Can diesel on the outside of the engine combust?

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GrumpyGel

GrumpyGel

Well-Known Member
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Christchurch, New Zealand
My leak back pipes went in the week. First noticed something was up when steam/smoke started coming out from under the bonnet - I presume it was diesel vapourising.

I've fixed the pipes and taken it for a run getting it up to temp. When I stopped and lifted the bonnect there was some smoke/steam floating around the engine bay - which I presume is the residue diesel vaporising.

Was I foolish to run it up to temp with diesel laying no the engine?

With the engine hot, will diesel ignite and cause an engine bay fire?
 
Keep in mind you can drop a match or several in Diesel and it wont ignite, however if you get it up to a warm temperature and then drop a match in BOOM !

I have leaked Diesel a fair few times from filters etc and just let it evaporate.

Its dangerous.... think about a glow plug.. there is no spark just heat and compression. I suspect you may struggle to get ignition or compression outside of the cylinder but I wouldn't risk it.
 
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it's technically possible.... but an L series doesn't have any external parts hot enough to ignite diesel.


If it does - mine would've gone up in flames in the first week, when an injector union decided it didn't want to seal. Literally sprayed a couple of litres of diesel all over the engine bay, after the 30 mile commute home. I thought it smelt a bit funky, so checked, and the entire engine bay was drenched in diesel. The little "dip" in between the EGR and main intake charge pipe was filled with diesel.

Dried up fairly quickly however, and made the engine bay look cleaner too :lol:

 
Did once pick up the smell of diesel coming thro the air vents when travelling on m25, diesel smell got stronger as I was getting closer to the source which turned out to be an artic travelling in lane one with all manner of fumes, mist spray coming out from under cab, whilst overtaking and trying to attract the drivers attention the fu..... Jg thing just burst into flames, so we all stopped and driver got out safely, but never again will I leave diesel on surfaces which get hot.
 
So it probably won't catch fire, and I've heard of bad news from people getting enthusiastic with a jet washer and ruining tensioners (bearings) etc. But I think I'll give it a bit of a clean tomorrow.

Thanks for the input.
 
Flash point of diesel is 52 C, which means the minimum temp at which it can start to form a combustible vapour. However, the fire point is 256 C, i.e. the temp at which it can autoignite. The only place on the engine that reaches the latter temp is the exhaust (excluding oddities like the fuel burning heater).

Hence: diesel on engine = OK (think how many old tractors there are festooned with diesel leaks).

Diesel on exhaust = danger.
 
manifold_danger.jpg
 
Like the cat mechanic at work. :hysterically_laughi:hysterically_laughi:
 
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let it get on a hot turbo, and watch a good fire. Make sure you have a dry powder fire extinguisher handy.

Had it happen on a mack truck once. Saw a little smoke coming from the hood, slowed down on a side road to look and when I stopped, well very glad I had the fire extinguisher, saved the truck. It had a leaky injector line.
 
guineafowl21 said:
Flash point of diesel is 52 C, which means the minimum temp at which it can start to form a combustible vapour. However, the fire point is 256 C, i.e. the temp at which it can autoignite. The only place on the engine that reaches the latter temp is the exhaust (excluding oddities like the fuel burning heater).

Hence: diesel on engine = OK (think how many old tractors there are festooned with diesel leaks).

Diesel on exhaust = danger.
Click to expand...

Phew its a good job the exhaust isn't below the engine where any diesel would run to... dangerous advice... Tractors always exhaust side not below.
 
ER1C said:
Phew its a good job the exhaust isn't below the engine where any diesel would run to... dangerous advice... Tractors always exhaust side not below.
Click to expand...

There are a few exceptions, mainly for orchard work and suchlike. But pretty much you are right, the exhausts go up. :)

And I agree diesel leaks on a tractor are dangerous. Tractors often have a lot of dead vegetable matter on them, from topping and so on. And when diesel has something to soak into, and act as a wick, it burns very well even at low temperatures.

Personally I would always repair any leaks asap.
 
ER1C said:
Phew its a good job the exhaust isn't below the engine where any diesel would run to... dangerous advice... Tractors always exhaust side not below.
Click to expand...

Yes, I didn't mean diesel leaks are ever safe, just that engines don't get hot enough to ignite the fuel. Of course, engines generally have exhausts, so ....
 
diesel can be set fire to believe me, many years ago when the miners strike was on a miner was going to work and was breaching the strikers line so one of these miners took revenge he knew where he lived ,so he went round at the night time when the miner was at work ,he got a spray bottle and sprayed diesel through the letter box while holding a light to it the house was burnt down, the one thing he did not count on was the miners wife was in there and died.
 
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A lot of stuff will ignite very quickly and disastrously if its in a fine mist/dust!

I thought this worth a thread by itself. Its still smoking when hot even after jetwashing so I'll put the ongoing saga back on the original leak back pipe problem thread.
 
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