1990 Mercruiser 7.4L Heat Risers??

[Darin Jordan]

Hey Gang...

OK, the short story is that my 1990 Maxum 24SCR (24' Suncruiser), which has a 7.4L Mercruiser w/ Bravo 1, appears to have some issues with the heat exchangers on the exhaust. The boat only has 286 hours on it... and has been very well cared for for the most part.

I noticed a couple of years ago that it would loose about 1/2 gallon of Anti-freeze from the sealed side of the system after sitting for a couple of months... and when I'd run it, a bit of white "steam" would come out of the water where the exhaust/water exists through the transom... I suspected that the Heat Riser gaskets were likely the cause, but the plugs and all looked perfect, so I haven't worried about it...

Well... now I need to! I haven't run it since last summer, though I've started it on the trailer over the winter... It's generally been sitting. I keep a heater in the engine bay over the winter, so it's been warm as well...

I couldn't get it to turn over... wouldn't even crank a revolution, and after removing the battery from the suspect list, I knew I had issues...

I pulled the plugs last night and found that the 3, 5, 6, and 8 cylinders had anti-freeze in them... #8 was the reason it wouldn't turn over (trying to hydraulic)...

Obviously, it's time to fix the problem.

My plan is to first, fog the hell out of the motor to keep it from corroding more then it may have already done... I turned it over with the plugs out last night and with the plugs out, it cranks over just fine... All of the anti-freeze pumped out of the cylinders... So I'm going to oil everything down and make sure no further damage occurs in that regard...

Next, I'm going to change the oil in the crankcase to make sure no antifreeze got in there... Dipstick doesn't show any, but I know that antifreeze will take out a bearing in a heartbeat, so it's better safe. It's about time to change it anyhow...

After I do those two things... I'm going to put new plugs in and see how it runs... If it runs fine, without any vibrations or weird noises or overheating, etc... then I'll be fairly comfortable that the motor itself is fine...

Once I've confirmed that, I'll remove and do what needs to be done with the exhaust/heat risers, and whatever else I might find...

I know there are some boating experts out there... does this sound like a reasonable plan of attack??

One other thing that I've considered is seeing if I could replace the stock Q-Jet with some kind of Throttle-body injection system or ??? Would love to get rid of the ancient "choke-stove" style carb and get a modern electronic FI on there... if for no other reason than just for the starting performance and smooth operation...

Anyhow, if anyone out there has experience with any of this, I'd be open to advice... I can fix it, but it never hurts to see what others may think or have experienced...

Thanks!

[Eodman]

Darin - semtex packed around the riser, remote detonator, drive it out in the middle of the lake/ocean/bay dive into water swim back to shore hit button! Problem solved!

[Doby]

Are you running a BEC................ (sorry, couldn't resist)

[Darin Jordan]

Are you running a BEC................ (sorry, couldn't resist)

I wish... damn batteries in a boat are a pain in the A$$

And... the C4 thing did come to mind... but there is a less obvious option... it's insured... by the way...

I saw a boat onetime that lost one of it's fresh-water cooling lines... filled the entire engine bay with water before they figured it out and damn near sank the boat.... Hmmmmmmm

But... I couldn't do it... this was my Dad's boat and I should take care of it...