Re: 401 operating temperature

[farna@xxxxxxx]

A lot of people with 0.040" overbore 401s report overheating problems. But let's look at some other things:

1) Your engine was designed to run in the 171-242 degree range with a 195 degree thermostat (ref: 1973 TSM, http://www.tocmp.com/manuals/AMC/1973/Service/Part1/Chapter2html/browser.htm; see page 2-5). So you might not be overheating at all.

2) Are you relying on the factory gauge? Specs for the gauge: when needle is on the "C" temp = 130* (73 ohms), start of red line = 185* (28 ohms), end of line = 245* (13 ohms), "H" = 268* (9 ohms). So the center of the red line is ~215*. If you're gogin to the end of the red line it's still considered normal. The only way to check it is to run the engine until it's warm then shut it off, but leave the switch on. Pop the hood then check the gauge. When it reaches a spot you can easily see (like center of line, or one end of the line) pull the temp wire from the sending unit and use an ohm meter to measure the unit. Reading should be within 5% of values given above with temps. If it's original or you don't know how long it's been in there, replace the sending unit.

3) Does your fuel gauge read accurately? If it reads consistently low or high the voltage regulator on the back of the instrument cluster is bad or you have bad connections. The regulator operates both fuel and temp gauges, so a bad regulator or corroded power supply wire to the regulator will affect both gauges. 

4) If you're using an aftermarket gauge do you have the correct sending unit? You need to match the gauge with the sending unit. Most Stewart Warner gauges use the same range as the AMC factory gauge, but check. Does the sending unit fit down into the water stream as far as the factory unit? Not far enough into the water can lead to higher or lower readings depending on location in the engine. Many aftermarket gauges use adapters that may not allow proper placement. 

5) One way to cool the engine further is to use an external oil cooler. If you can, mount it AWAY from the radiator but where it can get plenty air flow. You can get a frame mount transmission cooler that will work just as well as an oil cooler from some hot rod shops. That will work very well, just don't mount close to the exhaust. Temp might go up a bit at idle, but will lower at speed -- which seems to be your problem. Consider a trans oil cooler also. High trans temps not only reduce trans life but can dump heat into the engine also. If you mount away from the radiator (such as under a fender) you might need to install a small electric fan on the cooler. A combo trans/engine oil cooler mounted in the forward part of a fender with a thermostat controlled fan (or a toggle switch so you can turn it off in cold weather) should work well. But you might want to try the traditional in front of radiator mount first. If the trans is part of the problem that will mitigate it by co!
 oling the trans first.


On July 14, 2005 Bill Dettman wrote:
Can anyone tell me about how to keep a 401 running cool. Here's my issue:
I have a '74 Matador X Coupe 401. The engine is a correct 1974 engine. I have had it apart twice. Both times, it wanted to run on the warm side at highway speeds. My Javelin 401 does not have this problem, but it does not have A/C either (yet), and the car is much lighter.
At a constant cruise at 70, with the A/C on, the temp gage will slowly, but surely climb. I never let it overheat, but?I can see that it could overheat if I did not pay attention to it.
I have the following:
0.040" overbore with Sealed Power replacement pistons, RPM Air Gap intake, Phenolic carb spacer, 3-row brand new radiator, factory AMC heavy-duty 7-blade flex fan and NOS brand new shroud. Brand new valves, springs, etc, along with Comp cams XE262H cam kit (nice cam).
Before I had it torn ?down this spring, I tried two thermostats - a 160 and 180. The 180 did better. I have another 160 in it now and will probably go back to the 180. I want to tow on the highway with this car, but I think it's not going to stay cool. Oh, I have one bottle of Water Wetter in the system now also.
Last summer, going to Cordova, it was the same way - if I cruise slower it does better, but I still have to watch it. Ideally I want to tow my Jav on an open car trailer to Cordova. I've towed locally with no problems, but the highway speeds get it heated up. Long idling in hot weather is similar also, but not real bad.
Any tips would be appreciated.

Bill Dettman
'74 Matador X 401, '70 Javelin BBG 401


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