View Full Version : maximum time engine off

9th June 2007, 10:01 PM
Hello there,

I was wondering what is the elapsed time you consider as a maximum for your engine to be off when running on WVO.
I find that when I am in WVO mode, if I let the engine off for more than 30 minutes, the start is "too smooth", as if the explosions in the cilynders were too weak. Besides, I am having some issues with carbon build up in the injector tips. At the moment I am not sure if this has to do with WVO contamination in the diesel tank or if the carbon build up occurs right after starting the engine after 30 minutes rest as the oil may be too thick.

I have found an interesting thread about carbon build up and I am currently isolating everything I can with foam to reduce heat loss as much as possible, but I would still appreciate your feedback on engine off times.

Thanks a lot

Tony From West Oz
10th June 2007, 02:13 AM
I do not believe that you can determine this by time. Engine temperature may be better, but IF the carbon build up is due to the oil polymerising on the injector face, while the engine is hot, then it would be best to change back to biodiesel / diesel before any shutdown.
That may or may not be the mechanism for the carbon build up. So you need to do some testing.
For a 5 000km period, starting with cleaned injectors, shut down on biodiesel / diesel at every shutdown. Measure the amount of carbon on the injector faces.
Clean injectors again,
Repeat the exercise using your normal driving procedures. Measure the amount of carbon on the injector faces.
Compare the carbon build up for the different processes to determine whether this is your problem.

I hope this helps,

10th June 2007, 03:57 AM
I think you may be thinking exactly the wrong thing with your 30 minute off too smooth starts.

I used to have a temp gauge in the airbox of a rather powerful V8 I had which proved very difficult to keep cool. I did a lot of work with fresh air intake systems on it. The airbox temp was always at it highest after a short shutdown and eventually dropped many 10's of degrees once the car was moving again and the heat was blown out from under the bonnet.

I believe that your restarts may be smooth because everything under the Bonnet has had time to " heat Sink" and it is highly likely everything is near the ideal temp rather than too cold. This time frame when everything is static in my estimation, is likely letting the oil in the filters, injection lines and pump come up to near ( or right at) the ideal temp and on the restart, everything is running where it should be rather than possibly cooler when the fuel flow through the system may cause a drop in temps combined with the airflow the motion of the vehicle creates.

You will be able to feel the heat build up effect by touching the bonnet before your restarts as against when you first switch off. Even a small engine is a couple of hundred kilos of thermal mass and that dosen't cool too quickly. Your injectors would be at least at normal operating temp and could be fractionaly above due to the coolant being stopped and not being able to carry the heat away from the head at the moment of shutdown.
I would be thinking that the restarts after 30 minutes would be causeing you the least problems of all!

My limited knowledge of Spain is that it dosen't snow there a lot so rapid cooling down probably isn't a big concern. With my own car, I can restart on straight oil with little trouble after 2 hours without even using the glow plugs. With blend, I have done this recently in our winter temps at 6 hours without using the plugs.

To prevent carbon buildup and associated problems, much to the skepticism of many people, I have been running a water injection setup and have no doubt what so ever it has been responsible for the continueing improvement in the way my car runs. I have also had no problems at all with the car despite doing a lot of things that are know No-No's. I have yet to pull out anything for inspection, I'm happy to leave well enough alone, but I do have a change of injectors scheduled so I'll be interested to see how they look when they come out.

I believe like the rest of my car, they have a lot of wear on them and if they come out clean, it would be against the odds and a strong indication the water is doing what I want in preventing any deposits.

If you are interested, you can do a search for the posts relating to this both here and on info pop.

19th June 2007, 03:55 AM
Thanks Tony and David for your comments.

Tony, yes, I guess I need to get a bit more scientific and start with a test plan. I am now finishing a new HE, so right after I fit it I will clean the injectors (I got the operation down to 35 minutes!!) and monitor the carbon build up.

David, your comments about heat building up after shut down are interesting. I didnīt think of it, but now I recall the same happens with braking systems. I am amazed to hear you can restart on WVO after 2 hours shut down without problems. I guess my problem is somewhere else then, probably WVO contamination in my auxiliary tank.
Iīll have a look at that water injection setup in the forum. It sounds good.

By the way, I lived 4 years in Melbourne (what an amazing place that is) and I donīt find Barcelona weather any warmer...