from Mercury last year is........... a year old water pump!

[transomstand]

The guy that is looking at it says exhaust is getting in somewhere and he thinks its coming from lower unit.

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This would seem to be a rather bizarre conclusion

Where are you measuring water pressure from?

[koshlakehydro]

he had lower unit all apart and everything seems perfect. He is going to double check it all again today.

[tlwjkw]

he had lower unit all apart and everything seems perfect. He is going to double check it all again today.

First thing...If YOU, YOURSELF don't know anything 'bout tha water pump, as in when, what parts, who did tha job you put a "complete water pump kit" in it at any indication of over heat. Go from there!

[Go Time]

5 psi is very low water pressure for that vintage engine if that is what you have at speed. My old V6s from the 80s ran about 10 psi at idle and 25 WOT.

Even more amazing is that you have a 30 year old oil injected motor.....I'd say you're on borrowed time. I think 1984 was the first year of oil injection. Is it the original powerhed?

[koshlakehydro]

he is going over it with a fine tooth comb today..ill report back

[dompie99]

Been there done that, an overheating issue.

I replaced the pump assembly (water), still was overheating, f
found out that the mid plate between lower unit and engine was not straight, got it straightned and now it works okay.

I found out that the block behing cylinder 5 was welded and that it was ''J B Welded '' on the water passage behind it, grrrrrrrrr

Now I need a new block....

[Onetime]

I agree that 5 psi is not enough.
Two places to loose water pressure and also allow exhaust into to cooling system. Not that I agree with your mechanic who said it was coming from the lower unit, as Heathen said, bizarre!
The exhaust plates could have a deformed gasket or corrosion allowing the water pressure to escape. Depending on where it is could be allowing exhaust gasses in.
The exhaust chest cover is the other spot with the same scenario regarding gasket and or corrosion.

[tlwjkw]

5 psi at idle or wfo?

[Onetime]

Even at idle way to low water pressure for a poppet valve engine, assuming it still has the poppet valve.
With a poppet valve should be 10-12 psi at idle and 20-25 at full throttle(wfo).

[tlwjkw]

Can't remember ever havin' anything idle at 10+ (700 ta 900) when all was right but that's with my junk.......

[eli]

prior owner maybe had impeller go and never found the rubber pieces stuck up in the water tube

[Go Time]

poppets on the old 2.4s were different in the early- mid 80s than the one in the later 80s and 90s

[dompie99]

So in other words, what you guys are saying is, 5psi at idle for a poppet vale engine is way too low ??

what should I expect from a 3.0L V6 225hp merc at idle than ??