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Discussion Starter #1
Hello..
Last Wednesday my mazda 6 57 plate diesel decided to have a hissy fit when the engine started to rev uncontrollably to the max.
I knew it was overdue an oil change and the levels were high but hey ho...Just didn't have the time but anyway, it revved for about 5 seconds then dropped to normal (it did this when I dropped the clutch to change to 4th)
Within a few seconds I felt the car wanting to accelerate without much throttle so dropped the clutch again and boom, off the scale again but didn't return to normal. This went on for about 5-10 seconds then I decided to turn the ignition off and coast to the inside lane. Now, the engine stopped ok...No overrun...Just cut as normal...I got recovered and have changed the oil today...I'm scared to start it. It'll need jumping anyway but would anyone know if it's safe all things considered.
I've read loads on this and I'm hoping the now new oil and level will rectify the problem..
A whole washing up bowl of oil was drained!
Please...Any advice on restarting it up now.
Cheers in advance..
 

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Hello..
Last Wednesday my mazda 6 57 plate diesel decided to have a hissy fit when the engine started to rev uncontrollably to the max.
I knew it was overdue an oil change and the levels were high but hey ho...Just didn't have the time but anyway, it revved for about 5 seconds then dropped to normal (it did this when I dropped the clutch to change to 4th)
Within a few seconds I felt the car wanting to accelerate without much throttle so dropped the clutch again and boom, off the scale again but didn't return to normal. This went on for about 5-10 seconds then I decided to turn the ignition off and coast to the inside lane. Now, the engine stopped ok...No overrun...Just cut as normal...I got recovered and have changed the oil today...I'm scared to start it. It'll need jumping anyway but would anyone know if it's safe all things considered.
I've read loads on this and I'm hoping the now new oil and level will rectify the problem..
A whole washing up bowl of oil was drained!
Please...Any advice on restarting it up now.
Cheers in advance..
I would take the air inlet to the throttle body off exposing the butterfly and then turn the key to on/run but don't try to start it. Look to see how the butterfly is. If it's all the way open, I would not start the car. I've never heard of a vehicle over revving due to oil.
 
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Discussion Starter #3
I would take the air inlet to the throttle body off exposing the butterfly and then turn the key to on/run but don't try to start it. Look to see how the butterfly is. If it's all the way open, I would not start the car. I've never heard of a vehicle over revving due to oil.
 

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Discussion Starter #5
It's a common fault with Mazda diesels apparently...Due to the dpf regen thingy. I've been travelling up to Coventry from London a lot this summer so no problem with regen but these last 2 months I've only been tootling around town...
Thanks for your response by the way.
My throttle body is not accessible unless I strip half of the engine down..
 
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The thing you mentioned with the oil level rising is actually due to fuel dilution. I've made a whole thread regarding this issue with tons of useful information which I can link if youd like to read it. Basically speaking, do you do a lot of short distance trips? When the engine doesnt get a chance to fully warm up gasoline (well, in your case diesel) diluted the engine oil supply. It's a fairly serious issue but there are simple ways to deal with it such as driving longer distances and using oils with additives specifically formulated to fight fuel dilution.

However, this has nothing to do with your engine revving on it's own. Completely unrelated issue.
 
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Discussion Starter #9

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Discussion Starter #10
Update...
I took over 11 liters of oil out of the sump and obviously changed it with the correct amount...Been running around for over a month now and runs like a dream...As it always has to be honest.
Initially there was a fair amount of smoke from the exhaust and was a bit worried but it has long since gone. I assumed at the time it was the breathers that were just clearing out etc and seems I assumed right.
So oil dilution is common for mazda diesels...Just keep an eye on that dipstick.
 

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11 liters?!

Uh, you have a serious problem. Find it or you're going to lose that engine.

I'll lay odds you have one or more leaking injectors. No, this is NOT normal.

BTW if you didn't find the low points in the charge air circuit (e.g. pipes going into the intecooler, etc), drop them and drain whatever is in there out. There may be a fair bit of oil in there as well.

The risk isn't just of a runaway - diesels have very little room in the combustion chamber when the piston is all the way up and you can have a hydrolock with that fluid -- which will lift the head, bend or break rods -- or both.
 
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