weird coolant issue

Greetings from Wales Jimny lovers

I know I've posted about this issue a few years ago for a different Jimny but I'm still non the wiser and have the same issue with my current 2002 one. 

My coolant does not get drawn back into the rad as the system cools down. This leaves my rad short of water and the bottle over full at best. Usually, I can lift the overflow bottle off, pour the collant out until the rad is full again and the fluid left in the bottle is at the correct level. All my Suxuki cars have done this, so 4 Jimnys and an 1.3 Ignis. This current one has done for several years (it is my wife's former car) Like them all, there are no head gasket issues, it doesn't overheat when towing (and I tow often with it and sometimes up to GTW),or when driven briskly, (nearly all the time) it has no leaks, doesn't 'steam' from the exhaust, and has never got any worse. Like the other Suzki cars I've owned, I've changed the rad, used a genuine Suziki rad cap and use good quality coolant. If they had a pressurised expansion tank, I think they would be fine.  It can't just be coincidence that the same problem exists across 5 random Suzukis. 

As an ex copper-and-brass radiator reconditioner, I have good soldering skills and am well capable of making or modifying a brass expansion tank with a pressure cap on it, but the lack of distance between the top of the rad and the bonnet will make that a problem, but not an impossible one. Before I go to the bother and hassle of undertaking this modification, I'd love to hear what others think.  Any ideas?

Thanks/Diolch

Well the most common solution is to confirm that the rubber pipe attached to the expansion bottle cap is either sufficiently long as to rest on its side on the bottom of the bottle such that the end is open or alternatively have it sufficiently short that the end can't touch the bottle keeping it again open. If it's almost touching it can work as a one way valve as the coolant contracts with the engine off. It was something I had with my 2011, though ultimately that was found to be a very mild head gasket issue after several years of diagnosis. I genuinely believe it contributed to the eventual problem, probably in conjunction with a failed viscous unit.

Make sure there are no leaks in the connections between the pipe connection on the radiator neck all the way to the bottom of the pickup tube in the expansion reservoir.

A pin hole or crack will not cause a problem for the transfer of expanding coolant, but, it will prevent the vacuum that forms in the radiator as it cools from lifting coolant out of the reservoir.

The idea, as I guess that you know, is that when cold, the radiator is filled right to the tippy top with coolant.
When hot, the coolant expands and acts against a spring valve in the radiator cap which allows the surplus to flow into the expansion tank. This also pressurises the system, and raises the boiling point.

When it cools down again, the coolant contracts back to it's original volume creating a negative pressure in the system, and allowing atmospheric pressure to push coolant back from the expansion tank through a second valve in the middle of the radiator cap.

So the radiator cap has 3 seals- 

one on the outside of the rim (1) that maintains an airtight seal to prevent liquid coming out under the rim of the cap, and air being drawn in at this point, rather than liquid from the expansion tank.

one on the pressure/expansion valve (2) that seals against the lower rim on the radiator and lifts up under spring pressure to allow coolant out into the expansion tank

One on the vacuum break/fluid in valve (3) that drops down to allow fluid back in.

If seal (1) is damaged/missing then air will be drawn in instead of fluid as it is easier.

If the vacuum break/fluid in valve is stuck, then the contraction of the fluid creates a negative pressure that will suck the hoses flat, but probably will draw some air in through the waterpump seal. Then when you open the radiator cap when it is cold there will be a hsssssp! (as opposed to a psssh!) as air rushes in, the hoses spring back and the coolant level is down.


If the head gasket is leaking, then air from the cylinders is added to the coolant, some doesn't escape into the expansion tank and when it cools down the system stays pressurised- the hoses will be firm when cold, and when you open the radiator cap it will go psssh! as air escapes out and the level will be down.

So in summary, you will have low coolant in the radiator if

1) fluid can't get back in. The hoses will be a bit flat and it will go hsssp! when you open the cap.
The radiator cap lower valve is stuck, or there is about a 0.0000000001% chance that somehow the tube in the expansion tank is right at the bottom, and is managing to seal against the tank bottom. EDIT: if the tube is kinked flat, then pressurised water might unkink it enough to let water out, but it will suck even flatter when there is negative pressure in the radiator.

2) Air can be drawn in in preference to liquid, seal (1) is not sealing, or there is a slight air leak somewhere in the pipe to the expansion tank, or the waterpump seal is failing.

3) air is being pushed into the system from a headgasket weep. the hoses will be firm when cold, and it will go psssh! when you open the radiator cap.


 
 

Thanks for your detailed explanation of things, espcially of the rad cap. I'll check and re-check. Just bloomin odd that all my Suzuki cars have had this issue from the get-go. Thankfully, my Suzuki LS 650 motorbike is air-cooled!

Thanks. I haven't checked the pipe itself for leaks, so definitely worth a go