Bad riser

[skeffer]

How can you tell if a riser is bad. I have a 470 mercruiser 1978 it seems to run a little warm when running above 15mph has new impeller. someone suggested that the riser may be bad.

 

[steve n carol]

Re: Bad riser

Sid, you can pressure either the water jacket or the inner exhaust area. I fashioned a plate to cover the square area, (where it mounts to the manifold), then used a "dollar plug", a cheap expandable plumbers tool, to block the 3" round exhaust opening. In the plate I installed a fitting like on an inner tube in which I injected compressed air. Submerged this into a bucket of water and ta-da, instant $$$! (to the parts store).<br />The log manifolds were eaiser to test, about 20 psi should do it. I checked those in a wheelbarrow full of water. You could probably check them together...sl

 

[steve n carol]

Re: Bad riser

Sid, Running warm...this could be a result of a lot of other problems. do some 'serches' on this site and read what others are experiencing. Myself, I found a piece of plastic tubing in the supply hose comming in from the outdrive. Still can't figure out where it came from. This piece was partialy blocking the system and causing overheating...sl

 

[skeffer]

Re: Bad riser

S & C I know I have been following several warm issues and post. I have replace the impleer and was wondering idf a piece got pushed up the supply line which I am getting ready to check. It does act like a restriction as it is fine at lower speeds.someone suggested that the riser may be bad so I was wondering about that getting it off is a pain on my boat. It is a 78 silverline and not much room over the engine it seems. It acts as tho the water is not circulating enough at higer rpm/mph to keep it cool. I replaced the water imp last week and it was shot and missing some rubber. I did find what I thought was all of it no I am not sure. I do have water flow from the prop exhaust just seem to me like a low volume amount tho.<br />

 

[Blk-n-Blu]

Re: Bad riser

skef, Here are some tips on diagnosing an overheat problem:<br /> http://www.marinemechanic.com/site/page85.html <br />Hope it helps<br />Also check the engine circulating pump. The impeller on that pump may be gone.

 

[steve n carol]

Re: Bad riser

Skeffer, search "water pocket" and "clear tubing", achris explained this quite well. <br /><br />After warming to operating temps (which I thought was HOT) I opened various petcocks while the engine was running and took temperature readings on the hot water streaming out w/a thermometer. after that is when i found the trash in the supply line. I have pet cocks on each riser, each manifold and a couple on the block. I read on this site that risers can become plugged at the place where water is introduced into the exhaust, (with soot and silt,rust,barnicles and other small anamals etc.) The pet cocks on mine are right at that point (so as to drain them). So, after warm up the water will start to folw through the riser and out the back (somewhere), at that time you can check the water temps and verify your gauge and calm your fears, maybe...sl