Coolant level in radiator!

[Leo]

Hi,

Quick question! Everytime I check the coolant level in my radiator (not the overfill reservoir) when the engine is cold, there is barely enough coolant covering the core. If I fill it up again, heat cycle the engine, it dissappears again, presumably into the overflow tank.

My understanding is that as the motor cools down, its supposed to pull coolant from the reservoir tank back into the radiator itself and my car isn't doing that. Is it a problem? I've replaced the radiator cap, and it does not seem to solve anything... Btw the car does not use any coolant 'per se'.

Thanks!

 

[HerkyJim]

What kind of car? How many times have you refuilled the radiator? Seems like the coolant should be overflowing the external reservoir by now. Where's it going? Check for coolant in the oil?
it should work this way...there should be airtightness in the whole cooling system except the radiator cap and the fill/overflow of the reservoir. AS the coolant expands with increasing temperature, the check valve in the radiator cap is opened (approx 16 psi or so) and fluid flows to the reservoir. As the coolant cools down, the fluid contracts and fluid flows from the reservoir back to the radiator through another valve in the radiator cap. Assuming no leaks, you shouldn't have to open the radiator cap. Just check coolant level in the reservoir. It should be maintained at or slightly above the ADD/MINIMUM level. If you were to fill the radiator and reservoir when cold, tghe resrvoir would have to overflow due to expansion when the engine heated up.

If you have a bad radiator cap or say a cracked filler neck or leak in the line between the radiator and reservoir, you could be losing fluid. If you have to run without a functioning reservoir, the coolant level in the radiator will have to be considerably less than full whn checked cold, in order that there would be room for expansion. This is bad because you don't want contact between coolant and air or you may get sludge/corrosion/problems

see http://www.troubleshooters.com/tpromag/200204/200204.htm#_how_cooling_systems_work

goodluck, my $0.02

 

[Leo]

Hi HerkyJim. Thanks for your reply.

I was meant to say the quantity I put into the radiator ends up in the overflow reservoir after the motor warms up; it then does not get sucked up again when the motor cools. So maybe the valve in the radiator cap is stuffed, and does not let the coolant back in? The motor does not use coolant because I just take the coolant from the reservoir and put it back in the radiator. No loss anywhere..

I'll take another look. Might have to buy a genuine radiator cap or something, because I replaced it with a cheapie one not long ago (seals were stuffed on the old one).

Thanks!

 

[Gary Allan]

If you've got air in your rad ..and no net lose of coolant ..and your system had full integrity ..then you hoses should be somewhat collapsed on cold start. Air has to be getting back into it somehow ..and it's easier for it to get in there then it is to draw the coolant from the resevour.


Check all your clamps just for the heck of it ...and take a look at the hose between the rad cap and the resevour tank in particular. The pushing "out" may end up in the tank ..while the uptake of the coolant may be in competition with a very small air leak that appears a no brainer when comparing sucking in air as opposed to lifting a water column (siphon is broken).

 

[The_Jeff]

If the overflow bottle is lower than the level of the radiator cap there will be a slight vacuum in the radiator when it's cold. It will suck some coolant back if that vacuum gets high enough and the cap and system work ok, but it has to draw the coolant uphill. You're going to wind up with a minor "air space" under the cap. Do you get any whoosh or gurgle when you open the cap?

I'd just drive the car for a week without touching a thing then mark the cold line on the overflow bottle with a magic marker. Then check it after driving; the level should be up. When it cools back down it should find your mark.

 

[blupupher]

Yea, I would try another cap. Sounds like it is letting air in around the cap and not letting it suck the coolant back in.

 

[Leo]

Thanks for the replies guys! I think I figured it out. The hose from the reservoir cap that goes to the bottom of the reservoir is stuffed. It was leaking from the base of the reservoir cap! So the engine was just sucking up air as it cooled down and not the coolant, because there was no 'woosh' to indicate any vacuum present. I'll heat cycle the engine tomorrow and see how it turns out...