My renault megane scenic 1.9dci today I was going to change up a gear on my car and the engine reved

when I went to put in the cluch the engine reved right up to 5000 reves and lots of brow clear smoke came out what could be the problem I had a mechanic out he says it looks like it has already had a turbo so its not tht unless it is faulty
shaun11
Asked Sep 06, 2012
I don't understand what is "brow clear smoke?"

When you put in the clutch on an engine under a load, that takes the load off and it would be normal for it to increase the RPMs if you don't back off the accelerator at the same time.

An engine with bad piston rings will blow smoke when the load changes because the slack lets oil get past the defective rings and burns it in the combustion process. If you have to keep adding oil, that could be what's going on but smoke from burning oil is normally black or dark gray.
Rob
Answered Sep 06, 2012
Edited Sep 06, 2012
yeah I dont undestand it just reved up its self what do u think I should try
shaun11 Sep 07, 2012
If it increased the RPMs when you put in the clutch, it didn't do it by itself. If you are going up a hill (the engine is under a load) and you leave your foot on the accelerator without backing it off and put the clutch in, it will do what you describe because the clutch takes away the load. If it's increasing RPMs on its own when out of gear and no changes in the accelerator petal, it could be something blocking the air supply and choking it, trash in the gas line that randomly opens up or the turbo. Not all turbos work the same. some operate over the whole range of RPM while others only kick in when it requires extra power. If you have added or replaced the turbo with anything other than the stock turbo for that vehicle, you need to have a specialist for that make and model look at it.

Rob Sep 07, 2012
Shaun, your Turbo has most likely blown. There is a design fault on the Renault 1.9 DCi engine and when a turbo blows, it causes damage to the engine, resulting in engine blow by (compression gasses escape past the piston rings into the oil sump and contaminate the oil) this results in excessive oil consumption and insufficient lubrication of the turbo which results in early turbo failure of the replacement turbo.

The worst part of this is that a valve on the engine (EGI valve) which returns unburned fuel back into the system is known to stick initially, and cause turbo failure.

Once the turbo goes, the entire engine needs to be redone with new piston rings, especially when you have engine runaway as you have described.

Best bet is sell the piece of junk and NEVER buy another Renault.

SDY245
Answered Jan 17, 2013

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