Well, let me know when you find out, my 68 also is running very hot, doesn't help that the temps have been 97 and 98 here in Thousand Oaks, put in a 160 thermostat, changed to a 6 blade flex fan, which helped, now I'm doing a long radiator and block flush, my next attempt will be a three core radiator. Is this something that has just started, or has it been that way? jim
Hard to say if this is something that just started or not. The reading on the gauge was always close to "C". But, I noticed the previous owner wrapped tefon tape around the temp sending unit and that was giving me a false reading. I replaced the temp sending unit with a new one (NAPA) and now it reads 3/4 hot all the time.
BTW, the previous recently had the engine rebuilt. I wonder if some junk got into the radiator? Perhaps a gano filter would be a good idea?
Like...all the time? It should be cool at first start up. The only way to tell whats really going on is a temp bulb/thermocouple or an aftermarket gauge. I had a similar problem, it came down to either the indication or a true heating problem. I bought a multimeter from Sears that also had a temperature attachment, I ran the engine until it got hot, shut it off for about 5-10 min, until I could SAFELY remove the cap and I took a reading. It helped with my problem.
so what's temperature of the thermostat you bought? I have a 180 degree thermostat in my mine and it sits about the middle. I am gonna buy a aftermarket temp gauge to get a better reading. Really the only time my car gets a little hot if I am sitting in traffic for a bout a hour so. Yeah I believe our cars came originally with a 160 just for your info
I have a '69 that drove me crazy every time it got near 90*. It never really overheated ,but got darn close. Water Wetter will help. I cured mine for good with a four core. Be sure to check the usual cuprits like timing and so forth. The original radiators had marginal capacity to begin with and after a few years they fill up with crap. No one expected them to last beyond 5 or 6 years. They originally came with a 180* thermostat. Good luck.
I'm having the same problem (have been all summer). I recently flushed the system with Prestone's Super Flush. I then filled the system with water and added Watter Wetter (no coolant). It's running much cooler but I'm still not satisfied.
I think my biggest problem is I'm running no fan shroud, and the current fan sits 2-3 inches off the radiator. I just ordered up a SPAL fan from streetortrack.com
OK, my 2 cents worth: the thermostat has no effect on whether your car will run hot or not because once the stat is open, whether it's a 160 or a 190, the cooling system will reach an equilibrium.It simply determines at which temperature the coolant is allowed to leave the radiator, thus determining warm up time.
One easy thing to do if you question your guage is after you park the car from a drive where everything got up to operating temp, open the hood and simply listen for sounds indicating it REALLY is hot, such as a lot of popping noises as well as coolant running out the overflow hose (if there isn't an overflow bottle).If everything appears to be normal, then it's simply the old style gage innacuracy.
Another neat device is one of those LED readout hand held things that you point at the radiator and it will readout the correct temp.I think you can get one at NAPA.
To determine number of cores in your radiator, just remove the cap when it is cool and look inside with a flashlight. You will see slots running left to right across the radiator. Now look from front to rear and there will be either 2, 3, or 4 rows (or cores) of these slots.
I ran into the same problem you did. I was told by my radiator guy that these cars were always were marginal. SO I ended up replacing my radiator with a new 3 row. A lot of things will make it run hotter: incorrect timing, too much paint on the engine or radiator cooling fins, corrosion in the engine/radiator, etc.
Here's a simple test for you. Starting from a cold condition, run the car with the heat on and the blower on full. If you see an improvement replace the radiator.