Thank you. You can clean the surfaces by lightly scraping it and lightly sanding it with sandpaper on a block of wood to keep it flat and even

Great point! 100% right I just inspected mine after a minor hydrolock. There was nothing left to them. I'll probably do a video of them next time I inspect risers. Thank you

Capt n B garage Make sure to get OEM not Sierra, they're junk.. Falling apart after 4 easy years.. Is it just me or is Everything garbage these days.

This is the reason Volvo Penta removed flappers years ago. They had more issues with them falling apart and laying the bottom, blocking exhaust and causing issues...now for boats low in the water it puts the water to close to the exhaust ports some people put in taller risers to solve any concerns.

+Bob Kelley thank you

Is it ok for my risers to be very hot to the touch before the thetmostat opens to cool them down ? Idk whats going on with my boat i have the 1984 228 305 V8 5.0 motor thats been getting super hot during idle and trolling speeds but i pulled lower unit to check impeller but its just fine looks new, which toom me to the thermostat i pulled out old one replaced it with gasket and sleeve , fired her up and the risers were super hot to the touch but this was like 4 minutes of it idling on muffs, if you could help that would be wonderful thanks.

I am guessing you have an Alpha drive because you pulled the leg to get to the impeller. (Bravo's have engine mounted pumps) but is your engine raw water cooled or fresh water cooled? I'm assuming it's raw water cooled.....It does not matter whether the thermostat is open or not when we talk about water cooling your exhaust. The water is brought in by your impeller, which flows way more water than the engine needs, to the themostat housing. Which has either 4 bibs (cold water) or 6 bibs (warm water). On the cold system your 4 bibs are....intake from pump to thermostat housing.....housing to circulatory pump....housing to bottom of port manifold...housing to bottom of starboard manifold. Whether the thermostat is open or closed...the water comes into housing and goes out the manifolds. Period. The thermostat has zero effect. It only controls how much of that water gets fed through the engine by the circulatory pump. The warm water system adds two bibs and two hoses. These two hoses go from the housing to the risers. When the water flow is high (rpm), or thermostat is closed and no water going through engine they help bleed off excess water to keep the water entering manifolds at a higher temperature to avoid condensation. Therefore if your risers are truly hot (define hot?.. A good tool for a boat owner is to buy an infrared thermometer at Harbor Freight...theyre cheap and work great)... Therefore...to reach a conclusion we must ask........does your engine run hot? How old are you manifolds and risers? Before 2002 Mercruiser used "wet joint" risers. Their lifespan (in salt) is about 5 years for risers and maybe 7 for manifolds though most change both at 5 years due to labor. They usually fail first at the gasket but a sign that you manifolds and risers are starting to go is you start running hotter. If you're boat has 160 thermostat, is raw water cooled and ingesting endless supplies of 70 degree outside water it should not run hot...unless...the intakes in the drive are blocked with barnacles etc restricting the water to the pump....the pump is not pumping the water....I can't count the number of people who have told me impeller was good when it wasn't.....the hose from the drive to the engine is blocked (corrosion in the transom housing sometimes restricts the hose)...the hose from the transom to the thermostat is kinked...the manifold and risers themselves are blocked with rust and scale...or one of the flappers in the Y pipe (assuming your boat has them) has fallen off and is restricting the exhaust. Those are you possibilities

Bob Kelley hey thank you so much for the reply ! Ok , now since I type that I went home took off the lower unit part where the impeller is took off the housing and I seen the impeller lost two fins both top and bottom housings were melted when I took the outdrive off last time the impeller looked good it wasnt missing any fin (veins) buy i also didnt remove the impelller from the housing the first time either, so thats what was causing my mainfolds to get super hot , no water was circlating much, today i went and bought new everything top housing and base housing, now am i screwed that the fins that were missing are gonna make my boat overheat now ? Or am i going to be ok, i know theres water getting to the motor but not like it should have been, my risers were hands on for 6 seconds and i couldnt hold them in any longer it got so hot.

Corey Couch of course you’re screwed but that’s the fun of owning a boat! What you have to do is clean the system. Pull the hoses off and make sure they’re clean. Most likely the pieces are in your thermostat housing. The power steering cooler etc I knew your pump was bad. If I had a quarter for everyone who started with “my impeller is good” I’d be rich

Gotcha, and how do I know if mine is designed to be blocked or not? After watching this video, makes it not seem to hard at all. I'm wondering if I pull off riser , would gasket not be reusable for remainder of season? Thanks

It could if your not getting enough flow. I would check your outdrive water pump. If that's worn and you didn't get enough flow it would steam

If you remove the risers you can see the exhaust manifolds water jackets

Check connection at the thermostat housing. Should be a Brown wire or a brown w/blue

Yes. Close the water inlet valve and proceed with repairs. If it doesn’t have a valve at the water inlet, no problem. Raw water (salt water/lake water/river water, etc.) will not get to the risers and exhaust manifolds unless the water pump is running; the water pump only runs when the engine is running.