Mercruiser 888 Exhaust Elbow Mystery

[ctanke]

Greetings
I have a 1972 Mercruiser 888 that is fabulous condition. Fresh water only boat. Two years ago we replaced the thermostat, cleaned and inspected the exhaust logs and elbows and mounted with new gaskets for routine/preventative maintenance. Also added a new water pump just because. We've had her out on the lake a dozen+ times or so since then - engine always performs beautifully and heats up to 140 to 145 degrees at idol, WOT, and every where in between. No complaints!

I noticed yesterday when we had it running on a hose for 15 minutes that both of the logs but just the starboard elbow felt hot as expected (hand test) but the port elbow was only "warm" ( meaning I could leave my hand on it indefinitely). This seems odd to me that the port log itself is "hot" but the elbow connected to it is simply warm. All the while showing 140 degrees on the stat.

What do you all think?

Thanks in advance,

 

[Scott Danforth]

I think you should pull the elbows and manifolds for inspection at the end of the season this year.

 

[alldodge]

running on a hose

A hose doesn't supply the same amount of water that the drive can suck in when in the water. Its normal for one side to be hotter then the other.

I don't think you have a problem

 

[Bondo]

Ayuh,.... I'm with AD,... They never ever run exactly the same,....

 

[ctanke]

Thanks for the comeback guys. A few more questions . . .
1. With the 888 octopus thermostat system will the manifolds work up to heat, then the thermostat open up, and then the risers work up to heat (140 degrees)?
2. If the boat is in the lake, would you expect both risers to be the same temperature then?
Thanks!

 

[alldodge]

Water is always going to the exhaust whether the thermostat is open or closed.

There will always be a difference in heat for the exhaust. Water flows the path of least resistance and the design of the cooling system causes more water to flow one side over the other. Being in the water will increase the amount of water, but temps will still differ some. Note a 10 degree difference is about all it takes from leaving your hand on to not being able to do it

 

[ctanke]

Thanks for the clarification AD!

So, should I expect the temperature of the risers to be about the same as the manifold temps once the engine is fully warmed up (all at 140 degrees)?

Also, once warmed up, how much of a temp variance (if it exist) between the risers should I be comfortable with (before assuming a problem)?

CT

 

[alldodge]

There will be spots a bit hotter and some cooler. The issue is just look for things above 170 lets say. If the water you boat in is cool then everything else except the block will be cooler, just the opposite if water is hotter. If you start to small burnt rubber, that's to hot. I you touch something and it instantly burns you, that's to hot

A boat your age it would be a good idea to do as Scott mentioned