1990 Mercury 150 smoke coming from cowl

fishngo

Recruit
Joined
May 18, 2010
Messages
2
Hello, need some help with troubleshooting an issue with my 1990 mercury 150, it runs and starts fine. At Idle I have exhaust smoke coming out of the engine cowl, soon as you throttle up it stops and runs out the prop as normal. I was told it needs a powerhead gasket but I dont see engine smoke signs coming from around powerhead area, not sure what to be looking for and what the typical issue is, I have done alot of work to these but this is a new deal for me to figure out,
thanks for any advice
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Re: 1990 Mercury 150 smoke coming from cowl

Remove the cowling and observe the base of the motor, way down low in the cowling. That is where the smoke should originate from. If so, try some silicone to pulg it up. If that fails, you will need to pull the powerhead and replace the gasket.
 

ufm82

Master Chief Petty Officer
Joined
Jul 29, 2003
Messages
827
Re: 1990 Mercury 150 smoke coming from cowl

Before you start pulling the engine apart look at this first. I have a '93 150 and had a similar issue- smoke would come from the front of the engine at idle and I thought base gasket or some other gasket was leaking, allowing exhaust into the engine compartment. However, I found the culprit and it was a cheap and easy fix.
Remove the cowling. The lower cowling is in two pieces- right half and left half. If you look at the rear of the lowers right in the center you will see a small square port that is the above water exhaust tube. It looks like a square rubber grommet from the outside. Look in the engine compartment and it looks like a z shaped rubber boot. Mine was torn where it went through the cowlings and it allowed exhaust gas into the engine area. That left an oily film in the lower cowlings and made a mess. It also caused the smoke from the front of the engine while idling. I found the piece on eBay of all places, replaced it an POOF- no more smoke or mess. I think it cost me $15.

Here's a picture of the piece I bought- It's #38

http://www.usboatsupply.com/Mercury_Mercruiser_Parts_Catalog3a.php?mc=01&ms=7240&si=573

Find your engine and then click on "driveshaft housing and exhaust tube". It says mine has been discontinued but I found one anyway. Got lucky I guess.

UFM82
 
Last edited:

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: 1990 Mercury 150 smoke coming from cowl

Before you start pulling the engine apart look at this first. I have a '93 150 and had a similar issue- smoke would come from the front of the engine at idle and I thought base gasket or some other gasket was leaking, allowing exhaust into the engine compartment. However, I found the culprit and it was a cheap and easy fix.
Remove the cowling. The lower cowling is in two pieces- right half and left half. If you look at the rear of the lowers right in the center you will see a small square port that is the above water exhaust tube. It looks like a square rubber grommet from the outside. Look in the engine compartment and it looks like a z shaped rubber boot. Mine was torn where it went through the cowlings and it allowed exhaust gas into the engine area. That left an oily film in the lower cowlings and made a mess. It also caused the smoke from the front of the engine while idling. I found the piece on eBay of all places, replaced it an POOF- no more smoke or mess. I think it cost me $15.

Here's a picture of the piece I bought- It's #38

http://www.usboatsupply.com/Mercury_Mercruiser_Parts_Catalog3a.php?mc=01&ms=7240&si=573

Find your engine and then click on "driveshaft housing and exhaust tube". It says mine has been discontinued but I found one anyway. Got lucky I guess.

UFM82

Agree, that's usually the culprit.
 

fishngo

Recruit
Joined
May 18, 2010
Messages
2
Re: 1990 Mercury 150 smoke coming from cowl

I do have an oily film all over the bottom in the cowl area, I have two 150's the one having the issue has two small ports, its an 89-90 model, the 91 model has the boot your talking about, perhaps it has a boot but is visible on the inside, I will look, also I will slide a bin up to the motor and act as if its in water with pressure on the prop exhaust to see if it leaks around the base as well,
two great things to check, thanks for the advice !!! !!!
 
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