Does this sound like a manifold going bad?-gctid379070

[Guest]

So I was out yesterday, boat was running fine through the harbor, temp steady @ 175 per usual. Got up on plane once I hit open ocean, runnning at 3400rpm and the temp climbed up to around 190 after a couple minutes. Noticed white smoke out back as well. Just changed the impeller, new risers, and the manifolds are only a year old. No water in the oil. I have a hunch one of these aftermarket manifolds is leaking, just wondering if these signs point to that in your exxperience!

[Guest]

White smoke tells me either you are crazy rich, or the heads or head gasket has given up. Unfortunatley an overheat condition will result in a head gasket/head failure, but 190 degrees is not overheated for these components (Cars run regularily at 195 all day long with the same stuff).

I don't think the exhaust manifolds will give you this symptom.

My suggestion is to do a compression test and go from there.

Chay

[Guest]

hmmm....it does seem to be running rich- as in it feels loaded up and chugging when traveling no-wake speed for a while, and clears up when I put it in neutral and rev it out.

A little back history, I had an episode of a dead cylinder, had a stuck valve and badly corroded valve seats, ended up replacing the heads along with risers. The mechanic never returned to do a final timing tuneup after the boat was back in the water--Maybe I'll see if they can tune it up before ripping off the risers and manis yet again!

[88fourwinns]

Is it really white smoke or is the exhaust steaming? 190 degrees and exhaust steaming (the exhaust water is so hot it shows steam out the back) would suggest to me a problem with raw water flow and/or the impeller. Running rich produces black smoke not white. It might be worth it to remove the plugs, and disable the ignition. Then crank the engine over and see if you are getting water out of the spark plug holes. This would point to leaks between the riser and manifolds. If you can, pick up an IR temp gun at Radio Shack and measure the temps of your thermostat housing, manifolds and risers. It is a great tool for troubleshooting overheats. If you really have white smoke it could be a headgasket, if you want to investigate that do a compression test. Before that though I'd call the mechanic, he did replace the heads, I'd tell him what happened and get him involved.

[Guest]

Good points there--it did seem to look like steam rather than smoke floating around the back as it immediately dissipated. I've been suspecting the raw water pump as I've had rust develop on the outside of it-as i said, just replaced impeller, old one was fine. So if I'm thinking corrrectly, improper water flow would cause the low cooling flow to boil, thus causing steam?

[Guest]

I would make sure that your raw water supply hose isn't kinked or blocked. It sounds like it's just not getting enough draw if life is good at lower speeds and you're getting warm/hot at cruising speed.

[88fourwinns]

In addition to those above points, if this boat is docked or slipped in salt water, you can get barnacles and other growth in the water intakes, and it can get to the point where it will cut off some water flow and you can overheat even if nothing else is wrong. I had this problem last year and I actually had to remove the water screen in the lower unit of my Cobra outdrive because barnacles were growing in there. After I cleaned it out it ran at 165 like it always did before.

[Guest]

I'm going to pull the sparkplugs and make sure there's no water intrusion first. To test the raw pump, can I just detach from thermostat housing and run it into a bucket? Not sure what the flow should be, really.

[Guest]

(I'm talking about the circulating pump mounted on the motor btw, don't know which name refers to which pump!)