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waltzal

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"I have twin raw water cooled

"I have twin raw water cooled 5.7 Merc's. They are 5 years old, but only have 140 hours on the engines. I just noticed that my one engine has warm to hot risers. The engines runs well and my temp guage shows normal. The other engine's risers are cool. What is the problem?"
 
raw water continuosly pumps th

raw water continuosly pumps through risers as soon as it is started the block doesnt get any water flow until thermostat opens. when is the last time you have serviced the water pumps ?does riser cool down if u raise rpms? could be plugged and not getting out.
 
also is there a hose 3/4in go

also is there a hose 3/4in going to riser? if so remove start engine check flow. if no hose manifolds could be plugged
 
Water pumps were replaced a fe

Water pumps were replaced a few months ago. How do you know when your risers/manifold go?
 
"They start getting hot.... ne

"They start getting hot.... next step in the degradation process is they'll allow raw water into the cylinders when you shut the engine(s) off.
What happens is the metal inside the cooling passages starts to corrode and flake off in chunks. Small chunks are no sweat, they just get flushed out with the water and exhaust. Big chunks get stuck and restrict water flow. Which leads to higher temps, which leads to more rapid corrosion, which leads to more chunks... etc, etc. Eventually the walls between the water passages and the exhaust passages are corroded away.
A lot of folks will tell you risers (and manifolds in raw water cooled engines) are 4-5 year consumable items. If you run in fresh water, you'll get by longer, seawater... 5 years max."
 
"For both engines... get some

"For both engines... get some financing.
Doing the work yourself, you can probably plan on spending about $800 per engine. If you look around, sometimes on ebay, you can find them a little cheaper."
 
"Haven't bitched about thi

"Haven't bitched about this for a while, so...

Buy a laser pointed non-contact thermometer and see what's actually going on. Not only will you no longer be guessing, you will see WHERE the heat pattern is do you can fix it.

Jeff"
 
"Walt,
I'm with Jeff. Fi

"Walt,
I'm with Jeff. Find out what you have before you go into panic mode. You haven't mentioned if you are fresh water or salt. This has a big effect on manifold/riser life. Routine maintenance also has a great effect on life. Have you ever removed and cleaned or inspected the risers? It sounds like it's past time. If you don't feel up to it, pay someone who is. Five years is a long time, even if you only have 140 hrs. on it. You may find that you simply have a buildup of salt or scale which can be removed. You may find that with a little effort and $50.00 worth of gaskets, you're good for a few more years.
Good luck, Rick"
 
"I've been thinking about

"I've been thinking about this. Like Rick said, since both sets of manifolds and risers are suspect, based on age, I would pull them off, clean them up and inspect them. Use a small dental mirror ($3 at a flea market) and a flashlight to look inside the accessible passages. If I could convince myself that I had one good set, that would last 2-3 years, I would install that set and replace the other. This would at least set up a staggered roatation so that when it came time to replace them, I'd only have one engine's worth of gear to pay for at a time. This of coarse assumes one set is salvagible and there's not something else wrong.
I think we all agree, left unattended, this problem, in time, will go from a curiousity to a catastrophy.
FASTJEFF's recommendation regarding the infrared thermometer is right on... a must have for inboard engineers."
 
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