Mercruiser won't start

[andre757]

not that i can tell. it sounded ok. i am going to the boat shortly to do a compression check then remove the riser and manifold on the side where the water came out of the sparkplug hole. i hope i am not over my head here but it seems pretty straight forward. Thank you guys for all your help, this forum saved me a lot of money!

[Kevlar7r]

Replacing exhaust is pretty straight forward. It'll cost you about $700-$1000 in parts, but very easy to do. I would suggest change in pairs. If one side failed, the other is most likely right behind it.



There are many good resources on here and on the web that talk about what to look for when inspecting exhaust.



While you're there, check the oil again, especially after all the cranking to do a compression test. It may have soaked up more water from places in the engine and be muddy again. Don't want to leave that in there. Change it out. Filter too.

[andre757]

Hi guys, compression test:
starboard, 110,150,120,150 Port: 150,150,150,90 The 90 is on the first cylinder which had no water coming out. Water was coming out # 3 on port side. What do you guys think of those numbers? Thank you.

[Kevlar7r]

I would say those are pretty normal for an engine with some hours on it. A blown head gasket will give you basically no compression.



I think you may be in luck. Pull the exhaust. There should be nothing but pure black soot on the inside of the exhaust. I'll be willing to bet you see rust in there, combined with heavy corrosion in the water passages.

[andre757]

Ouf! Thank you for some good news. i started removing the riser on port side. i took the top screws off but ran into a challenge. the riser is connected to a big rubber hose connecting to a cast iron elbow. i loosen the hose clips but i still can't pull the riser up. Is there a trick to it? See attached pic https://www.dropbox.com/s/5kjzp015yc...riser.jpg?dl=0 Thank you. Andre

[Kevlar7r]

What I did was remove those bolts, then twist the riser relative to the rubber hose to break the seal. It you don't have enough vertical clearance to remove the bolts, lift them up enough that they are out of the header, then twist.



As a note, I coated the inside of the rubber couplers with grease to make reassembly easier.... And possibly aid future disassembly.





Edit, just looked at your pic. Ugh, I hate the studs. You're going to have to remove the manifold and risers together to be able to twist it and break the seal.



Or, take off the next joint down, if you can reach it.

[andre757]

ok. back in my truck, back to the boat, LOL Thank you. ttyl

[andre757]

Got it out. I hope you guys can see the pictures

[andre757]

... at the following link. Picture 17 is very interesting. Please let me know what you think when you have a chance. Thank you. Andre

https://www.dropbox.com/sh/zk3qeskqq...fHfnQw82a?dl=0

[Kevlar7r]

Suspicion confirmed. Your exhaust is toast. Looks like someone had cleaned up and painted over rust marks which may have indicated impending exhaust failure.



Replace both sides!

[Kevlar7r]

Squirt some wd-40 in all of your spark plugs holes, to displace any water that may remain.

[Kevlar7r]

Looks like your exhaust is the same as mine. Here is what I ordered, from go2marine.com. Best prices I could find. You will have to re-use the studs. May need to get a stud puller to remove them.

[mmwjr]

Agree time for new exhaust.

Compression reading should be with-in 10% for all the cylinders.

Based on the numbers I think the valves and leaking on the low cylinders. It's up to you if you want to have the heads done but you should be able to get a few more years out of the engine as is.

[andre757]

Thank you Kevlar7r ! Yes i will do both sides. Not sure about the painting thing i had the boat for only one year.

Just for my education purposes, it looks like the water got in the cylinder from the exhaust hole down to the cylinder. That explains it. Any thoughts on how it got down to the oil pan? Would the compression have pushed it in? Thank you for all you guys help. I don't think i would have had the will to do this work but this forum save me $$$$$.

[Kevlar7r]

You're welcome!


I'll bet the previous owner painted them so you wouldn't notice rust like mine looked like.




Water is much less viscous than oil and leaks past the pistons very easily.



Once you get up and running, change the oil and filter again after a few minutes of run time.

[Kevlar7r]

This is probably what it looked like before it was painted up.

[andre757]

What a great way to end the week. I went to Marine2go and order all the parts for both sides. I should be able to finish this towards the end of the week next week. I''ll let you know how it runs. Thank you Andre

[mmwjr]

Best of luck

[Kevlar7r]

Good luck. Use thread sealant on all of the little plugs you have to put in to the manifolds and such. I used regular plumbing thread sealant, white Teflon goop.



You double checked that those part numbers were right for your engine, right?

[andre757]

Thanks for the tip about using sealant. I hope they are the right parts. Over the phone i gave them my serial number and they told me i have a Mercruiser 350 mag which is accurate. We'll see on Thursday.

I have an electrical question while i wait for the parts. When i cranked the engine (no spark plugs) the cable to the battery (The big black one) becomes very hot. I disconnected the cables and did a test with a ohm meter. The big red one to the starter: meter shows OL which obviously means no contact with ground but when i check the orange cable from the alternator to the starter (while connected to alt and starter and get a reading. Is it normal? Just wondering if this is the cause for the overheat. Thank you. Andre