Manifold and risers are hot to the touch.

Ok I have a new to me boat with a 1995 volvo penta 5.7gipmda. When I first started it two weeks ago it was pumping water fine and manifolds were a little hot. Some rusty water came out the exhaust on the first start up. but cleared up fairly quickly. I Was working on another problem from a different post and I was running the engine on muffs, I noticed more exhaust smoke coming from the back of the boat than usual. so I looked at the water ports on the outdrive and they didn't seem to be pumping as much water. I have run this boat half a dozen times in the last two weeks and the manifolds have not gotten this hot. I checked the thermostat it was a 165 and manually it was working (freed up not rusted) the temp gauge was reading 180. My question is do you think this is some sort of blockage or bad impeller or bad circulating pump or manifolds and risers? What should I check first? Thanks in advance.

Re: Manifold and risers are hot to the touch.

How old is the impeller? Volvo recommends they get replaced yearly.
If you boat in salt water, the elbows and manifolds are probably plugging up.

Re: Manifold and risers are hot to the touch.

I do not know how old the impeller is. I will replace it Tuesday when the local shop opens up. If I take off the elbows will it give me a good idea of what is going on inside?

Re: Manifold and risers are hot to the touch.

bluecollerboater said:

I do not know how old the impeller is. I will replace it Tuesday when the local shop opens up. If I take off the elbows will it give me a good idea of what is going on inside?

Click to expand...

Ayuh,.... You'll have a clear view of the ports, yes, 'n after cleanin' up the gasket surfaces, you'll know how bad or good they are...

I find a flat file handy for that, if you can get at 'em...

Don't forget, you'll need new gaskets,...

Re: Manifold and risers are hot to the touch.

Thanks Bond-O,
I am going to replace the impeller first because I have no idea how old it is. If that does not work I will be pulling both risers to see what is going on inside. The risers look brand new though even the brass plugs on it are still shiny, no oxidation and the orange sealant they use is still on them.

Re: Manifold and risers are hot to the touch.

Ok I replaced the impeller today and ran the boat for about a half hour at 1000-1050 rpm and it never got over 165-170 degrees. The old gasket was ripped but the old impeller looked fine. I guess ya never know. I can grab a heat gun from work. What temperature should risers and manifolds run at?

Re: Manifold and risers are hot to the touch.

If you have a 165? thermostat in it, then 165-170 on the gauge is fine.
A torn pump gasket can allow the pump to suck air if the tear was on the intake side of the pump.
I would say put it in the water for a real test. Depending on your water pressure and volume, on your hose could cause temp problems.

The raw water pump on your engine puts out a lot more volume than any garden hose can keep up with. Have hooked up hoses directly to the pump with the engine sitting on the shop floor, and a little rpm would flatten the garden hose.

Re: Manifold and risers are hot to the touch.

Thanks Don. I will get it in the water as soon as I can.

Re: Manifold and risers are hot to the touch.

If you have an IR temp gun, you can take readings that will help you decide if the problem is fixed.
Yours may be different but this is what I have gotten on my '88 OMC with a 160 'stat.
Intake manifold right under the thermo housing: 155-160. Gauge usually says 165. Other parts of the thermo housing are usually cooler.
Manifolds, top of the riser section (these are one piece OMC V6 manifolds, and the top riser portion is always the hottest)
idle speed in the water, 85-95*
Idle after coming off plane, 125-135*. That is the hottest they get. If yours are hotter, then you have to keep looking. BTW if its hot enough that you can't keep your hands on it then its likely more than 140*.
Take a look in the lower unit intake holes make sure nothing is plugging them, boats that are moored in salt water like mine can have barnacles growing in the water intakes. I regularly have to rod those out or else it does start to run hot.

Re: Manifold and risers are hot to the touch.

Thanks for the tips Lou C. I will check the temps and the intake port.

Re: Manifold and risers are hot to the touch.

So I was thinking ( which usually gets me in trouble). If I hooked up the hose to the nipple on the forward part of the manifold then went to the outdrive to see how much water was coming out it would let me know if there was a restriction or not. Does anybody see a problem with doing this. If they are not leaking it should be fine. Please let me know if this is a bad idea. Thanks in advance

Re: Manifold and risers are hot to the touch.

I don't think that would be a good test. Because there is really nothing to compare it too.
Has the boat been run in salt water? If so, I would recommend pulling the exhaust elbows and checking the water passages and outlet passages in the elbows.

One other question, which outdrive do you have?

Re: Manifold and risers are hot to the touch.

I have an SP-C duo prop outdrive. Don I know I have to pull the elbows. I am trying not to open anything I do not have to. I can already hear what you are going to say. So go ahead I need to hear it before I will get down to doing it. And yes it has been run in salt water.