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My mechanic has recommended that I fix an oil leak in my car.

My car is old and really, I rarely drive it so I'm reluctant to spend any money on fixing it unless it's going to cost more later on or if it's going to be dangerous.

With the oil leak, the mechanic says that the oil leak is leaking out the engine and onto the exhaust and could potentially start a fire.

Just wondering, is this a real possibility or is the mechanic just being a little alarmist to try to get me to pay a little bit more?

If it is a possibility, is it one of those things where I'll be driving down the road and all of a sudden, my bonnet will be on fire or is it more likely to smoke first and i would have time to get out of the car first etc.

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How big of a leak are we talking about here? How often do you have to add oil? –  Mark Johnson Sep 11 '13 at 1:04
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3 Answers

It is entirely possible. Here is one of many videos on YouTube.

car on fire

Unfortunately, it is impossible to predict how much time or warning you will have before a car fire can occur. If you don't have the money to fix it now you should at least make certain that oil isn't allowed to drip directly onto the exhaust. I know the video may seem like the extreme possibility but, that is what you should keep in mind when dealing with flammable fluids and materials.


EDIT

Adam Wallace at voices.yahoo.com...

If oil leaks on your exhaust, it can be dangerous. The buildup of oil on your exhaust can potentially cause a fire. A car fire is something that nobody wants.

Charles C. Roberts, Jr., Ph.D., P.E. at croberts.com...

  • Volkswagen

    Burn patterns indicate that the cap was not on the oil filler neck at the time of the fire. Crankcase pressure expelled oil out of the filler neck onto hot exhaust components, causing the fire.

  • Unnamed Vehichle

    ...caught fire shortly after leaving a service station, after an oil change. Engine oil had been blown out of the oil filler neck onto hot engine components, causing the fire.

  • Pick-up Truck and Transmission Oil

    ...A fire developed under the transmission boot area while the vehicle was towing a heavy load, which was within the capability of the vehicle. Figure 5 is a view under the vehicle with an arrow pointing to a transmission oil cooler tube fitting that apparently leaked transmission fluid, which then sprayed all over the undercarriage of the vehicle. The transmission oil sprayed onto the exhaust pipe, causing a fire in the vicinity of the transmission oil leak.

Evelrod at eng-tips.com...

If the leak is big enough it can burn that sucker to the ground! (Been there , done that. 350 Chevy C-250, summer ,1981)

Debbie Murphy/autoMedia.com on mobiloil.com...

...check for oil leaks and always use a funnel when adding oil. Oil spilled on a hot exhaust manifold can cause a fire.

If you have a gas station attendant add oil, double check that the cap is on securely. This sounds obvious, but better to check than end up with oil all over your engine compartment at best, or an engine fire at worst.

Burning car

Another video on youtube.com

video of car fire

The flash point of Mobile 1 10w30 motor oil is 232 Deg. C. according to its data sheet.

Exhaust gas temperatures can range widely depending on the car. An average I've found mentioned is 149 Deg. C. at idle to 760 Deg. C. at high load and rare extremes of 1200 Deg. C. Below is a quote by "the solitaire"from sportscarforums.com

EGT (exhaust gas temperature) can easily range between 300 degrees F at idle and 1400 degrees F at high load.

The 232 Deg. flash point of motor oil easily falls within the range of exhaust gas temperature.

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A bunch of pictures without context and other people's opinions don't really qualify as evidence. I'm open to hearing another side to this issue, but I think it should be supported by documented facts and reasoning, rather than sensationalism. –  R.. Sep 10 '13 at 5:25
    
@R.. Charles C. Roberts, Jr., Ph.D., P.E. is hardly interested in sensationalism. He's a professional in accident reconstruction and investigation. Admittedly, I did make some references to people with original claims but, I also peppered my post with plenty of respected sources. I wasn't completely finished editing when you made your comment. I've also added a data sheet on 10w30. Wikipedia says "reducing its tendency to burn". It does not say that it does not or will not ignite, only that a low flash point is desirable. The pictures are links to the context except for the quoted image. –  Seminecis Sep 10 '13 at 5:43
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I think you need a fairly significant amount of oil to come in contact with the exhaust to start a fire. How dangerous is the occasional drip? –  Mark Johnson Sep 11 '13 at 5:37
    
@MarkJohnson I agree. Even if a single drip ignites it won't sustain a fire. Realistically it is the buildup of a slow drip over time that could cause issues. I've read buildup being cited as cause of fires but, I'm not sure how quickly oil builds up. I think the two situations to avoid would be a fast leak onto the exhaust and a slow leak onto the exhaust on a car that sits long enough for buildup to occur. I think a slow drip onto the exhaust on a car that is driven daily would burn away without causing a fire. –  Seminecis Sep 11 '13 at 8:54
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Indeed, an oil leak in a hot area is a car fire waiting to happen. Example: https://en.wikipedia.org/wiki/Pontiac_Fiero#Engine_fire_reputation

"...oil to escape and come into contact with engine parts. The oil would catch fire when it contacted the exhaust manifold or hot exhaust components..."

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That sounds like the fires resulted from a large amount of leaking oil. –  Mark Johnson Sep 11 '13 at 5:33
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Engine oil starts to evaporate at around 400F (200C). The fumes are then flammable so if the oil is built up on some hot parts of the vehicle it could be dangerous.

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