Spark plug threads, dry or greased?

[garagestmarien]

Just doing a major service to my 1994 LS400.

My question is, should the new spark plugs be fitted dry, or with greased or oiled threads, or maybe copper slip.

[Tinonline]

Here's the answer: and a note to amend my own experience from the guide I wrote for later LS400 plugs.

I discovered/read a Lexus manual on this and one step is to apply electrolyte grease to the spark plug threads. Next time I will do this.

There was certainly no sign of this on removing my plugs...Lexus service history to the then 72k Miles.

[runsgrateasanut]

As there will always be oil in the pot threads, whether new or existing plugs I don't put anything on them.  The dialectic grease is usually put on the outer part of the lower end of the Spark plug boot  and not near the screw cap on the Spark plug.  That's the way I do it, but others may do differently. Only difficulty is tightening spark plug number one on the early Lexus. Not much room r/h/s front.

 

[jumbojake]

My mate learnt the hard way to NEVER put lubrication on spark plug threads ... it's something people used to do with cast iron heads (copper grease) .. to avoid them rusting in... but with an soft alloy head  it is very easy to strip the threads.... made an easy job very hard, and expensive!

[ColinBarber]

Denso advise not to, NGK say the same:

https://www.denso.com/global/en/products-and-services/automotive-service-parts-and-accessories/plug/basic/torque/

 

Modern plug threads are coated to avoid sticking/corrosion anyway. They are installed dry at the factory, never had an issue removing them.

 

O2 sensors on the other hand, always use the anti-sieze that comes with them on the thread.

[garagestmarien]

Thank you for the replies.

Dry it is.👍

[Tinonline]

Yes - looks like you can do either. Mine went in dry.

If you do use grease, probably best to ensure you use sparingly and only electrolyte grease. 

 

 

[ambermarine]

The issue with applying anything to the threads of spark plugs is the non design factor it as never entered the field of design to do this, so all sorts of factors are introduced outside of the design and use of them.

If it was done in a warranty period the warranty would be voided whatever the  basis of the claim because the insurance company would invoke non design practice .

The possibility of the spark plug insulation separating when extraction is attempted could lead to issues because ot he thermal differences being outside the manufacturers design due to  grease being present and subsequent locking up,Loctite is designed to lock up the threads by solidifying, baked grease as a similar effect.

Some times we tend to over think the requirements of components and their operation with regards to the spark plug just screw it in and leave it to do its job.

[steve2006]

I did mine recently and my tip is to get a short piece of rubber hose which fits over the nipple connection of the plug, lower the plug in and twist the rubber hose to start the threading as this prevents possible cross threading. Pull off the hose and use a plug socket with a torque wrench to fully tighten.

[Razor61]

Dry is the way to go as designed, I have never ever applied any form of grease, oil or anything else to the threads when changing spark plugs. If the existing spark plugs come out ok then the new ones will go in ok without any help. Put new plugs in using finger pressure then torque up, I’ve never heard of anyone stripping threads using finger pressure..........

[MLW]

According to Denso: Denso Spark plugs torque = 22 Nm dry

[plexus914]

LS400 1990 - 1994

Plugs torque: 18Nm

 

LS400 2000

Plugs torque: 17.5Nm        

No mentioning of any sort of grease when reinstalling spark plugs.

 

PS:

- Remove spark plugs on an alloy engine only when engine is cooled down.

- Do not use anti-seize on spark plugs. Put them dry back in.

 

[garagestmarien]

Here is an update.

The engine full service is done and everything is good. It starts and run perfect.

Now I have moved onto the gearbox to do an oil and filter change.

Drained the sump and removed it. Very minor amount of metal dust on the magnets, which I guess is normal for a 26 year old gearbox.

However, on one of the magnets I found the screw in the photo. (12mm x 4mm).

The gearbox has never given any problems, my reason for service, is just that I am keeping the car and want to make sure everything is good.

I am a bit alarmed, where this screw has come from. I plan to have a good look at the valve body before I fit the new filter, but wonder if by any chance, anyone on here, recognises it.

[rich1068]

Yikes!

[garagestmarien]

Problem solved.

Goes here, but no idea what it does or what it is for. But fitted and tight.

[rich1068]

Double yikes!

[garagestmarien]

Now I have the gearbox on my 1994 LS400 serviced.

Changed oil (Sump drain and removal), fitted new filter, cleaned everything up and reassembled.

I bought 2 liters of Type iV, but this has not made an impression on the dipstick.

There are no leaks, but of course I removed the radiator when I did the timing belt, so lost an amount of transmission oil from the cooler. So more oil on order.

Now, Question,

The oil that came out of my gearbox was close to black and although it did not smell burnt, it did smell bad.

I have seen in the past that there is an idea to drain and refill the sump a few times to get more new fluid more into the box than old.

My question is, how many times should this be done. 2 times, 4 times ?

[rich1068]

Different car but I did just that for my GS300. In fact I did it on my Volvo V70 too. It's easy enough because you barely have to lift the car if at all. With the correct bar and socket you can reach the gearbox sump just lying by the car. I think on the GS I did it about 5 times, can't remember exactly but I got through 2 or 3 5ltrs of fluid and roughly 2 litres came out each time. There are some tables floating about that calculate how much old fluid is left after each time 2 litres is removed. I'll have a scout round.

Tip: buy another sump plug. Removing mine that many times it did start to mis-thread.