Hotter spark plugs to avoid oil fouling

Which plugs would you use to step up the heat range one step for to burn off the oil and keep the plug cleaner longer?

1987, Renix, 4.0 L, 288,000 miles. I have two cylinders leaking some oil from worn valve stem guides. Looking for a short term fix till I can pull the head....I want to go one step at a time hotter on the plug till I find one that works. Tired of cleaning the plugs every tank of gas.

Tried new valve stem seals, got about 5000 miles the last 3 years ( I was sick in bed most of that time) before the bad valve stem guides got to them again.

I was using Bosch Copper core, platinum coated tip plugs that worked great till the new valve stem seals gave up. Switched to the NGK FR5 7373 plugs this week on the cyls that are getting oil fouled. Want to try one setting hotter next. How do we find interchangeable plugs (thread size, length, resistor core, etc that fit with a heat range comparison chart?

What is the 4.0 stock compression ratio?

Just found this:

• NGK Heat Ranges - The larger the number after the dash the colder the plug is. Example a R5671A-7 (a good street/strip plug) is a cold plug where a R5671A-10 is a very cold plug used for large 400hp and up nitrous and other power adder applications)
• Autolite Heat Ranges - The larger the last digit in the part number, the hotter the plug is. Example a AR3935 (good street/strip plug) is hotter than a AR3932 plug which is very cold used for lots of nitrous.
• Champion Heat Ranges - Typically Champion numbers in the same series the larger the number the hotter the plug.

Here:


http://www.dragstuff.com/techarticles/spark-plug-cross-reference.html

This FR4 NGK plug, NGK 5155 FR4 V-Power Plug, has the same exact specs as the FR5 I installed 2 days ago, but has a hotter hear range of 4 instead of 5.

I may try one of these next

https://www.ngk.com/product.aspx?zpid=9755

this week in cyl 1, next to the FR5 in cyl 2. Compare the two plugs after 200 miles if there is no miss firing from the FR4.

Still looking for input, feedback, ideas here.

I use ZFR5Ns in all my 4.0s.

Do they make one in a 4?

What's your oil pressure like? Maybe run 15w40 for a bit?

Have you ever considered going the route of putting air on the plug hole to hold the valves closed, while changing the valve seals in-situ? I made a nifty leverage tool held by a rocker stud and nut with a window for pulling the keepers. Fits all kinds of heads, too.

If you are going to do a valve job, have them ream and bronze sleeve the guides. Never knurl the valve guides. It lasts for about 10k miles then is worse than ever.

Another option is to go with valves with slightly larger stems. There is a company that chrome plates the stems to make them a bit larger and they are hard as hell and will last forever.

I didn't know anyone reamed guides anymore for the above reason.

cruiser54 said:

I use ZFR5Ns in all my 4.0s.

Do they make one in a 4?

Click to expand...

NGK does not show that as being usable on 4.0s.

Overland said:

What's your oil pressure like? Maybe run 15w40 for a bit?

Have you ever considered going the route of putting air on the plug hole to hold the valves closed, while changing the valve seals in-situ? I made a nifty leverage tool held by a rocker stud and nut with a window for pulling the keepers. Fits all kinds of heads, too.

Click to expand...

22/32 psi hot, 32/50 psi cold on oil pressure, using 20W50 in the heat belt up to 105 F ambient. I already replaced the valve seals about 2000 miles ago. AT that time it was obvious the valve guides were oval-ed out. I used rope shoved in through the spark plug hole the hold the valve up.

old_man said:

If you are going to do a valve job, have them ream and bronze sleeve the guides. Never knurl the valve guides. It lasts for about 10k miles then is worse than ever.

Another option is to go with valves with slightly larger stems. There is a company that chrome plates the stems to make them a bit larger and they are hard as hell and will last forever.

Click to expand...

Thanks. I use to sell and service those hard chrome plating units. Krome-King was the brand, back in the 1970s. Awesome stuff. Oil field industry here is a huge user and they use electroless nickel as well. Great for building up the diameter on worn steel hydraulic cylinder rods and making them nearly wear proof.

I had mine bored and bronze sleeved when I built my stroker. At the time I couldn't find oversized valve stems. You used to be able to get them for about any motor, but they are in short supply any more. A year or so later I ran across a company who offered them. I can't remember the name but they were an American company somewhere in the Midwest.

Overland said:

I didn't know anyone reamed guides anymore for the above reason.

Click to expand...

My machine shop does it all the time and were not that expensive. I think they added around $8 a valve since they were doing a valve job anyway.