Exhaust Manifold too hot to touch

ConchPirate

Seaman
Joined
Jul 20, 2011
Messages
52
Sounds like you have twin engines. Mine is in the shop right now to have them check/replace the water tube from the lower unit to the gearbox due to an overheating issue of manifolds/risers on my port engine at idle. Installed brand new Volvo pump, thermostat and housing like you did. Different than your problem per se, but what I did to determine if there was a supply line issue (air/cracked plastic fitting/bad hose, etc.) was to install some clear tubing that would allow me to draw water from the opposite engine. Since my issue was on the port manifold/risers at idle, I connected a line from the starboard intake line to the port pump. Engine ran fine and manifolds never got above 120F. Then hooked up the port side supply line to the starboard engine and it ran perfectly (and was never an issue). This proved it was not a port side supply line volume or air issue but rather only when the port engine exhaust was influencing the water pickup. So if you have the hose try using the opposite engines supply to determine if it is a supply side issue or post thermostat housing/manifold or riser issue.
 

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MI CC

Cadet
Joined
Apr 15, 2019
Messages
17
Didn't have long enough tubing to connect directly from thermostat housing to opposite engine impeller housing. Connected from opposite engine thermostat housing to manifold and the same riser still got a lot hotter at idle than other three risers. Exhaust manifold stays cool however. Although the engine temp of the engine that the riser is getting hot never overheats or gets above 175, it does heat up to 175 quickly whereas the other engine takes 3 times as long to heat up to 175.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
Did you ever look to see if there was a melted flapper in the bottom of the Y pipe on that side? I think Volvo quit installing them in '99 so your '98 could have had them, even if someone removed them they might not have thought to check.
I'd be tempted to pull the drive with the elbow off and really take a good look in that Y pipe and the exhaust opening in the transom mount. Running out of ideas at this point!
 

MI CC

Cadet
Joined
Apr 15, 2019
Messages
17
Lou, yes I had looked down the y-pipe and there wasn't a flapper or holes where a flapper might have been connected. Boats coming out for the season in a couple weeks so just going to have the marina look at the drive.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
PS
I just bought a spare Cobra outdrive off of ebay, in very good shape, and found a melted flapper jammed in the area where water flows from the transom mount into the drive, to exit the prop, it was stuck between the shifter rod and the side of the drive, so you never know where they can wind up....
 
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