Coolant system question - real life test against theory?

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Henry has a plastic expansion tank. The only time I needed it was when tinkering with the engine running and he decided to boil his coolant.
The problem was that the vent pipe from the tank was blocked solid and the pressure blew the top off the tanks filler cap. Thankfully I was round the back when it went bang.
There is always an air gap at the top of mi rad.
 
Same set up on mine. Mine is almost full to the bottom of the lower cap seal. To test mine I used a simple wooden dipstick in the expansion tank so I could monitor level when cold and level when hot. It seems to be correctly expanding and contracting. I think the cap needs to be 9psi rated. I too had to pinch an outer cap seal from another cap I had to make a good seal on the top of the rad neck
 
I suspect that anyone who's truck has any air at all in the rad has a cap that is not sealing on the outer ring, and that the air is just acting as a expansion medium, in the same way as the 300tdi (etc)s expansion tank is set up.

Ie the user fills the rad to the top, then, on the first trip out, the water expands, and flows into the expansion tank - then on cooling, air is sucked back in (ie no coolant recovered), and then, on subsequent trips out, this air is just compressed, and the valve does not open at all.


...which i guess is all ok, but not the correct operation of the system.
 
Don't forget it's a series system, they don't really have an expansion tank, just an overflow bottle. I was always under the impression that with old style rads, the ones with twist off caps, they should only be filled to just slightly above the top plate so that when hot, the expanded coolant has somewhere to go rather than out of the rad.

Col
 
If theyre not supposed to recover the coolant, then there's no real reason for the overflow bottle - may as well be total loss.
 
Had a chance to take a photo whilst working on my Series 3 today.
Note the piece of cork I placed in the rad spout floating and the two seals on my cap.
 

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Thank you - now that's what i think they should be like.

Im going to see if i cant get a cap with the double (well, triple, if count the return valve) seal, and see what happens then.
 
julianf said:
Does yours? When you take of the cap on the rad (not the expansion tank) is it 100% full, no air at all?
Click to expand...

I’ve just put a 200di in my late series 3 keeping original rad, after redoing the pump gasket to stop a leak and refilling after a run, prob due to getting a bit more coolant into heater, I’m now getting a steady level at where the inner cap sits at bottom of neck, my cap has the two rubber seals so I’m thinking it’s working correctly and it has the correct level
 
If it is working and you do not have to top up often then it is fine. If it becomes a problem you can fit a 19j pressure tank [ not as big as later models ] but you also need a lower hose with the return connection.
What have you done about oil cooling ?
 
I’ve used original series rad hoses and no fan
I haven’t fitted the turbo or oil cooler, so blanked off the ports and removed the oil thermostat from pump housing as this could stop circulation when warm , I took it out yesterday and temp needle didn’t move off the white bit on gauge, engine seems To run quite cool which is the norm
 
In a 200 the oil does a lot of the cooling around the bottom of the pistons and if you were doing heavy towing or hard off road stuff I would recommend fitting a separate oil cooler [ does not need to be large ] For normal use your set up is fine.
I recommend fitting an aftermarket temp gauge that reads in numbered degrees so you know exactly what temperature you run at.
 
My S2A does exaclty as the OP describes. (And so it should, the effort that's gone in to getting it right..) The rad is always full to the top and I just check the expansion tank. It self bleeds. The expansion tank is old but after 50 years could still be a "later" addition. I carefully (its thin!) filed/peened the rad top face flat and got the right cap with the gasket and it works.
 
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