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Missfire, oil and mayonnaise on plugs, s**t!

  Clio 182
Hi guys,

Car started misfiring on me yesterday, never done it before, very down on power, not sure if was running on 2 or 3 cylinders but pretty rough anyway. Idle wasn't bad though, but a bit jumpy. Smell coming out the back was awful (bad eggs), I guess due to the cat being dowsed in fuel, and looked a bit more steamy out the back.

Had the AA out, he checked sparks on coil pack, all very strong. Had a look down plug wells, they were dry, but he sprayed them with WD40 anyway, didn't make any difference. He suggested plugs, then leads, then coil pack. He's known coil packs spark well, but be out on timing.

This happened on Thursday night, but I had cleaned the engine bay over weekend with a fair bit of water, so was worried it might be that. Had the ECU out this morning and left it somewhere warm all day in case it was wet.

Had Denso plugs in, so I changed them for the NGK's today, hoping that might be it. But had a nasty surprise and not sure how serious it is. Plug 1 was dowsed in fuel, Plug 2 had quite a bit of oil on it, Plug 3 had quite a bit of mayonnaise (looked very like water/oil mixture) on it, and Plug 4 also dowsed on fuel.

Now worried it might be early signs of head gasket! It's a 182, 70k miles which would be a bit surprising. It is using oil, probably about a litre in 2000 miles and can't find a leak. But no mayonnaise in filler cap or dipstick and no oil in water. Anyone else had this?

Got some new HT leads arriving tomorrow, so when doing them will do a compression test too to find out more and see what happens, but any thoughts welcome!

Bloody french cars!
  Clio 182
I've done the compression test, but not sure if it means anything, so any help appreciated here:

Cylinder 1 - 11.8bar
Cylinder 2 - 11.2bar (this one has oil in it!)
Cylinder 3 - 11.0bar (this one has mayonnaise in it!)
Cylinder 4 - 11.3bar

What sort of variation should I be expecting? And what is the compression ratio on these 2.0 16V engines?

Don't know if this is all that conclusive, but I'm still fearing head gasket.

Other thing is after checking this it ran like crap, maybe because I connected the HT leads wrong. Is this correct, cylinder no. 1 at gearbox end (right as you look in engine bay) and no.4 at belts end?

Then on coil, kinda looks like (again as looking in bay):

I think I did back right as 1, back left as 2, front right as 3 and front left as 4, is that right?!

  Clio 200 Cup
Almost certainly head gasket failure.

If it was just oil in one cylinder then MAYBE a valve stem seal + something funny happened to a valve guide. Or a piston ring issue.

However, you've got mayo aswell which tells me you've probably got cooland mixing with oil - so I'd put my money on it being the head gasket.

The presence of oil in the cylinders will "help" the instantanious compression figures, but you might get a different picture from a proper leakdown test as this will flag up sustained leakage.

Either way, I'd be taking the head off.


  RB 182 cup
those compression figures dont seem to bad to me there all close enough to each other

plus if there if oi/water in the bore i would expect it to smoke a lot

is it still missfiring?? if not i would clean the plugs put them back in then go for a run and then take the out again then if poss post up some pics of each plug
  Clio 197
If your engine has ever been 'cleaned', you'll find that water sits in the plug seats permanently...

...which might be the problem. A a good cleanup (with a suction tube), then new plugs should sort it IMO.


ClioSport Moderator
  Whichever has fuel
I'd be very very suprised if it was headgasket failure. Thats not something these engines do believe it or not!

I'd personally remove all the plugs, clean it all up fit new plugs/leads (All genuine Renault items!) and I reckon you will be sorted.
  53 Clio's & counting
I would lay a big bet not headgasket

I think it has come from cleaning the engine, have seen the same simptoms as you before on various 1*2s

As Dan has said, get the plugs out, change them, and possibly the leads, depending if they are contaminated, i think waters got down in the plug holes, probably with a bit of oil from a weeping rocker cover, seen this a few times too, causes a funny mixture, the smell would be coming from the over fuelling caused by the missfire where you have a cylinder not firing.

Those compressions seem about right, and if it was fine before the engine cleani think sorting the above will solve the problem
if it's nothing serious, it might also be an idea to renew the oil and filter, as they may be contaminated with fuel if you've been running without a spark in one or more cylinders
  Dodgy one
I would lay a big bet not headgasket

I think it has come from cleaning the engine, have seen the same simptoms as you before on various 1*2s
I can agree with that, I was going to post last night but i couldnt type correctly so gave up lol, Lots of beer FTMFW lol

Everyone seems to have posted what i was going to put but i'l add your readings should be within 10% of each other which when converted to PSI seem to be :)

You connected the plug leads correctly too #1 is at the flywheel end
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  Clio 182
Thanks for help guys, I won't assume the worst just yet then.

I've just put new plugs in, and should have some new leads waiting for me at work when I get in tomorrow, so I'll see what that does.

It started missfiring on the Thursday after cleaning the engine at the weekend, so that's a fair delay for it to start playing up. The plug recesses seemed pretty dry to be honest, bit of condensation in no.1 but that was about it. No oil down the recesses either, can't see any leaks from the top cover.

Been looking through previous reciepts which came when I bought the car (in June this year) and it seems it had a new water pump and timing belt at 60k. If the water pump had failed, it could mean the head got hot before which could lead to the head gasket failure...
  53 Clio's & counting
Yes thats true, it could have,but the water pump could have been changed as a precausion, does it say anywhere in your reciepts mate?
  53 Clio's & counting
depends on a lot of things, some cars overheat easily, some cooling systems are not up to scratch, some have poor cooling tracks through the cylinder head, there are a lot of variables to take into context
  Clio 182
Got the new HT leads on today, and it seems to be running good again. :cool:

Bought them from, as they are way cheaper than OEM, however they seem to have sent me the wrong type as the rubber extension has a 10 degree bend in it, so doesn't make a good seal at the top of the plug recess. At least they work as HT leads though!

Gonna give it a bit of a run and then have a look at the plugs again to see if I've still got any oil / mayonnaise, will post up some pics. Reading on here, sounds like valve stem seal might be the other culprit if head gasket is in tact.

I had connected leads up wrong after doing compression test, hence it getting worse, luckily the coil is numbered which I hadn't noticed before!

Also noticed my water level is pretty near min, but not sure where it was before as I've not really taken any notice of it before as it was above min, so will keep an eye on that.

Panic over... for now at least!
  RS CLIO 197
may be worth mentioning - exactly how do you get oily mayoniase on the plug when its in the combustion chamber - if the head gasket has gone as said then the mayo would be visible on the dipstick/oil filler cap - not the plug !!

compressions are good and even - so it uses a bit of oil - just check it regularly - as for losing water might not be head gasket - could be a hose etc

just dont jump to conclusions so fast as it could cost time and money