SUGGESTIONS NEEDED diagnosing blue smoke problem

[dbm_nj]

I have a 1994 Mercury 115hp 4 cylinder that is spewing large amounts of lite blue smoke.
1. I purchased a compression tester and found good results:
132psi top cylinder
132psi 2nd cylinder
140psi 3rd cylinder
140psi bottom cylinder

2. I purchased a SELOK repair manual but it doesn't provide any
troubleshooting adviCe for this problem.

3. I don't know what to do next. PLEASE PROVIDE SUGGESTIONS

 

[BR]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

While it is not unusual for a 2 stroke to smoke some, you shouldn't be leaving a blue cloud behind you everywhere you go. Sounds like a fuel/oil mixture problem with too much oil. Do you premix or does this motor have oil injection? If premix, are you using correct ratio and is the fuel fresh?

 

[hkeiner]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

If the motor has oil injection, check that the oil pump is correctly adjusted. The shop manual for you motor will have instructions.

The below guide is from an old Merc manual that I have for a 115hp, but I don't know if it applies to your particular motor as you did not provide your motor's serial number.

 

[dbm_nj]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

Update: This engine has an oil injection system.

The SELOK manual describes the oil injection system - but I am a bit confused about the Air Compressor and Check valve in the oil return hose - how do these contribute to the operation of the system? Could a faulty Check Valve be the cause of my problem?

Also, there are no oil pump adjustments discussed in the manual.

 

[saumon]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

No, the check valve prevent the oil from entering the fuel line.

I'd try a decarb with Seafoam, can't hurt.

 

[j_martin]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

Update: This engine has an oil injection system.

The SELOK manual describes the oil injection system - but I am a bit confused about the Air Compressor and Check valve in the oil return hose - how do these contribute to the operation of the system? Could a faulty Check Valve be the cause of my problem?

Also, there are no oil pump adjustments discussed in the manual.

Get the right manual.....That is a genuine Mercury shop manual.

That one is relatively simple, and the problem is probably in the linkage adjustment between the throttle and the VRO pump. Happens a lot.

Another thing that happens is the crankcase check valve, which should let the pressure off when you shut down doesn't, and a bunch of oil pushes forward into the fuel lines. Then it smokes, or even won't start.

hope it helps
John

 

[hkeiner]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

If you provide the serial number of your motor and/or indicate if there is a remote oil tank on your oil injection system, it will help with providing you the correct advice.

If your oil injection system does not have a remote oil tank and you refill the oil into a tank under the cowl, then the oil is gravity fed from the oil tank under the cowl to the metering oil pump, and there is no crank case check valve on the motor. If however, your motor has a remote oil tank inside the boat and it feeds the reservoir tank under the cowl, then there is a crankcase check valve on the injection system. This check valve provides air pressure to the remote oil tank pushing oil into the reservoir tank under the cow to keep it full. If this check valve provides too much pressure or if it does not relieve the pressure in the remote oil tank after the motor is shut down, it will cause too much oil to be pushed past the metering oil pump and into the fuel line causing excessive smoke. I had this problem on my 150Hp motor and replacing this check valve solved it.

I have an old Merc shop manual for a 115hp, and it shows that there is NO remote oil tank on this motor (see below pic). However, your motor may be different if it has a different serial number that the range covered by my manual (SN 0D283222 and above).

 

[dbm_nj]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

Get the right manual.....That is a genuine Mercury shop manual.
hope it helps
John

Where can I find a Mercury Shop Manual? If I can buy it on-line please send me a link.

Thanks!

 

[dbm_nj]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

If you provide the serial number of your motor and/or indicate if there is a remote oil tank on your oil injection system, it will help with providing you the correct advice.

The tag on the transome is blurred so I can't see the Serial Number - is there some other place where it is stamped into a metal part?

The engine has an oil tank attached to it - not a remote tank.

Your help would be appreciated.....

 

[hkeiner]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

The engine has an oil tank attached to it - not a remote tank.

Since there is no remote tank, there is no crank case check valve. The diagram shown above should then match your oil injection system. The most likely cause of excess smoke on your system is an incorrectly adjusted oil pump. The diagram I provided earlier indicates how the marks should line up. Check your motor and see if the marks line up correctly and report back. Just a suggestion...

 

[dbm_nj]

Re: SUGGESTIONS NEEDED diagnosing blue smoke problem

Thanks for all of your help! The engine is running fine now due one of two changes that I made. I don't know which solved the problem.

1. I replaced the 2psi check valve that sits beween the oil pump and the fuel pump.

2. I adjusted the oil pump linkage according to the description in my original "outboard engine installation manual" which is the opposite of what the Mercury Service manual describes. There are 2 lines on the oil injection arm and I chose the mark listed in my original manual.