Stbd Riser hotter than Port

[jeffreyh75]

Scenario: 5.7 EFI Merc seawater cooled, while underway comparing the STBD riser to the Port riser shows a signifigant difference in temperature. The STBD side is almost too hot to keep your hand on it, while the port side is much cooler - just warm.

I have done countless research and talked to many mechanics. Some say that the hotter riser is plugged, etc. After disassembling it twice and checking it thoroughly, there is no sign of plugging, corrosion or other obstruction. It is a relatively new riser and I cleaned it out so I know this isn't the problem.

I called Merc and they said that this is common as the way this engine's seawater cooling is routed, it goes through the STBD side first, then the port, and it is normal for the risers to be different in temp.

No apparent overheating problem now (after clearing nasty barnacles from the intakes on the outdrive) and temp is pretty much normal at 172.

Any ideas and do you agree that this could be normal?

Thanks!

Jeff Herzog in NJ - counting the days down until spring!

 

[nauticaldog]

That's not normal. I had the same problem when I bought my last boat. Luckily we caught it during the survey. It wasn't the riser that was plugged, it was the manifold. How old are your manifolds? You may be due for replacement.

 

[Air O'Nautical]

If you cant hold your hand on it RUNNING, its too hot.
There isnt enough water running through to cool it. I agree with the manifold change. Raw water, every 5ish years new manifolds and risers. Its an expensive wear item.

 

[jeffreyh75]

The risers/manifolds are about 3 years old - salt water. I took off the manifold when I checked the riser and it was clear and clean. Hmmmm....

 

[H2ONUT]

Plugged mainfold. On mine, the STBD elbow was too hot to touch, same as yours. It was the PORT manifold that was blocked.

CSR member Playdate was very helpfull in working with me resolve this issue. If you do a search, you should be able to find the thread that was started by me.

 

[Air O'Nautical]

HHmmmmm....
Any hoses kinked or blocked?
Riser gaskets correct? Some have four slots and some have two slots and two holes for the water to flo thru..

 

[2007Amberjack]

I went through this last season with my old Bayliner 2452 with a raw water cooled 5.0 Merc with alpha 1.

I changed the manifolds, risers, elbows, ect! $1500 in parts.

The starboard side was always 30-40 degrees hotter thant port side due to the way the water is routed through the engine. The cooling water would go through the block first then route into the manifolds and then up into your elbows.

It is normal just watch you temp gage.

 

[Chris Dauth]

Inside the tee piece on top of the thermostat housing, there are 2 spring loaded plastic balls that are to send equal quantities of cooling water to the port and starboard manifolds. They get stuck. Just take off the hoses and check them out

 

[greenstreak]

I have had this same issue with my merc 7.4 mpi It was overheating after I had an annual done. The engine was overheating. i have changed thermostat, temp sending unit, checked the elbows and risers. they are only 2 years old and used very little. Impeller was changed but the mechanic did not changed the plastic housing. I was told that it should have been changed with the impeller becaused they will get grooves in them. So I had a shop to change the housing. It is running cooler now. I have been told by several mercruiser mechanics that is is normal for the elbows to be a different temperature. Also I was told it is normal the elbows to be 200 degrees while cruising. My temperature gauge is aroun d 185 now. They said the big blocks will run much hotter then the small blocks. also the elbow temperature can change from one side to the other. Just depends on how it is coming out of the thermostat housing.

art

 

[greenstreak]

2007amberjack---Have you ever shot your elbows on your 6.2L with an ir gun while on cruise? if so, what temp did you get on top where the exhaust is flowing? I shot mine and got 205 and this is suppose to be normal with big blocks.

art

 

[Paulie Walnuts]

Hi.
Paulie Walnuts here...

I'm having similar issues with my 1986 5.7.
It's a brand new motor, but used manifolds and risers. The impeller is new. When I first took it out, I was getting a high RPM over heat at full throttle. Then it would quickly cool down when I slowed down.

My Mechanic recommended a new type water neck that eliminated the hoses to the risers. After switching that out along with the old risers gaskets to the new 4 slotted type. The motor does run much cooler, and doesn't over heat. But now my risers are hot to the touch, and I could feel that the left side riser was hotter than the right.

So I went out and got an IR Temp gauge and these are my results. (Granted this is running off a garden hose)

Temp gauge said: 160
The Laser said the block was: 145
I have a 140 thermostat.

L manifold: 136
R manifold: 111

L riser: 138
R riser: 114

L exhaust boot: 122
R exhaust boot: 115

Averaging about a 20 degree difference from the left side to the right side.

So is the 20 degree difference normal for a 5.7 Mercruiser? (Pic below)

If the weather permitts, I plan on takeing it out for more tests on the water this weekend.

Paulie :huh:

 

[comsnark]

I last did temps on my 5.7's two years ago. Risers varied about 20F. 120-140 rangeish.

Personally. . . I don't put my hands on parts that "may" be too hot to touch. Especially on a running engine. Especially with the boat running somewhere between cruise and W.O.T, and the water ain't glass!. I use an IR gun so I have a more quantitative benchmark. I have seen 195 (gulp) on my risers. . .with the temp gauge up front at 200+ (gulp).

Actually. . .I never did temps at W.O.T. because (1) I never got "glass" to run on when doing this - not exactly stable back there! and (2) The engine hatch acts too much like a drag chute for my tastes once the boat is moving over 40mph.

 

[thomas]

My exhaust is so hot on my 1981 7.4 that it has blown a hole the exhaust hose on the port side. Have taken off the manifold and riser, and they both look good. The gasket on the manifold was shot, but other that that is was fine. I have also checked the thermostat and check valve. All looks good and in working condition.
This all started when I ran in to some sand/silt last year.
What am I missing?

 

[comsnark]

Hi.

So I went out and got an IR Temp gauge and these are my results. (Granted this is running off a garden hose)

Temp gauge said: 160
The Laser said the block was: 145
I have a 140 thermostat.

Sounds like you need to swap out a thermocouple. . .a few degress off is fine. 25 is not fine.

You have a 140 thermostat? Interesting. I have a 160.

BTW: I am not sure how much you can tell running off a garden hose. IIRC, a hose will get you about 2-4 gpm. IIRC, the motor is going to want twice that amount at higher RPMS. It may give you SOME information. . .but I wouldn't trust it.

A few years back, when my mechanic was scratching his head, we put the out drive into a 55 gallon drum full of water to run-test the motor. This allowed the motor to suck up all the water it wanted. He didn't do this for long. . as you are recycling crap water back into the engine. . .plus the water is going to heat up. . .but for a serious check out with a bit more water than a garden hose can supply. . . something to think about.