exhaust manifold temp question

[jmr12]

2003 VP 5.0 MPI Duo Prop. Purchased March of 2010
I had a mechanic winterize the boat and he said that it looked like the raw water impeller has never been changed, I agreed and changed it. The new one looked exactly like the old/original one.
When I start the boat in the water, drive all the way down, It seems like it takes a long time for the water to start to cool the exhaust manifolds. I start the engine in neutral and rev, go to the back of the boat and put my hand on the manifolds. They heat up quite fast, 30 to 60 seconds. I put the boat in gear and give it the gas to bring up RPM and get the water to circulate as quick as I can. Check manifolds and they are cool to the touch.
Am I getting too nervous about this? Am I giving the pump enough time? How hot is too hot for the manifolds before they start to melt stuff? The manifolds do have sensors on them. I asume that if they get too hot it will shut down.
I have always been one to let an engine warm up before working it.
Thanks

 

[Don S]

Re: exhaust manifold temp question

Sounds like you may have a small air leak on the intake side of your raw water pump. When you first start it at low rpm, all you are doing is sucking air until you speed it up and get some water to it.
Did you replace the oring on the pump? If it ran dry for any length of time, it may have damaged your new impeller. Would be worth looking at.
Another place to look is the flush hose on the engine. Make sure it's tight. That is another good place to suck air.

 

[jmr12]

Re: exhaust manifold temp question

Thanks Don.
I did replace the oring. Put some lube on the impeller and the oring when I replaced them. Everything went back together very well. All the hoses look good. It seems like after it gets primed it is o.k. I thought that maybe I am not being patient enough. How long do you think it should take to get water to the manifolds? Will they get hot before they fill with water?
I will check again for week hoses, and the engine flush hose.