Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Changing spark plugs on 3.7 V6 Roadster

With five plus years and 28,000 miles on my 3.7 Roadster I was concerned about the state of spark plugs, particularly corrosion of threads due to water ingress into the deep tunnels they live in. GDI engines seem to suffered from this, often badly. Whilst checking it seemed good policy to change them to the latest spec. Laser Iridium ones offered by NGK.



Research suggested LTR6DI-8 (96588) are the ones and used with success by Mustang owners in the USA. I bought mine from the Green Spark Plug company. The same ones are also recommended for GDI Plus 4 engines. With individual coil packs replacement is easy following disconnection of trigger after sliding out white catch. A single 8mm head bolt secures the coil pack into plug tunnel. Once bolt is removed a twisting and pulling action will release coil pack assembly, although some resist more than others. A smear of silicon grease on waterproof seals will make the job easier next time although with a life span of 80,000 - 100,000 miles I don't expect to be doing this job again. The taper seat plugs are removed and replaced easily with a smear of copper slip on the threads. Thankfully they all came out as new with no signs of corrosion, possibly helped by the 30° angle of heads. A ⅝" or 16mm plug socket with extension does the job and replacements are torqued to 12ftlb. All very easy until you realise the right hand bank plugs are inaccessible until upper inlet manifold is removed!



See image but the manifold is held in place with seven bolts, a row of four towards centre of V and another three further out from centre. I chose to remove manifold with throttle body attached so first unclipped air box cover then released inlet hose clip to throttle body. The large diameter hose can then be eased off. The throttle body connector has a red tab which needs to be pulled out first and this can then be unpluged. Purge valve hose and electrical connector are also easily removed by squeezing tabs on former and pushing release tab on latter.



The outer part of manifold has just one mechanical support (see bracket bottom centre) underneath involving a horizontal 6mm nut and bolt through lug on underside of manifold. These fixings need to be removed. To the left is a hose also associated with the EVAP system and it's hose clip needs to be loosened. The front and back of manifold have those plug in plastic clips with integral cable clip supporting cabling. They both need to be pulled out. The rear one below the K14 label in first image refused to budge for me though and broke off. It was glued back on after re-assembly.

After the afore mentioned seven bolts are then released with the same 8mm socket noting that they are all captive apart from central long one at top of manifold. The loosened EVAP hose to rear needs to be eased off and there is a very short breather hose towards the front underneath which should just pull off manifold stub. It should then be possible to ease off the whole manifold assembly.

The remaining plugs are then easily accessed as before. Replacement of manifold is the reverse of removal although a new gasket, FEL-PRO MS97214 (available from States in a matter of days) is an option given the importance of an air tight seal. No sealant required though. The seven bolts need to be tightened in the sequence shown and torqued to 10NM.



Note it's suggested a vacuum cleaner in plug tunnels may be a good idea for removing possible debris but beware with inlet manifold removed any cylinder with open inlet valves will attempt to suck any protective rag into engine - don't ask how I know

A great job there Richard 👍

Just as well the new plugs last almost forever. A far cry from back in the day when plug suppressor caps were pulled off in seconds to directly expose the plugs.

Well done Richard. Did you have to take the bonnet off to get the manifold out?

No thankfully John. It was a relatively easy job once I'd identified everything that needed to be released.

Great post Richard! Keep them coming!! May I use it in the gomog Roadster section?
I use NGK as well, abandoning the originally recommended Champions 2-3 decades ago! I use their NGK iridiums as well. Despite their pricer they last MUCH longer than other spark plugs.

An important codicil if I may.


In the 1980s, (from memory) some savvy spark plug manufacturers began coating their plug threads with ever more sophisticated solutions to prevent rust, seizing..etc
By the 1990s all manufacturers were doing so. Adding anything became unnecessary, even prejudicial as it can can combine with the manufacturers precaution and definitely changes the important torque readings, by 20%+. It also increases the possibility of the plugs seizing. This is why your old spark plugs came out unseized and pristine.

The use of any other coating is strongly advised against. https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs More by NGK than even other manufacturers. But old bad habits die hard. The debate, rather lopsided now, continues. Google "should I use copperslip on spark plugs"

If you choose to remedy, change the plugs and carefully clean the threads in the head.

Be well.

gmg.

I had heard the same Lorne although plugs I've seen pulled out of GDI Plus 4's, particularly number one can look quite corroded. I use copper slip more for ease of removal though. Feel free to use the article.



An addendum though. The image above was taken before I cleaned the normally hidden right hand bank. The short breather tube fitting into base of inlet manifold can clearly nearly be seen below right hand coil pack but also a patch of oil residue surrounding same. I removed the grey plastic non-return ball valve (quarter turn out of valve cover) and cleaned it out but added a hose clip to upper part where the hose was a not particularly tight fit onto the manifold stub.

Great info, thanks Richard

Although you mention no corrosion, were the OE plugs still in good condition at the business end, any erosion of the gap ?

They all looked similar Jon but with what appeared to be stubby centre electrodes with gaps measuring close to 1.4mm say 35 thou. Motorcraft platinum plugs as expected but with an NGK code stamped on the hex suggesting they are made by them for Ford. The -13 suffix of this code suggests a 1.3mm pre-set, so they have worn a bit.

I was changing the air filter yesterday so decided to have a look at the NS bank of spark plugs. I.e. not needing to remove the manifold.

Came out relatively easily with no signs of corrosion or seizure and in excellent condition with no tip erosion at about 53 thou gap and a lovely light / mid brown colouring.

This is after 30,000 miles so just put them back in

Standard plugs....Motorcraft AGSF32N

PS..... 3.0L engine

Thank you RichardV6. You are kind to your brethren. However, I will remove the bit about copperslip and add the NGK warnings about it. Is that ok? The rest of you post will help the Roadster community mightily.
Lorne