The temperature gauge in my '66 Toronado creeps upward quite a bit on hot days with the A/C on, particularly if the vehicle is not moving. The gauge has no numbers and this has always been a concern (needle moves to about 5/8 of range), so I installed at 160F thermostat to buy me a bit more time.

Yesterday was quite hot and I had the engine as hot as it has ever been. I pulled out an infrared gun and the hottest temperatures I could read at the top of the engine were in the 205F range, which seem quite reasonable. My only concern is that oil pressure drops to about 10PSI in drive, when normally it is 15-20 PSI.

It also seems to me that the cooling system becomes more efficient as coolant temperatures increase.

So how hot can one run a 455? Thanks.

 

None of what you describe sounds abnormal; it is summer, after all. A lower temperature thermostat is just going to stay open all the time. It's probably not going to do much different, other than open earlier.
As far as the oil goes, you should be running a quality 15w-40 diesel oil to help the flat tappet camshaft live.

 

Unless the engine has been changed, a '66 Toronado has a 425. Nothing you have described is unusual.

 

Keep in mind that under 16 psi, your coolant doesn't boil until at least 250 F. And modern diesel oils don't have the ZDDP levels that they used to. I use high ZDDP oil in 10W-30 or 10W-40. Amsoil, Driven, VR1, etc are all equivalent.

 

Thank you guys.

Engine is not original.

Oil is 10W30 VR1.

I'll carry the temp gun so I can get more data points.

 

I'm aware. The deal is that a lot of guys won't pony up the cash for proper oil, especially on a stock engine. I recommend 15w-40 diesel for its economy.

 

You might consider hooking up a calibrated gauge temporarily, just so you can get some idea of what temperatures the needle positions on your factory gauge actually represent.

 

First things first, keep in mind an IR temp gun is only as accurate as you are at estimating the emissivity of what you’re trying to measure. Best bet is measuring the temperature of the radiator hoses and setting the emissivity of your gun to .9-.95. If your thermostat housing is painted, you can also measure that. Also, you want the water temp - not the block, not the heads, not the valve covers.

Second, where does the temp gauge read when it’s cold out compared to hot with AC on? My repop rally pack temp gauge sits at about 1/4 when fully warm at 180 F. Middle of the gauge is way too hot on mine (I spun a bearing in my small block pushing it).

Third: check your fan clutch. Mine was rock solid, except with AC on. Then it would creep up, especially sitting still. Fan clutch wasn’t worn enough to have issues normally, but couldn’t keep up with AC.

 

All seems normal to me. Stick with your oil. You don't need heavier weight oil. Olds specs are 1lb per 100 RPM. So only if your idle is above 1000 should you be concerned. As long as at higher RPM it's at least 30 you are good. Don't worry about the temperature either. It's only a problem if it goes into the red zone. As Joe said 250 is the max.