Radiator Fluid Top Up

[cmartyn]

I noticed when I bought my Rogue (21 SV) 4cyl 2.4 that there doesn't appear to be a radiator cap. The coolant reservoir was alittle above min and seemed to stay there for the last three years. Finally decided to fill it back to maximum like the owners manual says. And now, only 2 weeks and about 50.miles I notice it's gone down about 1/4 inch. I know that's not a lot of fluid but it says fill it to the max line when cold. Should I keep.doing that or will.it just keep disappearing? It's a sealed system right? When it heats up.is there somewhere for it to go? If it were to boil over what happens with no radiator cap?

[VStar650CL]

The reservoir is pressurized, like a lot of recent Nissan products. Under normal circumstances the reservoir should only be at or near max with the engine warm. It should be someplace in the middle cold. The only time you fill it to max is when bleeding air from the system, you warm it up, fill it to max, then let it cool. Air gets expelled into the reservoir through the pressure valve each time the engine warms, then as it cools the vacuum valve allows fresh fluid in to supplant the air. You repeat that until the level in the bottle no longer drops.

A bit of air in the system after 3 years is normal, and you should let it stabilize between min and max, not keep filling it to the top. If you keep losing that same 1/4" repeatedly after it stabilizes in the middle, then you may have a small leak.

[cmartyn]

Ok.. it seemed to stabilize at the min line for 3 years or so.. The manual.says to fill.it to max when it's cold. I dunno. Its between min and max now. Closer to max so I'll just keep an.eye on it for now. Its definately got pressure in there. Even after sitting for four days it expelled air opening the cap.

[VStar650CL]

If it holds pressure for days then it certainly isn't leaking. Keeping it filled to max when cold will sort of create a leak, because there's noplace for the excess coolant to go when the pressure rises. So it will dribble out through the overflow passage until the level drops to a point where it isn't overfull.

[cmartyn]

Do you know where that passage is / goes? I see two hoses that go in there a big one and a little one.. but man it's so cold out I have to admit I didn't look too hard.

[VStar650CL]

IIRC on the gen3's it's molded into the tank.

[cmartyn]

Well.. I went over it.prety good, I don't see anything. There is the overflow pipe.. 3/8 od or.so.it goes to a little pipe tapped into.the upper radiator hose. Then there is the larger 5/8 od or so tube that goes into the bottom of the rad. I don't see any signs of fluid discharge. No radiator cap. I bet if it boiled over it would just pop a hose or something.

[cmartyn]

First drive in a few days. Checked the level hot and it was just below max line. This morning it looks do be down where it was. I'll keep watch on it. I don't see a pressure releif valve on the expansion tank anywhere,could it be part of the cap? Also, you mentioned a vacume releif valve that is responsible for letting air into the system when the fluid cools. Where is that located in this system?

Also, happy new year!

[VStar650CL]

Yah, could be in the cap. That's where it is on a normal system, both pressure and vacuum.

[cmartyn]

So, it's totally sealed then. Unless there is a massive air bubble, the 1/4 inch of fluid movement up and down with a slight loss over a long period would be normal.

Thanks again.

And happy new year!

[VStar650CL]

Unless there is a massive air bubble, the 1/4 inch of fluid movement up and down with a slight loss over a long period would be normal.

Correct. Happy New Year to you as well!