OK, so here is another dumb-dumb question. I have installed an overflow tank in the Dart, (finally), by cutting a 2" hole in the inner fender and mounting the bottle under the fender with just the top sticking through. But I don;t see how this radiator cap can pass fluid back and forth in and out of the bottle. It does not have the little disk in the center of the plunger that most caps have. I'm thinking I am lucky this thing has not burst the cooling system open yet. This cap has been on here since I bought the car, and I never even questioned if it was good, or bad. With all the high tech things I have done to upgrade it, I never gave this little simple piece of technology a thought.

When done I will have two caps. One will be on the cross flow alluminum radiator, and the other will be on a filler cap insert installed in the upper radiator hose. It seems as if the overflow hose should go to only one of these, and that the cap should be different. The one with the hose should be able to vent, and the other should not.

How does the "modern" (anything after 1969) radiator cap work? And, which of these filler caps should get the vented cap, and which one should be sealed off tight? I purchased a Morroso cap along with the upper filler section that says "13-16lbs, for racing use only". It has the vent disk in the center of the underside. Does this get pulled down when the coolant contracts? And why would it say "for racing only"? Is that an EPA regulation to keep it from having to pass some government test?
Please feel free to give us a lecture on cooling system theory. I want to know as many usefull things as you have time to type here.

On my brother's 2.2 turbo engine, we ended up drilling a small hole in the thermostat to get the block to fill after draining it. It seems like a good idea to me for the slant. Any drawback to this?
Sam

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I just removed the old thermostat, and it has a small hole in it from the factory. The new one does not. But, the openings in both thermostats seem rather small. It is not as big as the one in my brother's 2.2 L. It seems like this might be a major restriction in the system. Is there another part number that is bigger that would still fit the slant housing? ? Is there any wisdom in this? This engine generates a great deal more heat than it did stock. The new extended plug design worked much better than the oem design, is there maybe a similar improvement to be had with the thermostat style?

Sam

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about 1/2 way down:

http://auto.howstuffworks.com/cooling-s ... /printable


the thermostat probably has a small notch in it where the center section mates to the outer instead of a hole.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Yikes. Wrong cap. Get it offa there.
H'mm. How come?
I agree.
See this post
I'm still a little confuzzed as to why you're putting two caps in the system, but if there are to be two caps in the system, I would probably put the cap that allows flow (don't say "vented", for that word means something specific in this context) at the highest point in the system.
I don't like this sloppy "13-16 pound" stuff. Which is it? 13? 14? 15? 16? Both the factory and the real aftermarket (companies in the business of making radiator caps, which doesn't include Moroso) make different caps with all these different ratings. It can be done. It should be done. It is done.
There are no regulations on radiator caps. I'm not familiar with whatever Moroso are selling as a radiator cap, but it would take some doing to convince me there's anything such as a legitimate "Race only" radiator cap.
The purpose of the thermostat flange hole (or notch) is to permit air to move from behind the thermostat as the block fills, which happens from the bottom up, not so much from the top down. The hole or notch needn't be very big at all, but it does need to be placed in the 12:00 position when the thermostat's installed. If this hole is too big, it emulates a thermostat that is stuck partially open, and engine warmup time is slowed with concommitant losses in economy and driveability and increase in engine wear and oil contamination.

Go see if you can find a Stant SuperStat. P/N 45356 (160°), 45358 (180°), 45359 (195°). These are the best thermostats currently made. Don't recall if there's a hole in the flange, think not, believe these have a small V-notch in the valve plate or other more subtle mechanism serving the same purpose.

Stant used to make balanced-sleeve thermostats in addition to the reverse-poppet type you're used to seeing. Robertshaw kept making them after Stant mostly stopped (you can still get a Stant 14429 balanced-sleeve thermostat; it's a 190° item and they don't offer any other temperatures in this design any longer). Robertshaw kept on making these thermostats, and then Cooper-Standard bought Robertshaw's thermostat operations (this is neither the Cooper nor the Standard that we normally think about when hearing those names). The Robertshaw line still contains the 330-180 and 330-195 balanced-sleeve thermostats, no longer the 330-160, though if you're curious what one looks like, have been convinced that 160° is a good idea (I haven't), and want to try playing with it, you can pick up a Stant 330-160 very cheaply here. The balanced-sleeve thermostats have a potentially larger opening, but However, be advised that I've never been able to make one of these fit into the thermostat hole in the slant-6 head, and even if you grind the thermostat hole slightly to make it fit, I am pretty sure the sleeve will hit the head casting when it tries to open. Dead end trail there. Don't worry about the thermostat acting as a restriction. That's part of its job.

Stant Superstat info from the manufacturer is here .
Good discussion of cooling system components and thermostat types here.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'm gonna guess that the top of the radiator will be below the head. That would be the only reason I know for having 2 caps. Yes, the hose should go to the higher point.

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Official Cookie and Mater Tormentor.

Maybe this is not essential, but the second cap is because the radiator, being a cross flow, has the cap down low on the passenger side tank, and the upper radiator hose is long, having to come from the driver's side tank of the cross flow radiator, had to be extended high to get over the fuel rail, and the Sanden AC compressor. It is up there within 1/2" of the underside of the hood. This leaves a large expanse of hose that I can not get to fill by putting coolant into the radiator cap. I am sure there are air gaps in there. So, I put the upper radiator cap into the upper hose so I can get it completely full. Maybe the overflow tank makes this unnecessary. I was planning this upper filler spot before I engineered the over flow tank into the system. My '95 Corvette had a sperate filler tank that was above the engine, a cap on the radiator, and an overflow tank way down low.I am kind of mimicking that.

Thanks for the tip on the thermostat. I will see if I can find the stant 180 you referenced. The hole in the old thermostat was about .040 in diameter. It would be simple to drill something this size in the new one.

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With two caps I would try to use a sealed cap in the lower position, and the normal cap at the high point where the overflow will connect. I think the sealed type of cap may be an old ford type of cap, some of them had expansion tanks, not overflow tanks and had two caps.

In the interest of better cooling I would run a 16 psi cap. It will help minimize the forming of small bubbles in the system and give you a higher boiling point.

I looked at using one of the balanced style thermostats in the slant too. It didn't look promising. The stant superstats Dan mentioned are what I have been using lately when the balanced type is not available. They have a notch in the poppet. If you want more I would block the poppet open and file the notch a little bigger. The notch is self cleaning, I have seen drilled holes plugged several times. Anything that gets in the coolant ends up in the hole.

I installed the 180 thermostat, filled the system, started the engine, and let it idle for 20 minutes in the garage on a very hot evening. The cylinder head never went above 200 degrees, and the engine coolant temp down in the block hung out around 185. And that is with only one fan working. For some reason the computer control of the fan number two will not allow me to put the temp below 200 dgrees for it's turn on. Maybe I will set it up to go on with the AC, or perhaps even put a rocker switch on the console for this fan, since it seems to stay pretty cool under normal operating conditions with just the one. I suspect when I take the top cap off tomorrow morning, I will be able to add some more coolant. Thanks for the advice, and the links.

Sam

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