Best spark plugs for hard-to-start 230SL?

[dsayars]

Nov 13 Update: Thanks to everybody for your helpful responses. I'm happy to say I'm seeing some improvement since switching to the hotter plugs. This morning, in 40 degrees, it started quickly then quit, but started quickly and stayed started on the second attermpt.  As I told James, this may be combination of  the plug swap and also the fact that I'm actually starting the car every day instead of every now and then. (As with all cars, the worse they get the less you drive them, and the less you drive them, the worse they get

My car has had ongoing start problems that are always correctable by removing the plugs, cleaning them, and putting them back in, a simple but tedious solution. The plugs are Bosch W7DC as per spec. dseretakis mentioned in this forum that he finally got his non-starting 280SL going with NGK BP5ES plugs, which are not equivalent. Can anyone tell more about this particular swap? Is it generally considered an improvement? Are the NGK BP5ES's non-resistor, and if not, is this a problem? My current plugs are non-resistor and there's a capacitor mounted on the distributor for RF interference.

Thanks in advance to anyone who can tell me more about this.

-Dave

[J. Huber]

I have used the BP5ES plugs for many years with great results. They are non-resistor and I believe would be the equal to WR9DCs. So a little "hotter" than the BP6s or WR7s...

You may also want to confirm your Cold Start Valve and Thermo-Time Switch are working correctly. That was what finally cured my starting troubles.

[dsayars]

Thanks, James. You say they're non-resistor. The ones I looked at appeared to be resistor, but modern plugs confuse me a little. On the old ones, the resistors screwed off, now they mostly don't from what I've seen. These BP5ES plugs had the old sllver (vs. black )resistors but they didn't seem to screw off. Perhaps they do with a little more effort?

I've been through the CSV and WRD pretty thoroughly in the past. The CSV wasn't seating and leaked, I fixed that, the WRD was stuck in the warm postion from coolant seaping in and corroding things. Both were in good working order based on a recent check, and the fact that it fast idles when it does start tends to eliminate the WRD. It's also true that you can't check these two devices too often, particularly when the WRD has a coolant leak

[lurtch]

Hi Dave

I struggled with  spark plug choice a lot when I first brought my 230SL back to life after a 5 year hibernation. I finally got tired of messing with the three different sets of plugs. I   wised up and installed a PERTRONICS Capacitive Discharge ignition kit ( optical trigger ) and their companion High Energy coil. This setup will throw a half-inch long spark.  My plug troubles immediately disappeared - - - .

Larry in CA

[jacovdw]

...On the old ones, the resistors screwed off, now they mostly don't from what I've seen. These BP5ES plugs had the old sllver (vs. black )resistors but they didn't seem to screw off. Perhaps they do with a little more effort?

Hello Dave,

James is right, NGK BP5ES is definately a non-resistor plug. I think you are referring to the aluminium screw thingy at the top of the spark plug. That is not a resistor, but a removable cap the allows you to use the plug with different plug wires. They can be removed with a bit of effort.

Generally speaking, the heat ranges differ between Bosch and NGK spark plugs. The higher the numerical value of a Bosch plug, the hotter it is. With NGK it is the other way around (ie. the lower the number, the hotter it is).

Resistor plugs generally have a R in the naming and that is applicable to all manufacturers, ie. NGK BPR5ES is a resistor plug.

If you have a standard ignition, your basic plug gap should be 0.7mm. In short, resistor plugs are a big no-no for pagodas...

Hope this helps.

[Naj ✝︎]

Dave,

You can also significantly improve starting by bypassing the ballast resistor.

Have a look at the Bosch Leaflet in the wiki:

http://www.sl113.org/wiki/Electrical/IgnitionCoil

naj

[jameshoward]

Dave,

Whilst a symptom of the problem you have appears to be that the plugs foul and a good clean sorts things out, the cause may not sit with the plugs or wires. It may be that the car is running improperly (timing, mixture) thus fouling the plugs. The plugs shouldn't foul that much if the engine is correctly set up. You may wish to consider giving the linkage tour a visit, and then ensuring that the dwell, timing, etc is correct, see what your compression is, valve settings, etc. You might find you're trying to solve the wrong problem by looking at the plugs in isolation. But then again....

Jacovdw pointed out the 'R' for NGK resistor plugs, the same is true for Bosch, eg WR9PD.

JH

[Benz Dr.]

The recomended plug is W7DC which is too cold. The W9DC is just about right but is no longer available or at least I can't find them anymore.
The NGK plug would be my next option.

[66andBlue]

...  or at least I can't find them anymore.

Dan, don't tell me you ignored this!  
http://www.sl113.org/forums/index.php?topic=11230.0

[J. Huber]

I've been through the CSV and WRD pretty thoroughly in the past. The CSV wasn't seating and leaked, I fixed that, the WRD was stuck in the warm postion from coolant seaping in and corroding things. Both were in good working order based on a recent check, and the fact that it fast idles when it does start tends to eliminate the WRD. It's also true that you can't check these two devices too often, particularly when the WRD has a coolant leak

In addition to the WRD and CSV, it may be worth a look at the TTS (thermo-time switch) on the block above the IP pump. Once I discovered mine was kaput -- I cured my hard cold start issues (6 years later, not one hard start...many many easy ones) (unless you count a dead battery... had one of those)...

[dsayars]

In addition to the WRD and CSV, it may be worth a look at the TTS (thermo-time switch) on the block above the IP pump. Once I discovered mine was kaput -- I cured my hard cold start issues (6 years later, not one hard start...many many easy ones) (unless you count a dead battery... had one of those)...

I think what you're describing is the sending unit to the thermo-time switch, which is mounted on the head and activates the TTS to  prolong the operation of the cold start valve and cold start magnet when the engine's is cold?  I have checked this circuit in the past and seem to remember that it was doing something at least (I got more than the minimum one-second spray from the CSV) but it could bear looking at again. Question: on your car, was the fault in the switch, or in the sending unit? I suspect the latter since that's what you describe.

[J. Huber]

I think what you're describing is the sending unit to the thermo-time switch, which is mounted on the head and activates the TTS to  prolong the operation of the cold start valve and cold start magnet when the engine's is cold?  I have checked this circuit in the past and seem to remember that it was doing something at least (I got more than the minimum one-second spray from the CSV) but it could bear looking at again. Question: on your car, was the fault in the switch, or in the sending unit? I suspect the latter since that's what you describe.

Well, I am not quite sure about the sending unit part versus TTS -- the thermo-time switch I replaced was the one on the block (about 100 bucks from Bud's). This thread in the wiki describes the tests and function very well.

http://www.sl113.org/wiki/Engine/ThermoTimeSwitch

[dsayars]

Well, I am not quite sure about the sending unit part versus TTS -- the thermo-time switch I replaced was the one on the block (about 100 bucks from Bud's). This thread in the wiki describes the tests and function very well.

http://www.sl113.org/wiki/Engine/ThermoTimeSwitch

You're right  & I'm wrong. The "sending unit" is the TTS, the other part is the relay. From the circuit diagram in the shop manual, the TTS appears to draw more current though the relay coil the lower the engine temp is, but is prevented from flooding the engine by the fact that it heats itself up in the process. If that's true, the time you have to allow between start attempts is the time it takes for it to cool down from the self-heating, 10-20 seconds.
Anyway, I'm happy to say that the car started quickly on my first attempt this morning in 40 degress, then quit, but started quickly  and stayed started on the second attempt. If this keeps up, chances are the TTS is good. Improvement is probably thanks to combination of putting in the hotter plugs and actually starting it every day, not just from time to time. (The less you start them, the less they start.)

[dsayars]

Dan, don't tell me you ignored this!  
http://www.sl113.org/forums/index.php?topic=11230.0

Sorry, I ignored you because you seemed to be taliking to someone named Dan, not Dave.
I bought some NGK plugs and they seem to be helping. With the Bosches as rare as they are (?), I'm sure you'll have no trouble finding a buyer.

[66andBlue]

Yes Dave, you are correct.  That was a reply to Dan Caron's message as you can see from the line above my original quote.
Glad to learn that the starting problems are disappearing.

[hands_aus]

To test the TTS and relay I use a small 12V led lamp as a test light connected between the center terminal of the CSV and earth.

If it lights and then goes off, the TTS and relay are both working properly.
If it doesn't light then you start checking the relay first then the TTS.

Similarly I have test lamp between the center terminal and earth of the CSS on the back of the injection pump.

The relay can be cleaned and adjusted.
Check the Technical Manual.

[glenn]

It ain't the plugs!!!  Valves adjusted, timing, points, gap, dwell, rich/lean, etc, etc. .. Is it idling at 750-800 rpm 50 rpm rich?   Rack relay energized, CSV open for correct time(based on coolant temp), air slide valve working right, etc. .. It's hard not to start, if everything is in sync. ..