Some recent very good threads on here have had me thinking more on bellows thermostats and, the engine cooling system in general. I’ve just finished a full blown rebuild of my engine but have yet to start it up (as other mechanical systems need to be addressed too). Anyway, while researching here (three hours reading of old threads!) the different fan belt sizes used, and having bought, then subsequently returned, three different belt sizes, it forced me to more critically look at the engine drive pulley. It should be obvious from the pictures attached which is the original. It came off of my early F-series engine (late '53 into '54). It wasn’t lost on me that though most belts sat in to the pulley okay, all of them, including the last one used, did not sit flush with the outer edge of the pulley. I think this is important though I almost missed it. These pulleys have a diameter of 5". By using modern belts (in my case a Gates B36 or a 5L380 or 5L390, they sit about a 1/4" too deep meaning that pulley now has an effective diameter of 4.5". According to my calculations, that translates to both water pump and generator turning approximately 200 rpm slower than what they normally should. Maybe not an important issue at speed, but I would think that when the car is idling in traffic it would. Generator would require slightly more rpm to cut in and the water pump wouldn’t be circulating coolant fast enough.
The takeaway here is that if you have a car whose fan belt sits noticeably less than flush with the engine pulley outer diameter in particular, then consider either trying to find an old size that will more accurately fit it, or, replace it as I did. It’s my understanding that these later pulleys have a belt profile that’s long obsolete. I know that one of the usual vendors sent me something that was so large and stiff as a replacement that my initial thought was that this is something more suitable for a tractor than my car. And if it were to fail, there’s no way I could get a same size replacement on.
New pulleys are made starting at approximately $145 plus tax and shipping. But I don’t know the belt specs they’re made with. So, for the $12 purchase of a 5" diameter, 1" thick round of 6061 from McMaster-Carr, I turned my own using the old pulley of course as the pattern. Very happy with the results though set-up made for some head scratching. The four bolt holes I did on my mill with the rest being done on a near 100 year-old Seneca Falls “Star” lathe using a faceplate and three and four jaw chucks. Fortunately, I can still get 0.001" accuracy out of it. The upshot is that I can now use commonly sourced 5L— and B-- type belts while everything is spinning at the correct rpm. And if the belt breaks on the road, obscenities and gymnastics while fitting a replacement are lessened. I hope.
You’re only going to move as much water as the thermostat will allow, typically the pinch-point in the system. It’s there to act as a flow restrictor. I’ve got a pretty good feeling that as designed the system is fairly well balanced between air flow, coolant flow and the ability for the engine and radiator to release heat to a nearby conductor.
Installing a radiator with a larger surface area is about the most important first step to take, for without shedding heat more quickly, nothing else matters. No matter how fast you move the coolant, it’s got to give up the heat to air.
Another consideration to rotating the water pump faster is cavitation. Run any propeller or impeller too fast and it will cavitate when the water will not move fast enough to get out of the way.
Hot water in the system is quite close to boiling. Reducing pressure even slightly brings it to a boil, however briefly. Boiling water impedes its flow.
Pressure systems help to prevent this. I have no idea what the tipping point might be.
…which is one reason why I run Propylene Glycol waterless coolant in all my cars, and have done for the last twenty years. I can run the cooling systems at zero pressure.
as author of lenhty thermostat-cooolin posts…which you can find…I will be brief…the XK should have a 4psi radiator cap. Not 7, certainly not 15. Thus pressure will always be low in the system…as the cap will release above 4psi. Air thru the radiator is the key…if all else is in operation as designed, in a clean system. Transfer of heat from coolant to air can be aided with "water wetter " type products…but only a little. Denny Hamlin just lost the NASCAR championship because too large a piece of tape was placed across the air intake to radiator…an attempt for more speed.but the car overheated immediately.
Nick
Well, if it works for you, then that’s great Rob. The old belt on mine was riding on the bottom of the engine pulley v-channel – and not the sides like it should. Plus, the v-channel had deep grooves and had lost some of its profile. That was enough for me to turn a new replacement on the lathe.
and just a note on belts.not only can there be pulley differences, on either or both of fan or generator, .I have seen at least two belt adjuster link plates…the one attached to the generator…that alter the belt length.
