All righty then! Since my MGA is driven a lot it makes a good vehicle for long term testing. Occasionally I can shed a little light on the reality of reliability and cost vs. value, so here is another one of those nifty long term test reports.

I have used lots of different types and brands of spark plugs in my MGA over the years, and they all work pretty much the same for function, performance, fuel economy, etc. So for many years I was using whatever was cheap and conveniently available, which was usually Autolite 64 non-resistor type from the local NAPA store for about dollar each. A high compression race engine might need a little different heat range, but they're still cheap. Being cheap and easy to change in the MGA it's hard to beat the price/value.

I would avoid Champion resistor plugs like the plague. It has been my experience that about 10% of them may be bad right out of the box with far too much resistance, and others may fail in short service for the same reason.

I tried Platinum plugs for a while, purchased at a local discount department store for about $4 each. I don't recall the brand name, but they kept cracking the ceramic insulator off the tip in #1 cylinder, so I gave up on those. They might have been too high in heat range. Excessive spark advance is not an issue in my car with low compression.

Several years ago a club friend gave me a set of Halo spark plugs, model number H-9A. He was selling them, and he wanted me to give them a long test run in my MGA. I suppose he was looking for a rosy review to help sell the things, but I told him up front I don't play favorites so don't expect much. My original expectation was that the things might have a very long life, but otherwise no (noticeable) difference in function vs. any other plugs.

50,000 mile Halo spark plugs

They have been in my car for just over 50,000 miles now. I have never touched them except for occasional inspection during routine service. They have been working fine, running that nice sandy tan color for me, and they will stay in the car for as long as they continue to work.

Subsequent research has shown no upper limit for useful life of the Halo spark plugs, some having run over 100,000 miles, so maybe they will last forever. You can check out the following link for detailed information about Halo spark plugs. Keep in mind it is from the manufacturing company, so as nifty as it sounds it may not be revealing any opposing commentary.

From the WayBackMachine archives: http://www.halo-sparkplugs.com/halohistory.htm
New web site address: http://www.halosparkplugs.com

Addendum, November 2010:
Now at 61,000 miles and still doing well.

Addendum, May 2012:
Now at 68,000 miles on the Halo plugs.
New web site address for Halo: http://lsgbrisk.com

Prior to April 2002, I had driven my MGA 175,000 miles in 15-1/2 years using various brands of spark plugs. While fuel mileage varies considerably under various circumstances, the overall average on an annual basis was about 26-27 mpg. After installing Halo plugs in April 2002, I ran an additional 11,000 miles in 18 months with average fuel mileage was 26-27 mpg (no change). In October 2004 I changed the final drive ratio from 4.3:1 to 3.9:1. Near as I can tell, fuel economy then improved about 1 mpg to 27-28 mpg average (about 4% improvement due to 10% reduction of engine speed while cruising).

In the last 6 months (through April 2012) I have been noticing a hard starting issue. After the car sits for a few days, it may require 7-10 seconds of cranking to start (with full choke), where it previously would start with 3-5 seconds of cranking (with full choke). I'm pretty sure I didn't do anything to change the choke function, so this begs for some investigation. I will first check compression, then verify and/or adjust tune-up settings as required, including points gap, spark timing, valve lash and fuel mixture. Check back later for results.

Addendum, January 17, 2013:
It has been running okay during warm weather, so I left it alone for a while longer. On December 8 2012 I gave the Mallory Dual Points distributor two new sets of points, cleaned up the copper contact rotor, cleaned the copper contact posts in the cap, and checked resistance of all the HT wires. So far so good, but this made no difference in the engine running quality. Two days later on 12/10 I replaced a failed Mallory condenser, which really surprised me, as two prior parts had lasted 100,000 miles plus, and this one failed at 9,000 miles (18 months). Aside from getting it running again, the new condenser also made no difference in running quality of the engine. It is still slow starting.

When the unseasonably warm weather finally turned cold here, on first of the year I parked the car outside and left it out to see how it would do with cold starts. There may be some issue with bad cable connections, because it has a loss of about 3 volts at the starter motor when cranking, so it cranks slow. But the 6 year old battery is good, holds 11+ volts while cranking, and it will keep on cranking for a long time. Had a few successful cold starts and moderate distance trips. After a week of freezing weather it was 20dF at mid day today. Cranking was slow but consistent, and it finally started, but it was running on three cylinders.

The engine had a rare intermittent misfire for some time, but not enough to trace it to any one component. One day it was running okay, and the next day it was running on three cylinders. Finally at 10-1/2 years and 73,000 miles one of the Halo spark plugs failed. While I had it running I opened the bonnet and was about to pull off some spark plug wires when I saw the problem. Number 1 plug had a corona going half way around the ceramic insulator at the top of the steel body. I pulled the connector back a half inch, and it was still doing the same thing. This is obviously spark leakage through the ceramic. One failed spark plug does not make a class action, but that's the end of the test for me. While the Halo plugs lasted 2 or 3 times longer than any prior set of plugs, it probably doesn't justify the high initial purchase price. They certainly didn't make any discernible difference in performance or fuel economy.

I just installed the new Autolite 64 plugs (for which I paid $1.38 each in December 2000), so now it runs on all four. This week end the weather is to turn colder, possibly sub zero (F) Sunday night and temperatures in the low teens on Monday. Monday night club meeting will be a good time to test colder cold start, and see how it runs with new spark plugs. Stay tuned?