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Mercruiser 3.7

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dj32nc

New member
Hello everyone. Im very new to boating and also this forum, so if I do something wrong, I apologize but will correct it. So heres my story...
1988 Wellcraft 190 classic. 3.7 mercruiser I/O. Bought it, ran fine for 2 trips out. Overheated, had a new impeller put on. Fixed. Took out 3 more times, ran fine. Last time we went out we rode around most of day, and got in the lake a few times. The last time we stopped and turned boat off to get in water. Couldn't get it to crank back up. towed in. Took it home. Friend who is a decent mechanic said needed a new carb. Got the new one, put it on. Started up but ran very rough. Motor was shaking about every minute or two. Also put on a new fuel pump, fuel filter, 2 sets of plugs. Friend found during running a leak at exhaust manifold. Got new gasket and had put on. Still running rough. Just ordered new dist cap, rotor, points, and condenser. Where I'm puzzled is, what could it have been to make it not start (would turn over fine until battery died) all of a sudden after running fine all day? Im not very mechanically inclined about timing, and points. Just seems since it happened all of a sudden that it would be one quick repair. Just finding what part is a job. Please Help!
Thanks.
 
Reddman said:
Pull your spark plugs & check for water. These motors don't like getting hot & are known for blowing head gaskets.
Click to expand...

I Checked but did not see any water or moisture... any other suggestions? Thanks for the response. It ran fine for about 3-4 trips after it overheated that one time..
 
You may have a water leak into the cylinders from the exhaust manifold (due to overheating). Or a head gasket could be the trouble. I'd start by doing a compression test.

Jeff

PS: You can borrow a tester from Auto Zone.
 
dj32nc said:
I Checked but did not see any water or moisture... any other suggestions? Thanks for the response.
Click to expand...

That's the weird part. After it overheated and I replaced the impeller, we took it out only like three or four different times and it ran fine. I have also replaced the exhaust manifold gasket. One of my friends took it to one of his Marine shop buddies and that a compression test and said everything was fine. I guess that's why am so confused as to why it's not running good.
 
That IS confusing. Only thing to do now is go back to basics: Check timing, spark advance, fuel pressure in run, etc.

Jeff
 
Here's my suggestion:

Use the tried and proven P of E (process of elimination) when doing any mechanical testing, repairs and/or replacements.

This means to fully test, check, and perhaps re-test and re-check prior to parts replacement.

This also means to test/check/replace one item and one item ONLY at a time before moving to the next suspect item.

When used systematically and methodically, the P of E will NOT let you down! It never will!

It will also leave you better equipped to diagnose similar issues in the future.


***************************************************

As for the Mercury Marine Corp. (their own design) 3.7L in-line 4 cylinder Engine, there were severe problems with this engine, of which explain it's relatively short life span in Mercruiser's line up.

Charging system Stator issues.
Liquid cooled charging regulator issues.
Engine circulating pump "impeller" is camshaft end driven.
The oil laden crankshaft area is separated from the ethylene glycol area by a special seal.
The front cover that encases and separates this area will occosionally warp.
This Engine incorporates an aluminum cylinder block with a cast iron cylinder head.


Point being...... if the cost to repair this engine and to get it operating correctly becomes excessive, cut your losses now and go with a different engine.




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dj32nc said:
I Checked but did not see any water or moisture... any other suggestions? Thanks for the response.
Click to expand...

So today, I changed our the dist cap, rotor button, condenser. Engine is running like a top except for some carb sputter, and after about 10 minutes of running it overheated... any ideas?
 
dj32nc said:
So today, I changed our the dist cap, rotor button, condenser. Engine is running like a top except for some carb sputter, and after about 10 minutes of running it overheated... any ideas?
Click to expand...

Yes......... Use the tried and proven P of E (process of elimination) when doing any mechanical testing, repairs and/or replacements.

I would begin at the seawater pump.
Work your way forward and inspect each and every component...... especially the ones that you would not normally suspect.
This means the vertical tube coming out of the seawater pump, any hoses, fittings, T-stat housing rust scale blockage, back flow prevention flappers, look at the mixing chamber seawater port at the exhaust elbow, etc.
Leave no stone unturned!



.
 
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