120 hp Mercruiser issues

[GrimReefer]

i recently bought a 1979~ 18' glasply powered by a 120 hp mercruiser i/o and had it fully serviced,all fluids and impeller changed (for 550 bucks...). I took her out for a burn on the lake last night, it fired right up but was spitting out white smoke (possibly just steam?) and was running a little warm maybe an eighth of an inch below the red. a friend of mine suggested i may have a leaky head gasket and water is dripping onto the engine around the heat exchanger. I'm wondering if any of you may be able to diagnose this problem for me, thanks guys

 

[CheapboatKev]

Re: 120 hp Mercruiser issues

Welcome Aboard!

Check the oil...is it white and milky? was it steam or white smoke? If white smoke, maybe just a poor running carb, bad plugs, rings..any number of things.

I have that same Temp gauge...I am going to replace mine with actual temps on it, rather than green-yellow-red...


Good luck..many far smarter than I will stop in.

 

[GrimReefer]

Re: 120 hp Mercruiser issues

Thanks for the speedy reply, i will check the oil when i get home from work but I am sure that the mechanics just did a complete oil change on July 29th. This is my first boat and i'm still just learning the basics in marine repairs and how they should run. Thanks for any advice and all the help I can get.

 

[IES99]

Re: 120 hp Mercruiser issues

There is lots of good information on this iboats forums and also at the following link:

http://mercstuff.com/howdoi.htm

 

[GrimReefer]

Re: 120 hp Mercruiser issues

Ran her for a good 4- 5 hours the other day, oils not white or milky, wasnt nearly as much smoke comin out either. checked the oil today though and it was under the add line.. and there was also oil covering the entire top of my engine, it seems to be coming from about a 3/4 to 1inch tube on top of the engine (comin out of the valve bank? someone mentioned, sorry i dont know what it exactly is) and another mentioned its from blow by and that all the piston rings and so on were hooped, is there any sort of half *** fix to run this boat for the season without having to keep gallons and gallons of extra oil onboard? shts pricey these days.. im half certain that i may need a rebuild so if theres another way please let me know, because i certainly dont have the time or money right now
thanks
cole

 

[6meter]

Re: 120 hp Mercruiser issues

The tube is the crankcase breather and should be attatched to your flame arrestor/air cleaner. If there is excessive smoke coming out, the rings would be a reasonable cause. Sorry but there is no snake oil to fix it.

 

[GrimReefer]

Re: 120 hp Mercruiser issues

There is no exessive smoke coming out anymore, its just the fact that oil is coming out of the breather tube. Would this be caused by blow by?

 

[searay3]

Re: 120 hp Mercruiser issues

Blowby is caused when the crankcase is being pressurized. Could be a couple of things. Start with a compression test and see what you are working with. If it's low a leakdown will give you an idea of where it is broken. Anytime oil is coming out of those tubes with any kinda of quantity, you will be tearing it down anyway, but the tests will give you an idea of where to look once you have it apart.

 

[GrimReefer]

Re: 120 hp Mercruiser issues

Compression test done, 150, 130, 140.... then 0 on the furthest back cylinder, bolts on the valve cover were hand tight for some reason, not sure what to do now, wait for the fishin season to die down and tear it apart this winter

 

[chaparall villain 2]

Re: 120 hp Mercruiser issues

0 psi sounds really wierd to me if it is developing no compression it seems like not only rings but maybe something in the head or valve train, sounds to me like one of the valves is sticking open and not letting compression develop but i agree its probably going to have to come apart and i dont know how much i would use it at all until then ... a cylinder thats dead could cause fuel contamination in oil and maybe do more damage to the cylinder wall