Coolant leak in spark plug well

Ubwa · November 25, 2021

Hi everyone.

My RC-F went to the dealer for its "cheap" 6-year service today. When it came to changing the spark plugs, I was called in to be shown the rearmost passenger side spark plug well full of coolant. I am wondering if anyone else has experienced this?

The car runs fine, the coolant was clean, no oil residue in coolant or cap etc, and the level in the reservoir was fine, I checked it a couple weeks ago when refilling the windscreen washer fluid and the technician confirmed it was ok to prior to him draining.

So far, they have been diagnosing the cause since 13:00'ish today and still can't give me a reason, and are now talking of the engine having to come out etc., which seems weird to me as if it was that big of an issue there would be other signs.

It has full Lexus service history too so has been looked after.

4969_LXS · November 25, 2021

That's a rather strange scenario.

From a cross section of the cylinder head, is that a coolant passage by the spark plug tunnel, might be a crack there?

I've never known an engine push coolant past the spark plug if the head gasket has failed from my experience. Never know though, but I'd of thought you'd experience very rough running before this was found and a CEL for misfire.

I wouldn't of thought the engine would need to come out for diagnosis. The logical step from my view, would be to remove the coil pack, soak up all the coolant and let the engine idle from cold to warm, maybe light revs to increase flow and see if it fills up again, if so, from where. Might be for some strange reason, it got in there by accident, maybe someone tripped or lurched with an open coolant bottle and it spilled in there during a service, would be mad though.

It shouldn't need to come out to take the head off if it's like the ISF. Once you remove the airbox, there's plenty of space to remove the timing chain cover first then remove the head to investigate.

Any other suggestions fellow F'ers ?

BillNick · November 26, 2021

Hmmm very weird.

Only explanation really is a crack in the water jacket....

Wonder if valley plate issue could be related??

Ubwa · November 30, 2021

Well as suggested above, it is a crack in the head. So it needs a new head. Dealer is trying to sort something out with Lexus as it must have been a latent defect from new.

hockeyedwards · November 30, 2021

On 11/26/2021 at 2:02 PM, BillNick said:

Hmmm very weird.

Only explanation really is a crack in the water jacket....

Wonder if valley plate issue could be related??

Wasn't the valley plate 'issue' a US only and IS F not RC F problem?

4969_LXS · November 30, 2021

@Ubwa That's the first I've ever heard of a 2UR-GSE to suffer a cracked head. I'd of thought with full Lexus service history it would be covered under the Lexus relax warranty.

@hockeyedwards I recall seeing a thread on Community F Facebook group or clublexus that a GS F has suffered a valley plate leak state side. Will need more research to verify though

BillNick · November 30, 2021

2 hours ago, hockeyedwards said:

Wasn't the valley plate 'issue' a US only and IS F not RC F problem?

Seen quite a few for RCF unfortunately

Ubwa · November 30, 2021

1 hour ago, 4969_LXS said:

@Ubwa That's the first I've ever heard of a 2UR-GSE to suffer a cracked head. I'd of thought with full Lexus service history it would be covered under the Lexus relax warranty.

This is the first year of the lexus relax warranty being available, after the service which identified the issue...

I did try buy a Lexus warranty like I did for my IS-F when I purchased the car in July to be told its not available anymore and told "not to worry, you will get the new Lexus relax warranty when it comes in for its service" - which is as useful as a chocolate teapot at this point in time.

Barry14UK · December 1, 2021

Unless Lexus are prepared to make a generous contribution to replace head, together with labour this is likely to be expensive. In the old days is was sometimes possible to specialist weld cracked heads but possibly this can't be done here.

hockeyedwards · December 1, 2021

12 hours ago, 4969_LXS said:

I recall seeing a thread on Community F Facebook group or clublexus that a GS F has suffered a valley plate leak state side. Will need more research to verify though

Noooooooo

12 hours ago, BillNick said:

Seen quite a few for RCF unfortunately

Double nooooooo

Ubwa · December 1, 2021

Will gladly have had that rather than the current problem from what I understand it to be…

BillNick · December 1, 2021

Best of luck with the warranty claim, will be very surprised if its not honored.

4969_LXS · December 1, 2021

To echo @BillNick I'd be surprised if it isn't covered by warranty.

To hear RCF's are affect by the valley plate as well, indicates to me that LC500's will suffer the same issue.

Pielight · December 5, 2021

On 12/1/2021 at 9:59 AM, hockeyedwards said:

Noooooooo

Double nooooooo

+1😱 Maybe not so ‘bulletproof’ then.

Pielight · December 5, 2021

I wonder if that crack could have been caused by over tightening the spark plug? It seems unlikely but it’s possible and would explain it being a one off, if indeed it is.

Ubwa · December 7, 2021

Have to go radio silent on this for now - will update when able to

ColinBarber · December 7, 2021

On 12/5/2021 at 11:00 AM, Pielight said:

I wonder if that crack could have been caused by over tightening the spark plug? It seems unlikely but it’s possible and would explain it being a one off, if indeed it is.

You would normally expect the thread to be stripped on an aluminium head before other damage was done but who knows. Hopefully whatever the issue is it's a one-off.

Pielight · December 8, 2021

On 12/7/2021 at 8:47 PM, ColinBarber said:

You would normally expect the thread to be stripped on an aluminium head before other damage was done but who knows. Hopefully whatever the issue is it's a one-off.

Yes I did consider that the threads are the weakpoint but thought that it could be possible that the plug was very tight stressing the area but didn't strip, then when heated with expansion and movement the stressed area cracked. There does not seem to be a lot of material around the threads. This is maybe my wishful thinking to categorise it as a one off!

ColinBarber · December 9, 2021

12 hours ago, Pielight said:

This is maybe my wishful thinking to categorise it as a one off!

Hopefully a one off. RC F and GS F were mechanically bulletproof on these forums, now we have had one transmission failure and one engine/head failure 😬

ubersonic · December 12, 2021

On 12/1/2021 at 5:33 PM, 4969_LXS said:

To hear RCF's are affect by the valley plate as well, indicates to me that LC500's will suffer the same issue.

This has been known for some time, the valley plate design aspect that causes the issue was never changed for the LC500/RCF/GSF, hopefully it's revised on the IS500 lol.

Duggie B · December 12, 2021

1 hour ago, ubersonic said:

This has been known for some time, the valley plate design aspect that causes the issue was never changed for the LC500/RCF/GSF, hopefully it's revised on the IS500 lol.

If this is a known design flaw then it will be a manufacturing issue and I imagine covered under the relax warranty 🤞

Ubwa · December 13, 2021

Only if it breaks within the warranty period, if it happens in the no mans land of warranty expiring and first service with relax…

Ubwa · February 13, 2022

Thought I would update this. Had the car back a week, all ad good as new. Had to have the engine pulled and the left hand head replaced. Unfortunately not quite "overnight parts from Japan", but at least I go there in the end.

I can't speak highly enough to the service I received from Lexus cheltenham, and Toyota GB who made it somewhat less painful for me.