The engine in the old bus isnt the healthiest. It leaks every fluid imaginable, but runs acceptably well that it just sort of gets ignored and soldiers on.

Its always started missing a few cylinders, but they all seem to come alive after a few seconds and a bit of RPM.

It leaks coolant from various places, and i so slightly suspect a headgasket issue as it seems to pressurise the hoses pretty quickly (and they often stay pressurised) but it doesnt over heat and will do hundreds of miles without issue. Its always been like that since i've had it. Again, works well enough that i dont want to start fiddling.

Cylinder 8 also always fouls its spark plugs, they end up crusted with oily deposits.

So thats the background. Last week i was taking an old car to the scrap man, so she was pulling probably 2 tonnes of trailer. It felt a bit flat, but i wasnt really beating on it and just taking it easy trundling up the duallie at 50. However once i got to the yard (about 5 miles away) it was clear it was idling dog rough. RPMs were down below 500, and it sounded like crap. Revving it, it sounded like an old aircooled beetle. Clearly some cylinders not happy.

Got offloaded and drove home and it was clearly unhappy, missfiring badly at low rpm pulling away and down on power. I knew i had some spark plugs on the shelf so i decided to change them. Unfortunately what i actually had was 3 new plugs, and 5 used ones (no idea!). So i installed the new plugs in cylinders 8, 6 and 4, figuring it might be the fouled plug that was causing issues, and gave it a try. Still missfiring as bad as ever so i gave up and ordered 5 new plugs.

Plugs came today, so i swapped the remaining 5 out, and went for a test drive... And its fixed. Hurray? I dont know. The plugs that came out looked perfectly serviceable, so currently i have no idea wether its just a coincidence or the problem is actually sorted. I guess some more miles needed to tell.

However, i noticed that theres vast differences between the plugs in terms of the deposits, so i took some photos:

Starting with bank 2, plugs 4 and 6 look ok i think? 8 is obviously fouled, but then 2 is very strange, pale and minimal deposits.
Moving to bank 1, plugs 1 and 3 have odd orange coloration to their ceramic insulators, perhaps a touch rich? 1 also has weird deposits or maybe corrosion around the base of the plug thread? 5 is almost normal? 7 looks lean/hot, perhaps a bit like 2 from the other bank.

Any thoughts would be appreciated. None of these plugs look bad enough to cause a missfire, with the exception of 8, but swapping that out didnt fix it. The varying plug condition also makes me wonder whats going on here.

Orange colouration on the plugs is usually a sign that you are burning coolant, which the rusty ends to the base of the plugs would seem to confirm. The oily plug from number 8 would suggest oil getting in there so likely to be valve stem seals. Sounds like a top end refresh is on the cards in a while. The plugs look to be the BKR6E with the smaller hex that would normally only be fitted in the later Thor engine, for an early car you want to be running NGK BPR6ES plugs.

Plug choice does make quite a difference. I worked on one a car few months ago that simply wouldn't start. It would fire sometimes but would also backfire down the exhaust suggesting timing. We spent ages checking (and changing) the crank position sensor and making sure the tags on the flywheel were all there and not bent and the output from it was good and that all the HT leads were in the correct place. Even though it had a brand new set of plugs in it I ended up taking one out to find it was a Denso. Owner had been recommended these by an 'expert' on facebook so had fitted a full set. Pulled them out, fitted NKGs and it fired up first turn of the key.

The plugs with the smaller hex are BCPR6ES - same as the BPR6ES

BKR's must be something different altogether

BKR6E are basically the same as BCPR6ES

NGK say the only difference between K and CP is that the whole plug is slightly shorter. K is the newer "ISO" version of CP:

My Audis use BKR6E so i tend to have them on hand, and the smaller hex makes them easier to get in and out.

Ahh, interesting to know! In that case they should be fairly interchangeable... I use the BCPR6ES on mine - again, because the smaller hex is easier to work with!

Gilbertd wrote:

Orange colouration on the plugs is usually a sign that you are burning coolant, which the rusty ends to the base of the plugs would seem to confirm. The oily plug from number 8 would suggest oil getting in there so likely to be valve stem seals. Sounds like a top end refresh is on the cards in a while. The plugs look to be the BKR6E with the smaller hex that would normally only be fitted in the later Thor engine, for an early car you want to be running NGK BPR6ES plugs.

Plug choice does make quite a difference. I worked on one a car few months ago that simply wouldn't start. It would fire sometimes but would also backfire down the exhaust suggesting timing. We spent ages checking (and changing) the crank position sensor and making sure the tags on the flywheel were all there and not bent and the output from it was good and that all the HT leads were in the correct place. Even though it had a brand new set of plugs in it I ended up taking one out to find it was a Denso. Owner had been recommended these by an 'expert' on facebook so had fitted a full set. Pulled them out, fitted NKGs and it fired up first turn of the key.

Yeah the orange puzzled me. I had a google and folk were suggesting "fuel additives", but i guess coolant might well make sense, especially when we add in what looks like rust on the plug. I've suspected a gasket for a while, but it never overheats. Coolant disappears at a fair old rate, but there are loads of external leaks. Oddly i've had a leak on a T piece for the LPG vapouriser that even after brand new hoses, new metal T and new clips, continued leaking. It also only seems to leak when cold. I suppose if theres a leaky gasket it might seal up when warm... Lots of short journeys seem to consume much more water than one long journey.

Orange insulators and rusting is exactly what I had on #6 on mine - along with slight pressurisation of the cooling system.

Mine leaked a lot like yours is doing - after it cooled down, it would leak from places no matter what I did. If I managed to solve one leak, it would pop up elsewhere. No other real signs of HG failure, no overheating, no obvious sign that it was pressurising - it never blew coolant out when hot etc.

That engine was water-glassed and is 18 months later still holding its coolant.

What is water glass?

Sodium Silicate, it's the active ingredient in Steel Seal although that stuff costs about £50 a bottle. Buying the raw chemical is much cheaper https://www.ebay.co.uk/itm/Sodium-silicate-Water-Glass-500-ml-Free-Post-in-UK/264718636840. Buy the chemical and Google how to use Steel Seal and you're all set.

When it gets very hot, like when it comes into contact with combustion gases, it forms a seal of solid glass. So if, as I suspect, you have a tiny leak between the outside of the liner and the bore in the block that it fits into, it will seal that leak so you won't be burning coolant or pressurising the cooling system. It's about the only stuff I'd consider using as unlike K-Seal, Radweld and all the other magic potions, it remains as a liquid in the cooling system except where it gets into contact with extreme heat so doesn't clog anything else up.