Autolite 764 vs. 103 and GT40 operating temp

[h2ohangtime]

I know this has been beat to death as far as the right plugs to get for a GT40 (Autolite 764 is the WIDELY accepted answer), but I'm trying to take it a step further:

Right now, I have the Motorcraft AWSF22C (~Autolite 103) plugs per my manual and my engine only heats up to about 145* and runs a little rich. Since these plugs (as far as I can tell) operate at one heat range colder than the 764's, would it make sense that by installing the 764's, I would expect to see my engine bump up to the normal temp of 160*?

I'm just trying to figure out the rationale that the authorities (WhiteLake, PCM, CorrectCraft) are using for the change in heat range from what's listed in the CC Manual for my SAN.

[DanielC]

My understanding of the heat range on a spark plug is this.
A colder plug transfers heat quicker from the center electrode to the cylinder head, therefore it is a colder plug.
The difference in the amount of heat actually transferred to the head, and then to the cooling water from a different heat range of plug, in comparison to the amount of heat transferred directly to the head, and cylinder is so small, I doubt you could change the cooling water temp, until you went so far out of range, that the engine misfires, and generates no heat, or preignites and make too much heat, right before it destroys itself.

If you are trying to change the engine temperature, change the thermostat.
I would not trust the gauge on the dashboard and the absolute last word on what your engine temp actually is.

[NigelC]

I agree with Daniel.

Change the thermostat.

[2gofaster]

A colder plug will typically allow more ignition advance in a given situation, before detonation or pre-ignition is induced. Thus, it will increase the detonation threshold. Plug heat range will not affect engine coolant temp when used by themselves, unless you misfire. I would run the hottest plug you can without rattling/detonation/pre-ignition.

[h2ohangtime]

Well, I guess I'm back to square one, then. I changed the thermostat (another 160*) a couple weeks ago to no avail. It probably needs new plugs anyway, so I'll put the 764's in.

I guess the next thing to check is the ECT sender and the gauge...

[DanielC]

If you download the GT-40 service manual from this site, i believe it has a chart on the temperature and resistance curve.