Volvo 850, S70, V70 Lawnmower Syndrome Theory - Video

[rspi]

This video explains the lawnmower theory in case anyone want to watch and link later.

The symptoms are, all of the sudden your car does not start. Usually after a brief start and shut down, as in moving the car 20 feet or so. Far enough to get the "lawnmower" out of the garage. The car sits a little while and when you return, it cranks but will not start. So you go through the process of trouble shooting the no start condition and learn that you have little or no compression across the board.

The solution is to pull the plugs, air them out or replace them, pour a little oil in the cylinders to wet them with oil (instead of fuel), put everything back together and crank away. Within a minute the car will build the compression needed to fire and your problem is gone, likely never to return.

[precopster]

I don't know about its "rareness" Robert.
It happened 3 times on my 960 in 2 years and that engine had lots of blow-by, ridges at the top of cylinder bores and around 15% less power than it should have had. PCV was already handled.

Once owners of cars log in here at MVS or other forums they gain the knowledge of how to deal with it next time and we move on.

[polskamafia mjl]

I've always taken great care to avoid experiencing lawn mower syndrome but I've only ever heard of Volvos being affected by it. Do other cars suffer from this problem too or is it just a Volvo thing?

[rspi]

I think other cars just get flooded but don't loose compression.

[precopster]

I've started our other Volvos on very short runs (15 secs or less) and never had a problem. I can repeat this dozens of times and have no issues. However they don't have worn cylinder bores.

The later cars have oil squirters built in to the block area which squirt the bore.

I think the improvements begin in 2000 with the newer castings and shimmed tappets.

[jimmy57]

Other cars suffer too. 4 valves per cylinder and hydraulic tappets are the ingredients and then you add city driving with lower revs and to complete it you run car from cold start for a few seconds and then shut it down. If you do the brief run twice it has a much greater chance of occurrence.

Not all failed to run Volvos are LMS. I first saw "Lawn Mower Syndrome" in an Infiniti tech bulletin.

LMS is deposits on exhaust valve stems that get partly dissolved by the water and fuel fog that comes out of exhaust ports on cold started engine. Then you add to that the near fuel fouling of spark plugs from the brief prior run.
Now you have a thick sludge on stem that slows the light valve spring closed valve. You crank engine over and the quick to build oil pressure oil pump gives hydraulic tappets oil pressure and when cam lobes are near base lobe( the oil feed hole to tappet is aligned when valves are closed) the tappets pressurize and extend because the valve is not keeping normal force on the tappet due to being dampened by the sludge. The tappets will keep the valves off seat less than a 1 mm and now there is little to no compression and the engine dies and when another attempt is made to start the engine spins over way too fast for normal and will not run.
Volvo's quick fix was a different spark plug that has greater fuel fouling resistance. The other change in production was to have the tappet maker slightly increase clearance between tappet piston and its bore.
Excessive fuel fouling will give you no start in similar situation but without the extra fast engine cranking speed of no compression. Engines with wear will lose compression when cold because worn rings and cylinders make for very poor sealing. This leads to fuel fouling during cranking due to inadequate compression to support combustion.
Stuck open tappets causes low compression and the same end result.

The true test of LMS is to do cylinder leakdown and see the air escapes into exhaust.
When the engine has LMS the cure is to crank engine over long enough tht the exhaust valves get worked and freed and the tappets then relax when the valves now keep pressure on them as lobes lower valves back to seats. Fresh plugs will makes engine start more readily but if there is low compression then it will still take long cranking. This goes against normal practice but you must keep your foot on the floor while cranking and crank over for a minute to 90 seconds before giving starter a rest. If the engine has LMS then it has little compression and the starter load is very low and it will not overheat easily in that case. cranking a normal compression engine over that long would be bad for starter.

The 2000 and later engines with solid tappets have no mechanism to push open valve and hold it off seat. These can be flooded though.

One of the reasons Volvo started using the feature where you turn key to start position and the system operates starter until engine runs or 5 seconds is reached (Autostart) is to address operators doing short start bursts. The ECM does high fueling the first two engine revs while crsanking to get cold engine to start. If you do short starter bursts then you are repeating the overfueling and will flood engine. Autostart cures that operator caused problem.

[osmium]

I've always taken great care to avoid experiencing lawn mower syndrome but I've only ever heard of Volvos being affected by it. Do other cars suffer from this problem too or is it just a Volvo thing?

It has happened on my 99 Civic.

[rspi]

Hey Jim, thanks for the thorough information.

[taxi]

Hi!
It's funny, I almost did this on my fathers civic too, a -97. Cold start to get the car in to the garage, real hard start after that.

And Jimmy57: I was so sure about lawn mower syndrome being nothing more than oil film dissolved by excess fuel. To which a logical solution is adding oil and unplugging injectors, and turning the engine over with the starter for a few seconds until it slows down (because compression returns), Then plug in injectors and start the car.

This is what I have tried and succeeded with, it just feels wrong to blame something else..? Please correct me if you have the energy

[airbusguy]

Wow, both my 95 850 and 98 S70 were affected by this, both NA. I always just ran the engine until the temp gauge showed some heat. Eliminated the grief from the wife thereafter.