Mariner overheating

LuvToFish50

Recruit
Joined
Jan 26, 2004
Messages
2
I have recently purchased boat with a 1986 Mariner, 135 HP engine. The motor had a bad cylinder when I got it so we had that cylinder bored for an oversize piston, and had the other cylinders honed. New piston and rings for the bad cylinder, and new rings for the other cylinders. We checked the waterpump and the impellor was off the shaft. It looked like it had split and just came off without loosing any pieces so we figured we might have found the reason why the motor had lost the cylinder in the first place so we changed it along with the complete pump housing and all. When we cranked the motor on the hose it didn't have much of a stream coming out and ran hot pretty quickly. Next step was changing the thermostats (which were really corroded). We ran the motor on the hose again and the overheating problem seemed to be better, but not much improvement on the stream. We decided that maybe it would be better at a little higher RPM so we took it to the river. It ran fine at idle (as smooth as any outboard I've ever owned) but when we brought it up on plane it ran the alarm went off and the gage was pegged within a quarter mile. The stream still didn't do too well even with the higher RPM's so we checked the poppet valve and it was in pretty bad shape, with a lot of corrosion and a tear in the diaphram so we got a kit and replaced the whole thing. This really made a difference in the stream while on the hose so we took it back to the river and it ran great at idle but overheated again in about the same distance. Being out of daylight we took the boat back home and the next time out we took the new thermostats out and tried it without them. This time everything looked great again and it did fine at idle and low RPM's but when we got up to speed it pegged the gage again. The only difference is that the horn didn't go off this time. We tried it several difference times all with the same results. I don't know why the alarm isn't sounding but the gage is definatly pegging out. We moved the timing on the high end both advanced and retarding it with no difference. Being still in the breakin period, I haven't been able to run the boat above 3000 RPM but it runs hot while at that speed. The motor has 4 to 6 pounds of water pressure at idle and about 22 pounds at 3000 RPM's. We are using the oil mix from the motor and mixing the oil in the gas as well to make it double oiling for break-in which makes the motor smoke really bad. I'm at a total loss and don't know what to try next. If anyone could offer any suggestions it would be greatly appreciated.
 

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: Mariner overheating

Is this motor run in saltwater? Only thing I can think of at this point is corrosion in the water jackets. Other Merc./Mariner guys with more info will chime in...
 

mellowyellow

Vice Admiral
Joined
Jun 8, 2002
Messages
5,327
Re: Mariner overheating

have you checked for blockages in cooling system?<br />manually mixing oil/gas or is it auto?
 

LuvToFish50

Recruit
Joined
Jan 26, 2004
Messages
2
Re: Mariner overheating

This boat is run in salt water, and I forgot to mention that we removed the waterjackets on the heads and checked for blockage. We even put a hose in the holes where the t-stats were and made sure that water came out of the bottom when we had the lower unit off to change the water pump. <br />We are using the automatic oiling and manually mixing oil in the gas as well. <br />I think I'm going to buy a new gage and sending unit to check them out, but I just hate throwing parts at a problem.
 

mellowyellow

Vice Admiral
Joined
Jun 8, 2002
Messages
5,327
Re: Mariner overheating

try a melt stick b4 u buy new gauge.<br />running lean will heat her up quick, so look<br />closely at carbs as well.<br />good luck,<br />M.Y.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Mariner overheating

Try reducing the spring pressure on the poppet. Cut one or two rounds off and test. The worst that can happen is you need a new spring.<br /><br />Good luck!
 
Top