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1,190 Posts
Thermostat:
For the 25 years I drove my 72’ GT, I was always overly concerned with the engine temperature, I thought since these engines had such a bad reputation for cracked cylinder heads living in a warm climate I thought cooler was better, the first GT I bought and the one I’ve had since 87’, the head cracked right away with no indication (it was probably cracked before I purchased it). Rebuilt back then with a good head I still use today. I also purchased a 70’ GT for a parts car a few years later and it’s head was cracked. I used the 160° thermostat for over 25 years. If the temperature gauge got past the 1/3 or 175°F mark I used to start getting nervous. If it crept up to the halfway mark (on those 90+° F days) I’d pamper it and was afraid to push it.
I’ve become more assertive and also discovered that it ran better with the 180° thermostat over the last year or so, the car ran @ 175° mostly just below the 180°.
Recently I started reading more on the subject Bob’s old post mentioned 185° (210° oil temp) was optimum performance temperature. Opel claimed 193° was their findings for best performance according to this post.
Realizing I very infrequently got up to those temperatures I picked up the 189°F/87°C OEM temperature thermostat.
With the cooler winter temperatures right now I felt it was harmless to try. I was surprised how difficult it is to get. 160°, 180°, 195° & 205° are the standard aftermarket temperature.
I realize now our thermostat is common to many other makes. During my search I used this site if you scroll down there’s 1,000’s of different car manufacturers that use the same thermostat. That’s how I eventually tracked down the 87°c T-stat. I noticed Splendid also carries itI was looking for something more local.
Further reading on this subject indicates that the clearances, crank, piston rod, everything on up to the cylinder head were designed for this temperature.
You wouldn’t think it makes that big of a difference but I’m experiencing a definite improvement.
Engine idle is smoother, acceleration throughout more consistent now, better power using less throttle (gas) easy feel on the gas pedal going up steep grades & there to see on my afr gauge, up above the 14’s instead of the upper 12:1’s. Best of all, it’s early but I think I’m paying slightly less at the pump.
Is spark plug heat range related:
I’ve done some further reading on the definition of spark plug heat range to see if it had anything to do with the engine temperature. 🤔 How was it chosen by the manufacture, in our case GM or Opel?
From what I’ve read, spark plug heat range is not related to the engine temperature, a hotter plug transfer’s less heat through the insulator to the cylinder head and more energy/heat to the electrode at the tip of the plug. The colder plug does the opposite. If running rich, use hotter, running lean go colder etc. all related to what comes in the combustion chamber more so than actual engine temperature. Nothing to do with coolant running 160°F temperature at the thermostat vs. 190° F.
I don’t know why but I thought I’d throw the spark plug subject out there for curiosity sake, hoping to learn more.
For the 25 years I drove my 72’ GT, I was always overly concerned with the engine temperature, I thought since these engines had such a bad reputation for cracked cylinder heads living in a warm climate I thought cooler was better, the first GT I bought and the one I’ve had since 87’, the head cracked right away with no indication (it was probably cracked before I purchased it). Rebuilt back then with a good head I still use today. I also purchased a 70’ GT for a parts car a few years later and it’s head was cracked. I used the 160° thermostat for over 25 years. If the temperature gauge got past the 1/3 or 175°F mark I used to start getting nervous. If it crept up to the halfway mark (on those 90+° F days) I’d pamper it and was afraid to push it.
I’ve become more assertive and also discovered that it ran better with the 180° thermostat over the last year or so, the car ran @ 175° mostly just below the 180°.
Recently I started reading more on the subject Bob’s old post mentioned 185° (210° oil temp) was optimum performance temperature. Opel claimed 193° was their findings for best performance according to this post.
Realizing I very infrequently got up to those temperatures I picked up the 189°F/87°C OEM temperature thermostat.
With the cooler winter temperatures right now I felt it was harmless to try. I was surprised how difficult it is to get. 160°, 180°, 195° & 205° are the standard aftermarket temperature.
I realize now our thermostat is common to many other makes. During my search I used this site if you scroll down there’s 1,000’s of different car manufacturers that use the same thermostat. That’s how I eventually tracked down the 87°c T-stat. I noticed Splendid also carries itI was looking for something more local.
Further reading on this subject indicates that the clearances, crank, piston rod, everything on up to the cylinder head were designed for this temperature.
You wouldn’t think it makes that big of a difference but I’m experiencing a definite improvement.
Engine idle is smoother, acceleration throughout more consistent now, better power using less throttle (gas) easy feel on the gas pedal going up steep grades & there to see on my afr gauge, up above the 14’s instead of the upper 12:1’s. Best of all, it’s early but I think I’m paying slightly less at the pump.
Is spark plug heat range related:
I’ve done some further reading on the definition of spark plug heat range to see if it had anything to do with the engine temperature. 🤔 How was it chosen by the manufacture, in our case GM or Opel?
From what I’ve read, spark plug heat range is not related to the engine temperature, a hotter plug transfer’s less heat through the insulator to the cylinder head and more energy/heat to the electrode at the tip of the plug. The colder plug does the opposite. If running rich, use hotter, running lean go colder etc. all related to what comes in the combustion chamber more so than actual engine temperature. Nothing to do with coolant running 160°F temperature at the thermostat vs. 190° F.
I don’t know why but I thought I’d throw the spark plug subject out there for curiosity sake, hoping to learn more.
