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Suddenly my risers and manifolds are hot

B

Bluecollerboater

Contributing Member
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.
 
First of all, is it getting hot in your driveway while running it on muffs, or is the boat on the water?

If it gets hot wile running on muffs, then try with half a plastic drum or large pail under the outdrive and fill it with water until at least the cavitation plate is submerged, then start the engine and keep filling the drum with a hose while the engine is running. If it still gets hot the easiest thing to check is the raw water pump impeller. If OK, the you should check the circulation pump, manifolds and thermostat housing. If you are running the engine in salt water, perhaps yo just need new manifolds or just try boiling the existing ones.
 
I've never had a problem using the garden and muffs..... for either low speed operation, or when doing ignition TA at higher RPM for a short duration.
We're not loading the engine while using the muffs, so in essence, we're not producing the same engine heat that we'd otherwise see while in the water and running.

IMO, engine cooling demands never quite equal the actual sea water supply. Most sea water is exiting through the exhaust system.

I think that the trick is, to make sure that the muffs are correct for the drive, that they are securely attached, no kinks in the garden hose, and that the water supply is adequate.
If your muffs are correct and securely attached, and with good garden hose water flow, I'd be willing to bet that you have another issue.



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I do not know how old the impeller is so I will put a barrel under the outdrive and try it. It was on muffs. It's a new to me boat that I had some fuel issues with earlier. The muffs I have are wired tied to fit. So I will try a barreling see if that helps. The risers look brand new including the brass plugs on them, they are shiny with orange sealant still visible. If the barrel does not work I guess it's time to replace the impeller then pull a riser to see if I can figure out what's going on inside. Thanks for your help.
 
I don't know what type of drive you have, but mine has a hole on the bottom on the drive and the muffs don't work for me. I put some hoses together and I hook it up directly to the intake of the raw water pump when I troubleshoot issues in my drive way. Search my posts, I believe there's a picture of it still on here. I'll search my photos and post it if I find it.
 
The 1994 5.7 GI-PMDA DP-C is very similar to the 1995 5.7 GI-PMDA, whether SP-C or DP-C.
So yes, you do need to be plugging the lower unit water drain hole while using the garden hose and muffs.

The advantage with the muffs, is that they supply water under pressure, whereas with the barrel you'll be relying on suction only.

If you have not yet replace the sea water pump impeller, at the very least it needs to be inspected.
 
Got a new impeller from my buddy who had a spare(stores not open today) putting it in now. I will also plug those holes. Post back in a hour and let you all know. Thanks for the suggestions.
 
Ok. I changed the impeller and ran the boat for 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. So I can grab a heat gun from work. What temperature should the manifolds and risers run at?
 
I found a pic of the hose contraption I made. It costs about a total of 12 dollars at home depot to buy the parts. I put this on the intake side (obviously) of the raw water pump when I run my boat in the driveway.

hose.jpg
 
1stboat said:
I found a pic of the hose contraption I made. It costs about a total of 12 dollars at home depot to buy the parts. I put this on the intake side (obviously) of the raw water pump when I run my boat in the driveway.

View attachment 6901
Click to expand...
IMO, (and just a friendly suggestion here) the down side to doing this is that we end up circumventing a large portion of the sea water path, starting at the inlet, the pivot tube seal, the water neck fitting, and a few other areas that may pose a potential issue.
These issues won't raise their ugly heads if we feed the sea water pump directly.

Remember..... the water neck fitting comes up and out of the water while on plane.

If we're having trouble with the garden hose and muffs, something is not right.
Better to find it now, than later on while out on the water.

Your call!



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Other things to do are:

Drain the block - both sides. There may be muck in the bottom of the block.

Remove all the hoses and check for blockages.

Remove the manifolds and risers and check for rust - I had to replace mine when I got my new-to-me boat also.
 
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