How to check risers

badrano

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Aug 7, 2018
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I'm trying to get a baseline on the condition of the manifold and risers. During the boat survey, the riser temps were about 10 degs above nominal range. I'm pretty sure the manifolds and risers are the original since the majority of the bolts are painted black.
Is there any way to check the water passages for blockages without having to remove them? Is it possible to remove the coupling boots between the riser and the Y pipe?

If I have to pop the risers off, can I re-use the bolts? I know the gaskets would need to be replaced.

The boat was a fresh water boat and I now operate in brackish to salt water but I flush when I get home. I know freshwater boats are not immune but more immune than salt water boats.
 

alldodge

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You can reuse the bolts

The slight temp increase may just need the impeller changed, could also be the lake water temp. If the lake temp goes up so will the temp on the risers

What does the survey say the temp should be?
 

Bondo

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If I have to pop the risers off, can I re-use the bolts? I know the gaskets would need to be replaced.

Ayuh,..... The bolts can be cleaned up, 'n reused, so long as they're not rusted away,......

I use only the graphite/ metallic gaskets, not the green paper ones,....

What yer lookin' for is a solid 1/4" of iron, 'tween the water ports, 'n the exhaust port,.....
 

badrano

Petty Officer 1st Class
Joined
Aug 7, 2018
Messages
331
You can reuse the bolts

The slight temp increase may just need the impeller changed, could also be the lake water temp. If the lake temp goes up so will the temp on the risers

What does the survey say the temp should be?

Based on the survey, the nominal range is 150-165 and his readings were 155-185. Impeller was changed right after we bought it near the end of the season. I'm not having any over heat issues. Maybe I need to get one of those temp guns. Not sure if it's worth the money for new gaskets just to pull the risers to see if there is any rust build up.
 

alldodge

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If the boat has been in fresh water only, there would normally not be any issues with them. I have a 25 year old set remove from my boat sitting in the shop and other then some surface rust there as good as new
 

Lou C

Supreme Mariner
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Nov 10, 2002
Messages
11,802
Does this boat use the Merc warm
manifolds set up? Because higher temps may be somewhat normal, at about the same temp as the cyl heads and engine block warm because the manifolds do not get cooling water till the thermostat opens up while the elbows get cooling water all the time. So it also depends on where he is taking the readings and if the thermostat is open or not. My OMC and all Volvo’s I have ever seen have cold manifolds and run substantially cooler. With the original OMC batwing one piece units the hottest they got was about 135 after coming off plane and then cooled down to about 100 after idling about 5 min. Since I switched over to the later style center riser system used later on by OMC and Volvo they run even cooler topping out at about 110 after coming off plane. At idle they are usually at 85-90. I think Mercs idea was to keep the manifolds hotter to prevent condensation after running at low speeds. If you are in salt water now figure on a 5-7 year replacement schedule if you want to avoid problems. I did this over the 17 years I’ve had this boat (all salt moored 6 months each season and not flushed till the end) and had 3 sets of bat wings and this new set of center riser exhaust I installed a couple of years ago. Never had water in the cyls from defective exhaust but as you can imagine it gets expensive unless you can do it yourself
 
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