Mercruiser 170 Closed Cooling Issues

[mutiny]

BONDO... I need ya on this one

I have a Mercruiser 170 with a closed cooling system. It has been leaking down coolant and you can smell it clearly in the exhaust. Engine compression test 160 across the board. I hooked up a cooling system pressure tester and pumped up the cooling system to 10lbs to see what was happening. I listened in all of the obvious places and searched for leaks externally. After removing the spark plugs I listened to each cylinder individually but could not hear a thing. I decided to run my bore scope into the spark plug holes only to find that the #3 cylinder is filling up with antifreeze. There appeared to be a little bit in #4 but not confirmed that it was antifreeze. I guess my question would be, in the forums experiences, what end should I start at? intake manifold gasket, exhaust manifold gasket, head gasket, anything else or all of the above?

I realize that I'm trying to take a short cut by asking the community and not just tearing into it to find a problem myself BUT I'm asking if anyone knows of a known problem with this engine, or has had the same issues? I know that this engine has a known issue between #1 & #2 being to thin and cracking but this does not appear to be the case here.

This engine runs great and starts right up. It runs best when the antifreeze reservoir is empty because then the #3 cylinder runs without the intrusion of the antifreeze . Once I add antifreeze while running, you can definitely hear the engine start to draw in the antifreeze and begin to run a little rougher. Hopefully my description helps shed some light on the subject. Thanks in advance.

 

[Eric 3.7LX Alpha 1]

]BONDO... I need ya on this one [/SIZE]

I have a Mercruiser 170 with a closed cooling system. It has been leaking down coolant and you can smell it clearly in the exhaust. Engine compression test 160 across the board. I hooked up a cooling system pressure tester and pumped up the cooling system to 10lbs to see what was happening. I listened in all of the obvious places and searched for leaks externally. After removing the spark plugs I listened to each cylinder individually but could not hear a thing. I decided to run my bore scope into the spark plug holes only to find that the #3 cylinder is filling up with antifreeze. There appeared to be a little bit in #4 but not confirmed that it was antifreeze. I guess my question would be, in the forums experiences, what end should I start at? intake manifold gasket, exhaust manifold gasket, head gasket, anything else or all of the above?

I realize that I'm trying to take a short cut by asking the community and not just tearing into it to find a problem myself BUT I'm asking if anyone knows of a known problem with this engine, or has had the same issues? I know that this engine has a known issue between #1 & #2 being to thin and cracking but this does not appear to be the case here.

This engine runs great and starts right up. It runs best when the antifreeze reservoir is empty because then the #3 cylinder runs without the intrusion of the antifreeze . Once I add antifreeze while running, you can definitely hear the engine start to draw in the antifreeze and begin to run a little rougher. Hopefully my description helps shed some light on the subject. Thanks in advance.

Come on dude.. he doesn't even have a 470

J. K. Bill knows his stuff..


Manual 8 has 12 causes for water on top of the pistons.

click on this link to open up Service Manual# 8 to the correct page:

http://boatinfo.no/lib/mercruiser/ma...iser8.html#/50

have you overheated at all recently?

 

[Bondo]

BONDO... I need ya on this one

Ayuh,..... I guess you missed the memo,.... I've never put a wrench to a 470,....

Only causally glanced at 470s layin' in junk piles 'round various marinas,....

If I had a 470, 'n it had a problem, I'd be huntin' advice from Eric, 'n Terry though,.....

 

[mutiny]

Come on dude.. he doesn't even have a 470

J. K. Bill knows his stuff..


Manual 8 has 12 causes for water on top of the pistons.

click on this link to open up Service Manual# 8 to the correct page:

http://boatinfo.no/lib/mercruiser/ma...iser8.html#/50

have you overheated at all recently?

Haha.. Well Bondo has usually chimed in on a lot of my posts so I thought it was worth a try. Thanks for the link to the manual I have the hard copy here at the shop as well. I was just hoping that with my description it may have rang a bell with one of you fellas. This site is an awesome resource with decades of experience and I appreciate your input Eric. Bill's as well .. Even if he doesn't have one of these fine, fine 470's I'll not disregard any of his suggestions lol.

Eric, this boat has a history of overheats. The previous mechanic pressured the customer into doing an entire engine rebuild last year which took him out of the entire boating season. He has gone through 3 head gaskets after the rebuild until last month, and now I get a crack at it. It was handed back to him backfiring and belching up engine creme. I took Bondo's advise and dug into the carbs instead of the heads for the backfire issue and the carb rebuild and a tune-up kit cleaned up any of the backfiring and is now running smooth (thanks Bill). The reason I assumed heads is because the customer told me that the heads were never rebuilt with the rebuild of the engine. Even today the heads remain whatever they were before the engine rebuild. Since the boat was handed back to him, the coolant needed to get topped off after a few hours of running. I guarantee that this engine got hot on each trip since the antifreeze was never high enough to circulate through the engine properly. Customer justified it as "I never go full throttle, and don't go far". After a lengthy discussion about how the distance or speed he travels at doesn't matter, he promised to listen to my advise from now on.

So, to make a LONG story LONGER.. Yes it has overheated I'm assuming but never set off alarms.

 

[Eric 3.7LX Alpha 1]

Man to keep pulling the head off and not have it checked out at a machine shop is crazy.

Loss of coolant has several possible causes,
http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/244


The three I'd try testing could be:

Cracked or warped head

Improperly installed gasket between exhaust manifold and the exhaust elbow. (Happens quite a bit)

Cracked exhaust manifold

The cooling system is closed, and designed to hold pressure. So I think I would try and pressure test each component that is suspect separately.

The engine block has cooling water enter it from the hose on the intake manifold and exit the head in the front. You could disconnect these two hoses and rig up a pressure tester by capping one end off and install a pressure gauge and test rig using plumbing fittings and hose clamps. Pressure test less than the rating of the radiator cap maybe 10-psi.

Do the same with the exhaust manifold.

 

[mutiny]

Man to keep pulling the head off and not have it checked out at a machine shop is crazy.

Loss of coolant has several possible causes,
http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/244


The three I'd try testing could be:

Cracked or warped head

Improperly installed gasket between exhaust manifold and the exhaust elbow. (Happens quite a bit)

Cracked exhaust manifold

The cooling system is closed, and designed to hold pressure. So I think I would try and pressure test each component that is suspect separately.

The engine block has cooling water enter it from the hose on the intake manifold and exit the head in the front. You could disconnect these two hoses and rig up a pressure tester by capping one end off and install a pressure gauge and test rig using plumbing fittings and hose clamps. Pressure test less than the rating of the radiator cap maybe 10-psi.

Do the same with the exhaust manifold.

Great idea! i will head out and get some hoses and clamps to see if I single out the exact zone it is leaking in. Hopefully the head isn't the problem. I'd feel bad for the guy after all the money he has sunk into this engine already.

 

[stonyloam]

Hey welcome to the club. OK yank that head off and take whatever cheap crapo head gasket they used off and toss it in the trash, then order a genuine OEM Mercruiser head gasket (designed specifically for that engine) , yeah $80 but worth it. Take the head to a shop and have it checked, and a valve job. Ask the machinist about hardened exhaust seats. Then do the stuff Eric mentioned and you should be OK. Once you get it running right you will like it. Yeah don't ask Bondo about 470's he is shall we say.............. Unimpressed with the design LOL!

 

[mutiny]

Thanks for the post Terry! I'm quickly becoming "unimpressed with the design" myself. This thing has become the most complicated 4 cylinder motor I've worked with in a long time.

 

[nola mike]

I wouldn't jump on everything Terry is saying quite yet. Are you pressure testing with the system drained? Do you have an aluminum exhaust manifold? Less likely a problem than the earlier cast. Pooling on #3 is most likely a bad riser/manifold gasket or leaky riser, though certainly the other problems the guys mentioned must be considered. However the gasket is easy to replace and cheap (heh, I've unfortunately done it more times than I'd like), so starting with that and then pressure testing wouldn't be a bad idea. Worst case you've lost an hour and $10. My cheapo hg is on at least season 4, though if i did it again I'd go with oem.