Have you guys tried to increase the coolant capacity by using those "modern-car" setups with a bottle outside the rad tank in adition to full rad tank capacity? I mean, those "overflow" kinda bottles?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

You might want to try Zerex racing super coolant, it has no anti-freeze properties but is reported to increase cooling efficiency over antifreeze by 25%.

If you do an aftermarket conversion to a coolant recovery system, remember to drop your rad cap pressure down to 9lbs? or thereabouts and fill the rad completely to the top.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Why would you want to do that (9 lb cap)???? Factory still used a 16 pound cap with coolant recovery.
The important thing for the coolant recovery system is to get a cap with the free-hanging little valve in the middle. Non-coolant recovery systems still need to use a radiator cap that has that little poppet held shut with a light spring. STANT supplies either one now to the best of my knowledge.

The OEM radiator caps from your Chrysler dealer used to be all stainless steel. I dont' know what they are now that prouction has switched to MEXICO. Now the new OEM caps have 4 little tabs on them instead of the two like they've had for years. Yucky.

Wait, that's right, I did this on another car because I changed the thermostat setting, not because I added an overflow bottle. Disregard this.
That I do have to argue, any rad cap with the vacuum valve dangling free has a broken spring and needs to be replaced. With the valve hanging open it will not build any pressure in the system.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Usually 14 pounds on the cars without A/C or HDC.
Not correct. Both types of center valve are used on both recovery and non-recovery systems. Chrysler's rad caps had the free-hanging valve clear on up into the early '90s, at which point the spring-loaded type began appearing on Mopars.

The difference between free-hanging and spring-loaded centre valve isn't whether the cooling system has a recovery tank or not. Rather, it's to do with the design of the cooling system: Partial-pressure (free-hanging valve) vs. full-pressure (spring-loaded valve).



In a partial-pressure system, the cooling system does not become pressurised until the system becomes sufficiently hot that the coolant and/or steam wants to rush out of the filler neck. At that point, the coolant trying to flow out of the radiator closes the cap's centre valve, and system pressure builds. It continues to do so until the cap's pressure rating is reached, at which point the cap's main valvespring is compressed and coolant flows out of the filler neck via the overflow tube.

A full-pressure system begins building pressure as soon as the coolant begins to heat up, and retains it long after coolant outflow would cease to push closed a free-hanging centre valve. This can offer increased protection against localised boiling in the system, which can be necessary in engines prone to such. However, the cost is greatly increased physical stress on the entire cooling system -- hose junctions, seals, solder joints in the radiator and heater core, etc.


No, the relevant difference is that a cap for a recovery system has two rubber seals: One on the face of the main valve, which seals against the lower flange ring of the radiator neck, and another larger one just under the cap's underside, which seals against the upper flange ring of the radiator neck. The upper ring's seal against the upper flange means that when the system cools down and coolant volume in the radiator decreases, the resultant suction is channeled via the open centre valve through the overflow tube, which draws coolant from the reserve tank back into the radiator.

A cap intended for a non-recovery system has only the lower seal, no upper seal. When the system cools and volume decreases, the centre valve opens and admits air to the system.

There's no problem using a dual-seal cap without a recovery tank, but a recovery tank won't be of any use if your radiator cap hasn't got the upper ring in addition to the lower one.

So, leaving aside the pressure rating differences, and the physical differences (shape, size, length of centre stem, etc.) there are four different types of cap:

With lower ring only, with free-hanging centre valve (Partial-pressure, open system)

With lower and upper ring, with free-hanging centre valve (Partial-pressure, coolant recovery system)

With lower ring only, with spring-loaded centre valve (Full-pressure, open system)

With lower and upper ring, with spring-loaded centre valve (Full-pressure, coolant recovery system).
Chrysler's radiator caps have been very well made in Mexico for well over 12 years now. They're just fine. There are many types, made out of perfectly fine mixes of stainless steel, brass, and plastic.
Those caps aren't applicable to our old cars. Their pressure ratings are too high and they're full-pressure.

Here's a snapshot from the factory service manual.

Not mentioned, but I believe the free-hanging valve will also help purge air from the cooling system provided there are no leaks anywhere.

Adding a coolant reserve system is easy, all you need is the coolant reserve tank and the correct radiator cap (see above). But...what's the goal? The system doesn't really increase useful coolant capacity. It just keeps the radiator full. If you're trying for better cooling, you'd want to look at a higher-efficiency radiator core with more rows of tubes, or more/smaller tubes and fins, or both.

Thanks for the rundown on caps, Dan and others. Good info there.

Lou

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Home of Slant6-powered fun machines since 1988

That is a new one on me

I have NEVER seen a new cap with a free dangling vacuum valve. I have also never seen a diagram for such a rad cap before. I have found caps on lift trucks with the valve hanging, ordered genuine factory replacements, and without fail every new one has been spring loaded. I will certainly look closer now.

So my question now is, how does one determine whether a vehicle's cooling system is designed for a free-hanging vacuum valve, or spring loaded? I have never seen such information in a service manual. We are having a problem with Nissan H02 trucks blowing their upper rad tanks and their caps are all spring loaded.

Craig, there was no need for the condescending remark, I wasnt taking a shot at you. and I dont see anything in your JPG related to a free hanging valve other than a spring missing in the drawing. so it's no wonder I missed it. We are all adults here. I was wrong. Personally I am glad we got to the truth of the matter rather than this post slipping under the radar.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Original factory service manual usually says one way or the other. In the case of Mopars from the dawn of pressure caps clear on up to the last of the K-car derivatives, the answer is "free hanging". (LH cars were the first Mopars to use spring loaded).
You have nothing to lose by attempting a fix with partial-pressure caps instead of the full-pressure ones you're using now!
My Stant specbook went away long, long ago. I'll try to dig up a replacement source of info for you. Are you using an aftermarket cap now, or a factory part?
YOU TAKE THAT BACK! NOOOOOOOOOO!!!!!! *kick* *scream*

Dan,

Our Nissan caps are right from the factory that way. They are rated for 0.9 BAR (14PSI by my guess) and have coolant recovery. There is no information on the caps in the manual, only specifies to pressure test it once a year (which would be near impossible to do with a free hanging valve unless you grease it and test it upside down. I wonder how many caps got thrown out on that basis? Ive done at least 12 in 5 years.) Also, how would one know if the valve is supposed to hang or is just broken. What would the consequences be on a full pressure system? Could I conceivably damage a lift truck by retrofitting one of these caps?... Or will the bottle just boil over. I remember my 94 Ram van with a V6 had a dangling valve, and I found it diagnosing a local boil and overheat problem. I put a 14PSI spring loaded cap in and didnt have any problems afterward. Was it just running lean? Maybe... but it passed emissions...

A manufacturer specbook would be awesome. I am very interested in learning the proper selection and application of rad caps, based on pressure rating and vacuum valve. If I am lucky enough to have a lift truck's manual in my van, it never goes into real detail about the cap so if there is any way to assess the cooling system and deduce what cap to use, I would be applying that knowledge almost daily.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Seconded--Holy COW!! I had no idea there was so much to know about a coolant cap!

MJ

Let's start from the other end. Can you get me an aftermarket (pref Stant) number for your application, and I can work from there to cross it to a partial-pressure cap?

No, the truck won't overboil as long as the pressure rating is correct. Remember, both types of cap allow the same amount of pressure to build in the system -- it's just that the partial-pressure type allows that pressure to build only when it's actively needed for boil control. 0.9 bar is approx 13 pounds. Yes, you have to test the partial-pressure caps upside down, but greasing isn't necessary.

The loading springs for the spring-loaded centre valves seldom fail, IME.

To effectively add cooling capacity you need a greater volume of coolant and or more surface area for the coolant to loose heat. wider rad with larger tanks and or more rows or cores, 3 or 4 cores vs 2 rows most commonly found. I have an overflow bottle on mine but that is purely to pass tech inspection.
Also water is a much better coolant(better cooling capacity) but has a lower boiling point and will not protect at the temperature extremes.

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I could get an SMH or TotalSource number, but we usually deal with distributors only. I doubt they would cooperate with me to that end. But I do think I would be able to find a match based on their custom catalog, which lists numbers by spec of the cap itself. I dont need you to do that homework for me, though I do appreciate the offer.

It sounds like a good idea. I will research it and see if I cant suggest it to management. It could potentially save us a lot of money. Thank you!

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.