Radiator Cap



I got a 200 66 Mustang. Right now, I'm using a 6-8 psi radiator cap, I'm planning to use a 16 psi soon. I got 4 rows done by my machinist.

BTW, is it normal that when you start the car the needle in the TEMP gauge is almost "C". After an hour of driving or so, the needle moves about a quarter but it never reach the halfway mark. Is this normal?

It almost seems as if your car may be "over cooling" I know there are a lot of guys that really like the 4 row rads, but I think that for a stocker it is a bit much. A 3 row would be just fine. I do feel that the stock 2 row can be inadequet in many circumstances, or parts of the country that see many temperature extremes. Make sure that the Temp Sending unit is operating correctly. If it is, the maybe you need to put a higher temp thermostat in. This will delay the opening, your car will heat up faster. But as I stated earlier, make sure Temp Sending Unit is working properly before you proceed.
I am running a 13lb cap with an overflow tank, stock 2 row rad, and a 180 deg thermostat. Runs in the middle al the time.

I have a 4 row radiator. Either my thermostat won't close (robertshaw, supposedly good), My temp guage is wrong, or my car is overcooling. In the winter it will barely go over 160 even though I have a 180 degree thermostat. This after being running/driven for a long time.

hmm but the 180 means that thats when its fully open right? If my cooling system is good enough, and unfortunately it is, then it still might keep it at 160-170 eh? The block and head is really quite clean, new 4 row rad, good hoses, new thermostat, new water pump & belt, think it just might be running that cool?
Ideally you want the car to run between 185-195 for best economy.

I was running a 180 stat and 3 row radiator and was getting consistent 165 temps. This was because the thermostat was staying open too long and the fluid from the radiator was too cool.

I need the 180 stat in the summer when it gets in the 90's here. But in the winter I run a 195 stat which on cold days usually runs round 185.... in traffic it can hit 196 or so....

I also pulled the temp gauge when I did the dash and installed a good reliable gauge that reads in degrees, life has been easier since then.

Anyway with the larger radiator I noticed the temps drop to match the therm they are serving or run a tad under. With the 4 row radiator I would go out and get at least the 195 stat for the winter months... Experiment it only take a few moments to change the stat.... also hook up a gauge or therm. to you radiator and see what temp that gauge actually opens at. A lot of them are incorrect. I went through a couple last time finding ones that openned when they should.
I think you have a valid case of over cooling. Just changing the thermostat with the same temp, but new seems like a good place to start. Also make sure Temp Sending Unit is functioning properly.

What you are describing sounds like the t-stat is opening gradually or is stuck in an open position, which doesn’t allow the block to reach temp.

To check the operation of the t-stat, remove and place in cool water on the stove. The t-stat should stay closed, until the water temp reaches the designed value, say 180. At that point it should open almost all at once. If it opens gradually or not far enough, replace. I use a simple candy thermometer capable of reaching well into the mid to upper 200 degree range.

Good luck and be sure to check the new one the same way, Ric.
Overcooling should never be a problem if your system is operating properly. If the t-stat is closing, it wouldn't matter if your radiator was the size of a swimming pool. The engine would reach operating temp and then stay there. 2-4-6-12 row......