4.3 running hot on one side

[13crazyhorse]

I have a 2002 trophy with a 4.3 mercruiser. Runs great and always did till now. Half way thru the summer I powered it up to get on plane and it overheated. Alarm went off temp 200+. Shut it down and went in on the kicker motor. Replaced the thermostat. Ran it a little still threatened to overheat so I changed the impeller. This made it better it wont overheat when powered up but still runs warmer than it should. Temp gauge reads 185. Correct thermostat installed is 160. One manifold and riser is considerably hotter than the other. I checked it with infrared temp gun and one side is around 125 while the other is 180 and up to 200 if you get close to the engine. Pulled off the manifold and riser and they are both pretty clean. No blockages or major rust. Any ideas on what to do next? Thanks for any input.

 

[Scott Danforth]

the hot side is not getting flow.

check again for blockages. both on the incoming side and the outgoing side.

 

[13crazyhorse]

Wouldn't it have to be somewhere between the thermostat and the exhaust exit? As the thermostat opens it feeds both manifolds?

 

[alldodge]

What is the motor serial number?
You have single, 3 or 7 point drain?
Assuming open cooling

 

[Howard Sterndrive]

One manifold and riser is considerably hotter than the other. I checked it with infrared temp gun and one side is around 125 while the other is 180 and up to 200 if you get close to the engine.

this is on the trailer? or running down the lake on plane?

any power issues?

 

[13crazyhorse]

Serial #M087992. Not sure what you mean on the 3or 7 pt drain. Correct in the open cooling. In response to Howard makes no difference if it on the trailer, in the marina or going down the lake on plane. No power issues at all everything else is fine.

 

[wahlejim]

You have blockage somewhere on the hot side. Y-pipe shutter may be melted and sticking, restricting water flow.

 

[13crazyhorse]

I have pulled off the manifold, riser and elbow. The shutters seem fine. I ran a hose down the y pipe and the water runs out of the bottom by the outdrive.

 

[alldodge]

Serial #M087992. Not sure what you mean on the 3or 7 pt drain. Correct in the open cooling. In response to Howard makes no difference if it on the trailer, in the marina or going down the lake on plane. No power issues at all everything else is fine.

Not knowing the serial number it could have had one of Mercs "special" drain systems, yours doesn't so all good.

Your cooling system is pretty simple, so if the thermostat, hose, connector, mans, elbows and have used the correct gaskets then it should not happen.

This is Bravo drive



Suggest getting a 1 inch ID piece of clear hose about 6 to 8 inch long from the hardware store, a double barbed fitting, and couple hose clamps. Install the clear hose between the thermostat housing and the water hose coming from the drive. Then run and look for bubbles

 

[13crazyhorse]

It has the alpha 1 gen 2 outdrive. Im gonna pull the thermostat housing off tomorrow and have another look at it. Maybe I'll try it without the thermostat installed. I'll put the manifold and riser back on with new gaskets since they look fine.

 

[alldodge]

Your boat, but a piece of clear tubing cost $2 a foot at Lowes, a barbed fitting about $4, couple clamps cheap. Can also use 1 inch pvc pipe and not barbed fitting, not much pressure. You will know if there is a air leak, which can then look to the drive, or not if no air leak

 

[13crazyhorse]

You are right alldodge. I will try that first tomorrow. I'll post the results when Im done. Thanks for the help.

 

[Rick Stephens]

Any possibility your raw water pump is not supplying enough flow?

 

[13crazyhorse]

OK heres the latest development. Went to Lowes and got the clear 1 inch pipe. Turns out the fitting is 1 1/2 inch. My fault should have looked first. Anyway I put everything back together and to no surprise no difference. When is was cold I started up the engine with the hose off that goes to the side I'm having trouble with. There is water flow but its sporadic not a real steady flow like it should be? Also when everything is hooked up and running I noticed the cool side has lots of water coming out of the outdrive and the hot side is mostly exhaust. Guess my next move would be removing the lower unit and checking everything on the new impeller? Maybe the tube that goes up didn't seat properly? Thanks for your help so far.

 

[alldodge]

1.5 ID woops my bad

 

[13crazyhorse]

Ha, ha no problem alldodge! I appreciate the input. Hope I'm on the right track now. Will drain the outdrive and have a look at things inside there this weekend.

 

[Rick Stephens]

Also when everything is hooked up and running I noticed the cool side has lots of water coming out of the outdrive and the hot side is mostly exhaust.

Are you noting how much water is coming out of the water relief ports to each side of the transom/gimbal housing, and that is what mean by more water out of the cool side? If so, then that has no bearing on anything as the exhaust with water goes through the transom in one passageway before splitting off to the two idle relief ports. How much water comes out of each is totally up to the water gods.

Guess my next move would be removing the lower unit and checking everything on the new impeller? Maybe the tube that goes up didn't seat properly? Thanks for your help so far.

Pull the drive, then just take a cutoff piece of 3/4 garden hose and shove into the bellhousing water passageway - where the o-ring is. Crank the water on and fire up. You will have full hose supply to the thermostat as long as there is nothing plugged in the oil cooler.

BTW, even before doing the above, I would pull the line off the thermostat housing that comes up the port side from the transom - the water supply line. Leave it hang. Turn on water, fire off motor and LOOK at how much water is coming out. That'll tell you right there if you are getting good flow from the raw water pump.

Rick

 

[Lou C]

I would not pull the drive off yet. I would put the boat in the water and do Mercruiser's test for raw water pump output. That will tell you what you need to know under actual operational conditions. If that is good then move on to the thermostat housing...that is what splits the raw water flow to each exhaust manifold on a V engine. You may have a blockage inside the t-stat housing on the side that feeds the hot manifold.

 

[13crazyhorse]

I realize the exhaust y pipe does not separate the exhaust and water but as the water goes down it it tends to cohere to the side of the pipe that its on thus going out that same side on the transom. If you run a hose down the port side it comes out on the post side and vice versa. Also as I mentioned earlier I have changed the thermostat so the housing was inspected and there were no blockages in there. I also changed the impeller so I'm leaning in that direction perhaps I did something wrong. Not a big deal to go over that work checking o rings etc. The whole system is very clean cause boat is low hours and always fresh water. I'll post my findings. Thanks.

 

[13crazyhorse]

Ok now im thoroughly confused. I went out this morning and figured I would play around before pulling the outdrive. I backflushed with a hose again to the outdrive. Water comes out the outdrive. I hooked up the hose started it up and removed the incoming hose from the transom. Seems to be good water inflow. Took off the hoses one at a time to each manifold. Decent water to both sides. Problem is now the other manifold is overheating not the original one. Maybe there is something going on in the thermostat housing? When it cools I"ll have another look. Wow.