1990 Mercury Force l-drive overheating

[bustedbayliner]

I recently purchased this 1990 Bayliner Capri with the Mercury Force l-drive.
It was only needing carb work. ya right. I got the motor started up and dropped it in the water it ran fine at idle but at w.o.t. it set off the overheat buzzer. Pulled the plugs out and found sludge in bottom 2 spark plugs. Changed the impeller in the water pump. it had encountered some heat before. Pulled the motor replaced the 2 gaskets on the exhaust manifold side also the head gasket was replaced and the thermostat.While in the motor i found out the blocked had been bored .30 with wiese pistons installed all cylinder walls looked fine no deep groves anywhere. I installed a pee-shooter on top along with a temperature gauge. Took it to the water everything fine at idle but overheatd again. Temperature gauge has not even came off of 100 degrees and the water was coming out of the pee-shooter. Does anyone know how much water pressure it should have. The whole motor was cool except around the head where the overheat buzzer is. Can anyone give me any idles,suggestions. thank you

 

[pnwboat]

Re: 1990 Mercury Force l-drive overheating

Do you have a 90HP or 120HP L-Drive?

If you have a tach, what is the maximum RPM you are seeing at WOT?

I have a 1988 125HP motor with a water pressure gauge. At idle, around 800 RPM's I see around 6 -7 LBS of water pressure. At WOT 5200 RPM's I see about 18 -20 LBS of water pressure.

If the ignition timing is too far advanced it may cause it to overheat at WOT. It should be no more than 32 degrees advance at WOT. Some folks set it to 30 degrees just to be safe to prevent detonation ( due to poor quality gas etc.).

Also make sure you have fresh gas.

If carbs are running lean, that will also cause it to overheat (and possible melt a piston).

 

[bustedbayliner]

Re: 1990 Mercury Force l-drive overheating

I had the boat serviced and new impeller put it. It does not matter if your at 800 R.P.M.s or 5500 R.P.M it still has the same amount of pressure at the pee-shooter that I installed. I told the service manager that it should pump out more pressure at WOT and he agrees so we are going to try to see iff we have restriction somewhere . He also told me that my timing was fine, but I will ask again. Thanx for your input if you have any more suggestions let me know. I appreciate the feedback on the water pressure because I have been looking for this infomation.

 

[pnwboat]

Re: 1990 Mercury Force l-drive overheating

Have you changed the thermostat? According to what I see, all of the 1990 L-Drives take a 130 degree thermostat. It's kind of hard to find these thermostats. Most common type out there is 143 degree thermostat. You could temporarily remove the one in your motor and run it to see if that has any affect.

The other possibility is a bad temperature sender?

If all of those check out then I'd start checking for some type of restriction. There's a short hose that feeds the water from the water pump in the lower unit to the adapter plate that the block is mounted on located at the bottom port side of the block. Item 12 in the diagram below. Make sure the hose is in good condition and nothing restricting the passage in the adapter plate which feeds the water to the block. Sometimes a piece of impeller blade breaks off and gets stuck and restricts water flow.

The water exits the block into the exhaust via the hose item 11 in the diagram. This water should be the hottest. If you can measure the water temp. exiting the block, it might tell you if your motor is really overheating.


http://www.boats.net/parts/search/Merc2/Force/120%20H.P.%20%281990%20L-DRIVE%29/120LD90B/EXHAUST%20SYSTEM/parts.html

 

[bustedbayliner]

Re: 1990 Mercury Force l-drive overheating

I checked the thermostat and also put a new one in it.Both of them opened up about 132 degrees. I do beleive there is some kind of restriction as well. We will be pulling off the hoses and checking them ,also we wil check the timing once more to make sure nothing got knocked outta place.Thank you so much for info. and feedback. If you have anything else let me know.
I will be posting more about what we find out.

 

[TYLER HUNN]

Re: 1990 Mercury Force l-drive overheating

the impellar on my 90 hp l drive basically crumbled when i took it out and i didnt find all the pieces. so its possible something is in your lines. wow you did alot of work to this thing. good luck finding out what the issue is.