To begin with , Nissan Cedric, the coolant system . This is what we want to see , this picture  explains exactly what the coolant moves between the reservoir tank and the radiator. We see the allows at the tube vice versa , and the radiator cap looks non pressure type , and the reservoir tank cap looks pressure type.

This is excerpted from the L20A and L24 Nov 1969 manual .

Also pictures from an owner’s manual of 

Nov 1969 Nissan Cedric.

More to come .

Kats

Edited August 18, 20186 yr by kats

Kats, I have a 1968 factory manual for the (pre-'A') L20 six which has a nice layout drawing for the H130 Cedric's engine. It shows our early-type 'reservoir bottle' plumbed into the top hose area, a long way from the radiator cap. Clearly any pressure-relief type radiator cap that might be fitted on that particular model did not affect the function of the reservoir bottle system:

 

 

   

Thanks Alan , it  is a nice picture !

Back to this picture, what would have been like if there are two pressure relief type caps , on the radiator and the reservoir tank ? Now my Z432 is just like that , two pressure relief type caps.

In my Z432 , can the coolant retun to the radiator when the coolant cooled down ? I have never driven my Z432 so hard , then I really do not know what would happen when the radiator overflowing.

And my guess is , there would have been a pressure relief type cap only , would not have been a simple sealing cap. 

Because 21430-E4201 is the only part number for Z432/432R , and this is the pressure relief type cap . 

Kats

Edited August 18, 20186 yr by kats

Kats, I haven't been able to follow the part numbers, but all three of these caps appear to have the check valve which allows coolant to flow back into the radiator from the overflow can when the engine cools off and draws a vacuum.

37 minutes ago, kats said:

I'm not sure it will add anything to the discussion, but I did a little radiator cap repair work on my 280. Here's a pic of the cap disassembled. The inside (usually hidden side) if the check valve is in the upper left corner:

Thanks Captain ! I did not know there is a check valve , so , even in my set up ( two pressure relief caps ) , coolant can flow back to the radiator as long as the reservoir tank is pressurized.

I want to hear depressurized sound on the reservoir tank, but every time I pushed the botton, nothing happened . I wonder my Z432's reservoir tank is operating correct or not .

The Fairlady Z manual says " looking at the reservoir tank from outside , to see if the coolant level is sufficient, half of the tank " this instruction is the same for the early type and later plastic cap type .

 

I think we are on the same page there. 

But for Kats' installation on his blue HLS30U, he is using the later type reservoir bottle and that means an unpressurised bottle, one-way system. It looks to me as though Kats is getting quite a lot of coolant in the reservoir bottle. More than I would have expected. Japan has been pretty hot (to say the least!) lately, so maybe the cooling system is struggling to keep up?

Kats, is the pressure rating on your 240Z's radiator cap quite low?

 

• Thanks
• Haha
• Confused
• Sad

Alan , I just poured too much into the reservoir tank, I tried to let the coolant flowed back into the radiator using gravity !

But yes , my blue L24 is struggling in the high temp , I saw coolant level became higher than that of before driving.

Kats

Edited August 18, 20186 yr by kats

Manuals , Fairlady Z manual for Japanese customers, and I have a very rare Fairlady Z manual written in English .

Kats

It's not pressure in the overflow bottle that sends coolant back to the radiator. It's vacuum in the main radiator as it cools that sucks the coolant back to the radiator.

Thanks w3wikes, no need be pressurized, 

but need to be sealed at the reservoir tank ? 

Kats

I wouldn't think you'd want the overflow reservoir sealed. If it were sealed it could interfere with the radiators vacuum as it cooled making it harder to suck the coolant from the reservoir back to the radiator.

Edited August 19, 20186 yr by w3wilkes

3 hours ago, w3wilkes said:

I wouldn't think you'd want the overflow reservoir sealed. If it were sealed it could interfere with the radiators vacuum as it cooled making it harder to suck the coolant from the reservoir back to the radiator.

You are right, the tank must have a little opening for helping suction, that is a check valve for the metal cap , and a tiny hole for the plastic cap .

I drove my Z432 today , and i checked the reservoir tank , I see the coolant level raised about one inch before the driving.

Engine operated normally, no hard driving, I now have a STD about the coolant level .

Seeing my Z432 , two pressure relief type caps are working without any problem .

I thank you all for the useful inputs here , I am learning and I need to amend some of my comments. 

So now , Why my Blue 240Z’s reservoir tank has air in the tube ? Looks like the coolant does not flow back to the radiator . The radiator cap is a new , and is a  pressure relief type .It must  be operational for both ways , let the coolant go out , and back in .

Becaues of the radiator is not fully filled? Or there might be some cracks  in the tube ? I need to check, it is interesting !

Kats

After asking some of my friends about this , I tend to think there was a simple sealing type cap which was is used for the Z432 . 

I said 21430-E4201 was the only part number for the Z432 radiator cap from the beginning to the end , but this may not be correct reviewing the Nov 1969 Fairlady parts catalog ( 1st issued ) .

The catalog listed only Assy Radiator, not mentioned about the radiator cap which is used on the radiator. This indicates we might  have chance to have a certain part number for the cap . Just they did not show it in the first catalog .

2nd issued parts catalog is dated 03/1970 , as it is said later , the cap for the reservoir tank was replaced new one ( plastic) from Jan 1970 . We see 21430-E4201 for the first time in this 2nd issued catalog , 

also it is still listing 21430-E4200 ( cap push , reservoir ) , without mentioning a new plastic cap (21516-C0500) .

but ironically at the production line , workers put plastic cap for the reservoir tank when this catalog was issued .

So , I think there would be a simple sealing type cap there , maybe sharing with other models , and we know , parts catalog is not always correct and updated .

I found a cap at the Rallye Datsun Roadster, I think this might be the one “ simple sealing type cap “ , as not showing “ A9 “ on the right hand side like a pressure relief type cap .

And at the center part , the round rivet is different from the pressure relief type cap . 

Kats

Edited August 19, 20186 yr by kats

The type of cap that really belongs on the radiator depends on whether the plastic overflow container in intended to be a pressure vessel or not. Based on the domed end shape and the thick walls of the plastic container you have, it looks like it may be capable of holding the system pressure, but the plastic cap you have on the tank looks like it has a small vent hole in the center:

So if that is really a vent hole in the plastic cap (and it is the correct cap for the plastic container), then you should be using a radiator cap like the ones you pictured before:

In other words... Somewhere in the system, you need to contain the pressure up to the rating of a cap (for example) 13 psi. And if you're not containing that pressure with a spring loaded radiator cap, then you need to do it at the plastic tank. But you would need a sealed cap there that included a pressure relief.

I'm resisting describing how a typical system is supposed to work because I'm sure you already know all that and I don't want to explain a whole bunch of stuff you know already. But if you want, I can whip up some sketches, etc. to try to describe that.