Outboard water pump liner spinning issues.

[Sidewinderdan1979]

Hello, I have a 1975 Mercury 1500 150hp that I've been chasing overheating issues with. I've done the water pump twice this season the water tube and I've cleaned the water jacket and put a new gasket on.
Yet I'll still get up to 200f on the jacket, block and exhaust baffle.
As of now I'm wondering if maybe the water pump liner is spinning or possibly the timing is to advanced. I'll be checking the timing today and checking the water pump yet again. But I'm truly lost on why she's overheating.
Compression is 140-145psi across all cylinders.
Also, when it does overheat I'll just put ut in neutral and within 5 mins everything is back down to 130f range. All temps have been taken with 2 different digital thermometers to confirm accuracy. Please help. Any advice would be great.

[Jim Speros]

I think if the water pump liner was spinning it would be obvious. It would melt the plastic housing.

Do you have a water pressure gauge? It seems to me that if it cools at idle the pump is working properly and the water tube grommets are sealing.

Proper cooling needs both water in and water out. I would check to see if you have too much pressure at speed.

Another way to check flow is to remove gearcase and attach a water house to water tube. It should accept a significant flow of garden hose pressure.

Any and every 2 stroke should have a water pressure gauge.

[WaterZebra]

Hello, I have a 1975 Mercury 1500 150hp that I've been chasing overheating issues with. I've done the water pump twice this season the water tube and I've cleaned the water jacket and put a new gasket on.
Yet I'll still get up to 200f on the jacket, block and exhaust baffle.
As of now I'm wondering if maybe the water pump liner is spinning or possibly the timing is to advanced. I'll be checking the timing today and checking the water pump yet again. But I'm truly lost on why she's overheating.
Compression is 140-145psi across all cylinders.
Also, when it does overheat I'll just put ut in neutral and within 5 mins everything is back down to 130f range. All temps have been taken with 2 different digital thermometers to confirm accuracy. Please help. Any advice would be great.

I know this sounds kinda dumb, but what is the telltale relief tube outlet doing? If nothing is coming out of it you have an obstruction somewhere. It is steaming, there is a supply problem somewhere. Is there water coming out of the "nostrils" at the top of the mid section? There is a poppet valve at the top of the block. Check to see if the spring is stuck. Try running the engine at WOT without the poppet spring but use a washer as a flow restrictor. We use this set up for racing a lot.

[Sidewinderdan1979]

I May have figured it out. I've never checked the timing on this motor so yesterday I checked ut and she was at 27°!!! Max for this motor was 21 back in the day and with new fuel 20° is recommended as the max. So I set it to 19° and I. about to take it out in about an hour and see if I've solved it. Kinda have my hopes up.

[WaterZebra]

I May have figured it out. I've never checked the timing on this motor so yesterday I checked ut and she was at 27°!!! Max for this motor was 21 back in the day and with new fuel 20° is recommended as the max. So I set it to 19° and I. about to take it out in about an hour and see if I've solved it. Kinda have my hopes up.

Make sure TDC on #1 cylinder is where it should be (flywheel). Put a dial indicator in the #1 spark plug hole and see if the pointer over the flywheel decal matches TDC position. If not, adjust pointer if it is movable. Usually the flywheel and decal are in parity with the crankshaft. Another comparison (to my memory?) is that 0.0150 before TDC is equal to 21 degrees? Make sure your high throttle advance linkage is properly set up (threaded adjustment). What do the spark plugs look like (color)?

[Carter Powell]

.150 before top dead center should be equal to 25 degrees BTDC.

Carter Powell