What is it with white block engines and cylinder #4?

Post by **scot850** » 07 Oct 2025, 19:32

I always dread doing the plugs on a Volvo 5 cylinder engine. P80's are not too terrible in NA or turbo form, but P2's are a royal pain as you have to remove the cross pipe to remove the cover.

I've just swapped the plugs (and also the coils) on our son's 2006 XC70. The car is just past the mileage (about 128k miles) for the the scheduled plug swap. It had the first set done at Volvo about 14 years ago at about 6ok miles (96kkm large service).

The reason I dread doing the plugs is not cylinders 1,2,3 and 5. They are straight forward. Every P80 and P2 I have done the plugs on #4 cylinder is a major pain as the plug always gets really tight and I have to work it in and out using a little WD-40 to get the plug out. It has taken me up to an hour to do the one plug successfully as I am paranoid the threads will strip.

So what is it about cylinder #4? Why is always the worst one to remove?

I swapped the plugs and planned to reuse the coils due to the relatively low mileage. However, as usual all the coils had a crack in the body below the boot down to the plastic plug cover tube. I have seen the crack part way, but these were all the way down. They still performed well but I had a new set sitting in a box bought for this car maybe 10 years ago!

Anyone else have this issue and can explain why #4 is a bear?

Neil.

Post by **abscate** » 08 Oct 2025, 01:23

Esteemed colleague. Symbol for 4 is symbol of death

In China, sometimes there is no fourth floor of a building ..

454cid · Post by **454cid** » 08 Oct 2025, 09:20

I've done plugs on my 850 one time, but don't recall an issue with #4. I've got plugs to do it again, so I'll pay closer attention this time around.

Post by **scot850** » 08 Oct 2025, 09:20

Yikes! For me or the car??

Neil.

Post by **850 LPT** » 08 Oct 2025, 11:12

I don't know Neil. I have done quite a few plug changes on white blocks, but never experienced what you are describing.

Post by **matthew1** » 08 Oct 2025, 13:58

Neil I also never noticed anything with #4.

abscate wrote: ↑08 Oct 2025, 01:23 Esteemed colleague. Symbol for 4 is symbol of death

In China, sometimes there is no fourth floor of a building ..

In the US this was often the case with floors and even airliner rows. I've seen both. [EDIT] with the number 13 [/EDIT]

And anytime I get to post a clip from the best movie ever made, based on the best book ever written, I don't hesitate.

The missing floor is in reference to the number 13 being unlucky. This is foreshadowing that Carson Wells will be unlucky.

Post by **scot850** » 08 Oct 2025, 15:00

I think a lot of the issue is the length of time the newer plugs are in the engine between service mileage swaps. In our case for the 06 XC70, the plugs were last swapped in around 2012? With the older cars I swapped the plugs more frequently and in those, after the first set, I didn't have the issue. Difference between regular servicing and overdue catch up servicing.

Neil.

Post by **volvolugnut** » 08 Oct 2025, 15:08

I was going to comment after reading the first post:

"You just need to inspect or change your plugs more often."

But I would never be so crass.

volvolugnutr

Post by **ZionXIX** » 08 Oct 2025, 17:02

I have changed several sets of plugs on p80s and P2s. Ive never had a problem with #4.

Post by **abscate** » 09 Oct 2025, 02:57

It’s one of the reasons I eschew Pt and Ir plugs on my cars. It would take me 20 years to get to 100k on my T4, and so on. Coppers from FreeCP are what I run and the hardest part is keeping track of which plugs are replacements so I stay honest with Scott.

I got to use “ eschew” in a sentence!