Today we took apart the exhaust riser to inspect them before the Boating season of any rust. They are the typical inboard outboard MerCruiser risers on a PCM engine
You are the man.great explanation,we’ll spoken.car gear head just getting into boating and this is the best explanation I could find.thank you sir,subscribed!!!
Excellent! Thank you!👍 I just brought home a 2002 Wellcraft Excalibur 26' w/Mercruiser 496 HO Bravo. 233 hours. In addition to checking the raw water impeller, heat exchanger, will check risers.🤔 I'm learning so much, so thanks again! 👌
Hey there! Thank you for the video! Tell your deeply respected wife, sorry, but she wrong! Me, and my brother have some issues, so we find your video very useful. You could even show the scales, dirt, debries from closer to the camera, also your method as you clean it of. Keep it up, and thank you again!
This is five years after this was posted. Hopefully you’re rid of the wife now! If, today, you’re still tolerating that “thing,” get rid of her! Good job on the review. Nicely done and much appreciated! Again, get rid of her!!!
You forgot to add.. While you're in there, remove the exhaust elbows and inspect the water shutters, or flappers inside the top of the Y pipe. Buddy of mine hydrolocked his 5.7 Merc from flapper failure and it was ugly, crushed crankshaft bearings ugly. And of course I thought mine should be ok, only 260 hours on the boat, then my OCD kicked in and forced me to inspected them the next day and found one flap torn 2/3's the way through. Dodged a bullet there for sure.
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
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.
Hello to you, Just got involved here on your video. Great stuff learned a lot here. Also a shout out to Bob Kelly on some wonderful comments that helped me out Thanks Kevin
Clearly doesn't explain the operation of the system..For those wanting to know about the restriction here is a brief Mercruiser explanation. If you have a raw water cooled boat...you look at your thermostat housing. Does it have 4 bibs (hose connections) or 6? The 4 bib systems are known as "cold water" manifolds. You have one large hose bringing water to the engine either from the Alpha drive or the Bravo engine mounted water pump. One large hose bringing water to the engine circulatory pump, and two hoses going to the bottom of the exhaust manifolds. In this system ALL of the water brought to the engine exits through the manifold and riser. The gasket to use is the FULL FLOW gasket with all four passages open. Mercruiser's "Warm Water" system has two extra bibs (6) on the thermostat housing. The two extra bibs have hoses that connect directly to the riser. This system uses the RESTRICTED gasket. The reason behind this is...Your boat, whether Alpha or Bravo flows more water than required to maintain the temperature of the engine. Assuming you have 160 degree thermostat (for the sake of this discussion) In the "cold water" system once the thermostat opens you have 160 degree heated water leaving engine mixing in the thermostat housing with an endless supply of 50 to 80 degree ocean or lake water which drops the overall water temperature before it enters the bottom of the exhaust manifold. If the temperature is too low condensation may form on the inside of the exhaust passages and trickle back into your engine through the exhaust valves (which is why it is never smart to extended idle your boat). To alleviate this risk, Mercruiser introduced the warm water system which siphons off a lot off this extra 50 to 80 degree water before it attempts to enter the engine and diverts it directly out of the risers (hence the extra bibs & hoses) thereby increasing the temperature of the water that enters the bottom of the manifold
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
You discussed the elbow gasket but you have the wrong one for your application from what I see. If you have a water hose going to the manifold and the elbow you need the restriction gaskets like you have. If you only have 1 hose going to the bottom of the manifold you need the full flow gaskets.
I've never seen those green gaskets. Maybe they got rid of them. You gotta use metal gaskets on any exhaust; even water cooled exhaust. I have a motor that did this and had water in oil, for a while. The compression has suffered greatly, but not totally. Can't get it to kick now. Lots of visible rust on outside. I'm mulling over whether to call the engine bad. I'm leaning towards yes. Does anyone know what exactly gets damaged with sludge oil? Bearings? Rings? Everything?
Definitely not stupid. Garden city turkey trot! Are you available to walk me through some basics? I’m on Long Island, just caught some smoke from under left manifold area on a 4.3L Mercruiser stern drive. Heats up only at idle and under 5mph. Fresh to saltwater boat first time this year. I’m new but I believe could be thermostat issue. Who knows when the last time manifolds we’re checked the previous owner was a nut. I can probably pull this off on my own but if you’re available I’m willing to pay for the help. My mechanic down in Seaford is too busy for repairs he’s winterizing now obviously, and I won’t have peace of mind until January when he looks at it :/
my engine is intermitten overheating and goes into overheating mode, dead slow only. then once cooled down she runs fine all day. i boat in fresh water.
One riser is 110-120F and the other is 130-140F but my engine temp is rock solid low. So when you say temps get higher do you mean the engine or just high exhaust items are not good? How hot is to hot on risers?
I just bought a 1987 Chris Craft 178 LTD with a v6 & 2bbl carb. We took it out for a test drive and after 10 to 15 minutes smelled rubber burning. Checked motor and it was overheating. The temp gauge was past 220. The engine was not getting any cooling water.. My question is could this have done any major harm to the engine or valves? And how can I check for any damage?
I have a 357 Magnum bravo v4 today while pulling skiers I noticed at idle the thermostat would go to like zero. Do you have any ideas why this is happening? Never over heats.
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.
Would a worn/bad riser cause a lot of steam/condensation come out of the exhaust? Like, a lot more than the other side? Stbd exhaust has much more noticeable "steam" coming out, than my port side. Thanks for any help
Thanks for the detailed explanation guy! in case of headers, my port side header got really hot yesterday, water was flowing through the exhaust, at idle at least, and after 15 mins of running the boat i noticed the header really hot, just the port side. Any suggestion on what to check first? thank you again
Great vid. Good info. It's been 2yrs. About time to replace em aye? I'm fighting a 7.4 riser/manifold replacement. 6 broke bolts in the block. What's your favorite extraction method?
Why would you restrict the flow? I don't understand what you were trying to say. When you opened up the slot under the gasket. What's the point of one or the other? Great video. Very helpful
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