Can I use this riser?

Can I use this riser or do I need a new one? What can you tell from the photos? Note one small area that looks thin. Is this normal? The engine is a Volvo Penta 3.0l GLP-C.

I took the riser out because of a blown hose between the thermostat housing and the engine circulation pump. So I suspected a restriction in the system. I found an impeller piece at the very end of the riser under the exchaust rubber hose.

Re: Can I use this riser?

I don't see any blockages in your pictures, and that is probably not your problem.
Bet the engine is running cooler than normal tool
Most likely, you have a plugged up bypass passage in your thermostat housing. Likely another piece of your old impeller.
Here is a picture that shows a cut-away view of the thermostat hsg. and the location of the bypass hole.

Re: Can I use this riser?

I took also the thermostat housing out and it is clean everywhere including the bypass hole accessible under the allen bolt. Tested thermostat too. Do you think the impeller piece I found between the riser and the exchaust rubber hose was not restricting the flow enough to blow up the hose? I am afraid you are right because water could flow from the rest of the riser perimeter. The engine was running at 150 and never overheated but the riser temperature alarm was coming on at WOT. I will have to put everything back on when I receive the gaskets and hose and test again.

Re: Can I use this riser?

Don,
What is the reason you say "bet the engine is running cooler"? Thinking about your comment, it is my understanding that if the bypass hole was clogged then the high water pressure would force the thermostat off its seat at all temperatures. Is that the reason for your comment or you are suspecting something else?

Re: Can I use this riser?

When that hole is plugged up, the temp usually runs around 100? ? depending on outside water temp.

Do you think the impeller piece I found between the riser and the exchaust rubber hose was not restricting the flow enough to blow up the hose?

Click to expand...

Doubt it, but try it and find out.

Re: Can I use this riser?

I had the chance to work on the boat today. I just tested the boat on the driveway with a garden water hose and it was working fine. The temperature now is 170 up from 150 that was before I remove the impeller piece from the riser. I have also a new thermostat. The infrared temperature gun showed 173 on cylinder head, 142 on the hose from the thermostat housing to the circulation pump, 74 on the hose from the thermostat housing to the manifold and 82 on the riser around the sensor area. I hooked up a pressure gauge at the thermostat housing and at 1000 rpm's shows about 5 psi without additional pressure building up with time passing. However the real test will be at the water at 3000 rpms and at WOT to check if excessive pressure still exists to blow up again the hose from the thermostat housing to the circulation pump.