Mercury 500 cooling problem, ideas?

[mmf]

Restoring an older 1968 Mercury 500 (50HP), serial 2407450.
Have the engine running good now so I moved on to the lower unit
to replace the water pump out of general maintanance and a weak stream. Re-installed foot end and ran engine several times. Pee water is steaming, hot. Have a good stream about 700-1000 rpm (still hot) but not a whole lot at 500 rpm idle. Engine block had a 1/8" pipe plug at the top of the block close to the exaust cover so I removed the plug to check water flow thru block when running and it does. Exaust cover gets real hot when run only for a few minutes. I am wandering, could there be a clog or sediment build up inside the exaust cover baffle that could be causing the overheating? Has anyone had any similar problem with the exaust baffle portion of the cooling system?
Any help or ideas appreciated!

 

[mmf]

Re: Mercury 500 cooling problem, ideas?

Forgot to say that I do have good water spitting out of the two exaust ports at the rear leg. Correct me if I'm wrong, but water flows thru the baffle plate passages, does it not?

 

[emckelvy]

Re: Mercury 500 cooling problem, ideas?

Most of the time it's an issue either with a partially restricted water supply tube (busted impeller vanes), or sediment buildup in the large water passages of the block (accessed by removing the cover over the spark plugs).

Definitely shouldn't have a hot telltale. These motors have no thermostat so the water is going right thru. Exhaust manifold cover getting hot means you either don't have enough water supply into the motor, or water is having trouble getting out.

If you pulled the lower unit, you could hook a water supply up to the copper water tube to see what kind of circulation you get thru the motor.

If you get way better flow with an external water source, there may yet be a problem with the pump (worn pump insert, worn pump plate, clogged intake, etc).

If you're still not getting good flow, try removing the block cover and flush water thru the motor. It should gush out the block.

If you'll search thru past posts, you'll find a number of 50HP discussions about cooling issues which may help guide you to a solution.

HTH & keep us posted.............ed

 

[mmf]

Re: Mercury 500 cooling problem, ideas?

Most of the time it's an issue either with a partially restricted water supply tube (busted impeller vanes), or sediment buildup in the large water passages of the block (accessed by removing the cover over the spark plugs).

Definitely shouldn't have a hot telltale. These motors have no thermostat so the water is going right thru. Exhaust manifold cover getting hot means you either don't have enough water supply into the motor, or water is having trouble getting out.

If you pulled the lower unit, you could hook a water supply up to the copper water tube to see what kind of circulation you get thru the motor.

If you get way better flow with an external water source, there may yet be a problem with the pump (worn pump insert, worn pump plate, clogged intake, etc).

If you're still not getting good flow, try removing the block cover and flush water thru the motor. It should gush out the block.

If you'll search thru past posts, you'll find a number of 50HP discussions about cooling issues which may help guide you to a solution.

HTH & keep us posted.............ed

Thank you for the reply, I will remove the lower unit and try running water thru the copper tube and see what I have then, I would much rather remove the cover at the spark plug area than the exaust cover after reading all of the "broken off bolt stories" I have read about!

You say it's possible the water is not "getting out", does the water leave the block in the exaust cover area?
Yesterday, after I made the post I made a "water adapter" so I could run some water into the block thru the 1/8" pipe hole at the top of the block while the engine was running (the top of the block seems much hotter than the bottom of the block). With this setup, the pee stream cooled off to just warm water and the temperature of the exaust cover was reduced alot as well, but the exaust cover was still pretty warm even though I could hold my hand to it for awhile.

I do know that my copper tube is clear because I had the power head off and removed the tube to clean the exaust soot from it. I changed over the complete lower section of the motor to convert it to a long shaft motor from a short shaft. I installed new power head gasket and exaust (leg) gasket when I moved the powerhead.

I am wandering about the "volume" of the water the pump is putting out. When I replaced the impeller, I carefully inspected the SS plate and upper cover insert and did not find much wear at all except a little groove where the impeller brass hub wraps around the driveshaft. I did not think this would warrant replacement of the plate, maybe I'm wrong. How much wear (0.XXX) would be allowable in this area?
The upper water pump housing on the foot end I am using (mid 80's "Mercury Classic 50"), does not incorporate a seal in the housing, only a centrifugal "slinger" on the driveshaft that sits on top of the upper housing. I thought this a bad design by mercury and a possible area for a water "leak" from the pump area, just thinking.
Sorry to ramble on so much, but I would like to get more experienced opinions of the problem at hand........thanks

 

[mmf]

Re: Mercury 500 cooling problem, ideas? problem found

Re: Mercury 500 cooling problem, ideas? problem found

well, I think I have found my problem! I hope this will alert some other person that has similar problems in the future.

First, I did the direct water test to the copper pipe that goes to the power head.....connected hosepipe and ran engine......pee water temp cool!....exaust water barely warm!....exaust cover, cool as a cucumber!

So, I took lower unit inside to do my inspection of the water pump assembly again.....First, I found out that I was previously wrong about there being no seal in the upper housing, there is one, mine is so hard and worn that it looks like part of the housing plastic!.......next, the big shocker and I'm sure the real water supply problem I was having is, someone (previous owner of lower unit) had put a lower water pump base in that had a water flush passage in it, problem is, my lower unit had no screw, nor had it been drilled for this on my unit!....so the lower housing had about a 1/8" clearance between the "flush hole" in the housing and the inside of the foot casting when in place (installed position) which was allowing the output from the pump to shoot half of the water out this hole! .....no wonder it did not have enough water to the head!!!..........
I will get the proper housing parts, gaskets etc, and install and report back my findings as soon as I can.

Thanks for the help! I sure am glad I did the hose pipe, copper line check before I needlessly tore in to the exaust cover or rear cover!
Saved me a bunch of work!

 

[achris]

Re: Mercury 500 cooling problem, ideas?

Well done and well spotted on the flush hole base... I use the 'hose up the copper tube' trick a lot... Even on Mercruisers with the leg off... I stuff the hose in the water hole in the bell housing and run 'em up.... Excellent diagnostic tool... Simple, effective and direct!

Chirs....