1989 Johnson 90-HP Engine: Smoke in Exhaust

[Kend]

My Johnson [1989 90-HP engine with variable ratio oil system or] VRO always smoked when I started it,

I was told [the cause of smoke in the exhaust on initial start-up of the 1989 Johnson 90=HP engine with the VRO system was because] the [spark] plugs had excess oil on them [due to some behavior only described as] by "injection."

In 2024, the [1989 Johnson 90-HP engine with VRO] was started. [During the time the engine was running at] idle [speed, there was smoke in the exhaust] and also there was [smoke in the exhaust] all the time while [the engine was] running at slow speed. [To the contrary when the engine] runs at high speeds, [the behavior is to] run perfectly and [to have] no smoke [in the exhaust].

The [difference before the engine was started in 2024 compared to when the engine was started in other years] was only that the the oil [reservoir] tank [was filled] to the top,

Q1: before I take in the [1989 Johnson 90-HO with VRO] engine for an inspection, what further checks should I perform?

The oil being used is the QuickSilver-brand premium two-stroke oil [and the gasoline fuel grade is] premium.

[jimh]

The presence of smoke in the exhaust of a two-stroke-power-cycle engine can occur in two distinct situations.

First, if the engine combustion chamber is being exhausted into cold and moisture-rich air, the formation of "smoke" can occur no matter what the content of combustion products related to oil in the fuel might be.

Second, the particular oil that is used and mixed into the combustion chamber with the fuel affects the amount of smoke in the exhaust. For best outcomes, use Evinrude XD100 oil, which produces very little (to no) smoke in the exhaust.

The level of the oil in the oil reservoir tank is very unlikely to affect the amount of smoke produced in the exhaust, compared to the atmospheric conditions or the the type of oil being used.

ASIDE: I use Evinrude XD100 oil in my two-stroke-power-cycle engine, and the only time there is a presence of "smoke" in the exhaust is then the atmospheric condition are cold air with high humidity.

[Kend]

I have been using the Quicksilver oil for several years and this is the first time the motor has had this smoking [behavior] at idle. The smoke seems to be white. [Unspecified advice obtained from the internet] suggests [the cause of white smoke in the exhaust] could be

• water in the fuel,
• an air leak in the fuel line, or
• an engine [malfunction].

I have ruled out the engine [malfunction] as the engine runs fine at a high engine speed.

I’m open to an oil change [here "an oil change" may mean a change to a different type of oil rather than just replacing the present oil with new oil of the same type] if that cuts out the initial start up smoke-- but I think maybe [the initial start-up smoke] could be [caused by something] other [than the oil in use].

Thank you

[Kend]

I looked up the XD100 oil. [Some unidentified resource] shows XD100 oil is for an E-TEC engine.

My 1989 two-stroke-power-cycle engine is not an E-TEC engine. The manual recommends SAE oil

I just want to make sure [XD100 oil] is compatible.

[jimh]

For an outboard engine manufacturer to recommend using an SAE graded oil as the lubrication for a two-stroke-power-cycle engine to be mixed with the gasoline fuel sounds like something from the 1950's.

Typically the lubricating oil that will be mixed with the gasoline for a two-stroke-power-cycle engine would be qualified to TCW rating, typically TCW-3 for a modern engine like a 1989 model.

The TCW-3 rating is

TC for two-cycle
W for water cooled
3 for third generation

More details about the rating of TCW-3 at

https://www.nmma.org/certification/oil/tc-w3

The reason that XD100 does not carry a TCW3 rating is because Evinrude never bothered to go to the expense of having it tested and certified. However, Evinrude permits the use of XD100 oil at about HALF the amount that a TCW3 oil would be used in their E-TEC engines. The XD100 oil is thought to be a synthetic base oil with excellent properties. Compared to SAE automotive grade oils it would be a much better lubricant.

Because you report that prior to just recently the oil you have been using did not produce the white smoke, perhaps there is no reasonable basis to begin to use a different oil to see if the new occurrence of white smoke is related to the oil.

Note: the QUICKSILVER brand is generally just a re-branding of products that originated under the Mercury Marine brand. As far as I can tell the purpose of having two brands selling the same products is to permit vendors who are not authorized Mercury engine sales dealers to be able to sell products for use in Mercury engines. For example, you can probably find Quicksilver oil sold at a store like Walmart, but you won't find Mercury-branded products sold there.

[jimh]

If a two-stroke-power-cycle engine exhibits a lot of smoke on start up but later runs without smoke, the most reasonable inference for the cause of excessive smoke on engine start is that the combustion chambers contained excessive unburnt oil. A typical cause of unburnt oil remaining in the combustion chamber after the engine was shut down and not started for several hours or days is that fuel containing a mix of gasoline and oil was left in the combustion chamber at shut down, and over a period of several hours or longer the gasoline evaporated while the oil remained behind.

This behavior will occur when an engine has been sitting unused for a long period, and perhaps was intentionally over-oiled for storage. The excess oil will burn off for a few minutes at idle speed operation, with the duration before no smoke depending on how much oil was in the combustion chambers.

The same situation can occur in the reservoir bowl of a carburetor where the fuel in the carburetor contained a mix of gasoline and oil. Over time the gasoline evaporates, leaving only oil behind. At the next engine start the new fuel introduced into the carburetors mixes with the residual oil, resulting in the ratio of oil to gasoline to increase. The increase in the ratio of oil to gasoline results in more smoke in the exhaust, persisting until all the excess residual oil is washed out of the carburetor bowls.

[Kend]

The outcome: the cause of the problem with the 1989 Johnson 90-HP engine having smoke in the exhaust was found to be the fuel line had an air leak.

The remedy included:

• replacing eight-feet of fuel hose;
• changing the fuel can spout;
• changing the fuel intake connector at the engine; and,
• just to make sure, having the carburetors cleaned by a service technician.

The 1989 Johnson 90-HP now runs like new with no smoke in the exhaust.

[jimh]

Thanks for the follow-up post with the remedy to the problem of smoke in the exhaust.

However, I would like to hear an explanation of how an air leak in the fuel hose causes smoke in the exhaust of a classic two-stroke-power-cycle outboard engine with carburetors.

Also:

Q2: how did replacing the spout on the fuel can have an effect on reducing the smoke in the exhaust?

[Kend]

I had the [1989 Johnson 90-HP engine] serviced by [Lockeman's Hardware and Boat] in Detroit. They believed the old [fuel hose] connection fittings were leaking fuel, and the [fuel hose] connection at the engine was a cause of the smoke.

I was told my problem was most likely an air leak problem, so I replaced the 8-foot fuel hose before I took it in [to Lockeman's] but the engine still smoked.

That’s all I know. [Now the engine exhaust has] smoke at start up, but at idle I can barely see any smoke [in the exhaust].

[jimh]

Kend--thanks for the follow-up. I am very familiar with Lockeman's Hardware and Boat in Detroit, and they are expert in the service and repair of OMC engines, as they sold them for over 100-years at that same location. And, even better, they are just great people to work with, really the best possible dealer that you could take an OMC outboard engine to for service.

I do have some confusion with several of the terms and descriptors you have used in your narrative.

For example, I cannot believe that the owner's manual for a Johnson engine made in 1989 contains a recommendation to use a lubricating oil for mixing with the gasoline that has an "SAE" rating. The recommended oil to be used with a two-stroke-power-cycle engine for mixing with gasoline fuel is just about universally recommended to be compliant with the marine rating called TCW-3. Perhaps you are confusing or conflating "SAE" with "TCW-3".

Also, I cannot understand your reference to "the fuel can spout." Whatever might be wrong with the spout on a fuel can, it would not be possible for that to change the operation of the engine. When the engine is running the fuel is coming from the fuel tank not from the fuel can. The fuel can is not connected to the engine. Again, perhaps your use of "fuel can spout" should have been stated as "fuel tank pickup tube." Note that in the Evinrude fuel system the fuel tank is vented to the atmosphere. A pick-up tube in the fuel tank extends to very near the bottom of the fuel tank, and that is where fuel is pulled (by suction) into the fuel hose. If the fuel pick-up tube is not air-tight and its end submerged in the gasoline fuel, then air can enter the system at that point.

Perhaps you can follow-up on those two very odd terms with some clarification.

Also, you described the 1989 Johnson engine has having a "VRO" system. This may be the key to understanding why ingress of air into the fuel hose feeding gasoline to the engine could have caused a problem that exhibited the symptom of excessive smoke in the engine. The basis for that may be as follows: in the VRO oil mixing system, the fuel and the oil are mixed together in a mixing pump. The pump is very thoroughly described in an article reproduced in the REFERENCE section at

VRO STORY--The Myth of the Mixer
https://continuouswave.com/whaler/reference/VRO.html

The article on the VRO contains this warning:

Air leaks and/or fuel restrictions will affect the VRO and usually show up as excessive oil consumption, smoking, and fouling plugs.

[jimh]

I was told my problem was most likely an air leak problem, so I replaced the 8-foot fuel hose before I took it in [to Lockeman's] but the engine still smoked.

My inference from that account is that the fuel hose was not the source of the air ingress. Apparently the connection between the fuel hose and the engine might have been the source of the air ingress into the fuel system, or perhaps more likely the fuel pick-up tube in the fuel tank was introducing air.