IS300h - Oil on spark plugs

[wookee]

I undertook a DIY spark plug change on my IS300h (122k) a couple weekends ago. Access to each cylinder is dead easy, so if you're a confident DIY'er and you have a  decent torque wrench, I'd definitely give this ago. Lexus will charge you ~£300 for the same job.

The first plug I pulled out looked fine (cylinder 1, closest to front bumper):

There was a bit of carbon build up on the threads, a dry ashy build up around the tips, and a bit of discolouration at the bottom of the ceramic insulation. But I understand this is normal (...?). Otherwise they were dry and healthy-looking, typical for 60k.

Cylinders 2, 3 and 4 though....

... all had a fair amount of oil around the threads, gasket and on the hex nut. Looking in the spark plug wells, I could also see some carbon build up and spots of oil:

Ignition coil plug rubber boots were also quite discoloured, so clearly they have been soaking up oil:

Given the amounts of oil here were fairly low, I decided to continue on with the job and fit the new plugs. Used an extension and clean microfibre cloth to clean up the wells as best I could.

The only other quirk I found was that Lexus Stockport had installed FK20HBR11 instead of the FK20HBR8 factory spec. Having said that, the Denso catalogue suggests these are fine to use in an IS300h. And actually, after speaking to a very helpful Denso rep, I had opted to fit the newer IKBH20TT twin tip plugs, which supposedly outperform the originals, whilst still operating within the same temperature spec. They were also half the price (£27 from Ambush Parts), so this seemed a no-brainer. IKBH20TT looked virtually identical to FK20HBR11, so perhaps they had simply been re-badged. IDK. In any case, I've been running them for several weeks now and they seem great. Seem to be getting a few more MPG now.

Denso recommend installing the plugs dry - so I doubt very much this was Lexus lubricating the threads. Googling around the problem suggests this is a spark plug well / valve cover gasket leak.

Since the car is under extended warranty, I put all this to Lexus Croydon. Their response was that this is normal.

So my question for everyone - is it ok for engine oil to leak in to the spark plug wells? Surely not.

[PCM]

I'm NO expert but I agree - surely not...

I change my lawn mower plug once a year and expect it to come out dry, as it does.

[Mihanicos]

The colour of the spark plug tip tells you a lot about the engine condition and the flame propagation within the cylinders. Light chestnut brown is the ideal colour for stoichiometric combustion. Modern engines tend to run slightly on the lean side on motorway cruising due to cleaning of the oxygen sensors and the higher operating temperature of the combustion chamber. Hence the higher mpg on the motorway around the 70 mph speed. From the photos  your engine is in a very good condition.

Normally there should be no oil on the threads of the spark plugs. In your case it may come from outside due to a valve cover gasket leak or due to lower torque tightening of the spark plugs. I am not sure of your engine configuration or the torque specification of the spark plugs. For my car, as I recall when I changed them, the recommended torque was 19 Nm and there was no oil on the threads.

Chris.

[wookee]

Thanks for the replies.

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From the photos  your engine is in a very good condition.

That's really good to hear!

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In your case it may come from outside due to a valve cover gasket leak or due to lower torque tightening of the spark plugs.

So I did notice that the plug in cylinder 1 (no oil) took a lot more force to undo than cylinder 4 (the one with the most oil). So either the lubricating effect of the oil had helped it come loose over 60k miles, or the engineer at Lexus Stockport (who did the last change) did not torque it down to spec (25nm according to repair manual and Denso catalogue). I find it hard to believe that they would be that sloppy. But who knows.

I had a look in the repair manual and spotted something else a bit surprising. While there definitely are rubber gaskets at the top of the spark plug tubes, it seems there is no gasket at the bottom of the tube. Instead, you're supposed to apply a ring of "Toyota Genuine Adhesive 1324, Three Bond 1324 or equivalent" around the outside and then tap them in to the hole with a hammer until they protrude out by exactly 112mm (!).

So appears to be in contrast to many cars that include the gaskets for the tubes and the valve cover as part of a set, often all attached as one piece. Here's one for a Vauxhall Astra:

 

So... is it possible the adhesive has failed? I can't see replacing that being a particularly fun job. The spark plug tubes also don't seem to be replaceable (can't see a part number on the catalogue for them) so if you damage it, you might have replace the entire cylinder assembly = ££££.

The gaskets at the top are dead easy to replace and cheap, so I could do that anyway. But the tops of the tubes all looked clean and dry, so that seems unlikely to be the source.

Thinking I'll probably inspect again in 6 months and see what it looks like.

If anyone else is changing their spark plugs, I'd be very interested to see if you have the same issue too.