radiators with no cap, and the fill bottle

[JHZR2]

Hello,

Trying to get a grasp on the cooling system in my 2004 saab 9-3. The radiator doesnt have a cap. Like most euro cars, the expansion bottle is capped, and can hold pressure. Mine has one connection going to/from the firewall, one going to the engine itself, and one going to the radiator.

The one to the radiator Im sure is for filling. The one to the engine block I assume is part of the flow path, but Im not sure why.

THe funny thing is that the hose going from the firewall to the reservoir is large in diameter - probably a 1" OD hose. The one going to the engine and the one going to the radiator are maybe 1/2" OD hoses.

OK, so maybe that makes sense... but I did not think that typically you had flow through the reservoir, even if pressurized. Am I wrong?

I give my saab as an example, but this could be a BMW, or MB vehicle too, all of which have similar systems.

Can I assume that the reservoir is part of the flow path? I never see coolant flowing... If it is, then it sure is a nice way to renew maybe 1/4 gal of coolant each time youre under the hood... that has to be a good thing!

Thanks!

 

[Steve S]

Older Fords to had a similar setup.

 

[JustinH]

Yeah its basically an overflow bottle. Most of my late 90's fords had this setup.

The cap on the overflow bottle holds pressure.

 

[rationull]

The GF's old Volvo and her current Mazda3 also have this setup. I'm not sure if the overflow is part of a flow path, but like you said I've never seen any flow when looking under the hood with the engine running.

It's an interesting question though, and now I'm curious too.

 

[440Magnum]

Jeep Cherokees from the start up until the 'HO' version of the 4.0 around 1990 used a pressurized overflow bottle system. The first-generation Chrysler LH cars (Intrepid/Concorde/Vision) from 1993 used it too. The reservoir on those vehicles was part of the flow path so that it could de-aereate the cooling system, and I assume the Saab system is similar.

 

[rationull]

Originally Posted By: 440Magnum
The reservoir on those vehicles was part of the flow path so that it could de-aereate the cooling system, and I assume the Saab system is similar.


On our old Volvo, there was a hose from the top of the thermostat cover going to the pressurized overflow bottle. If the thermostat was oriented correctly it was supposed to bleed air into the overflow bottle through that hose. I'm not sure if coolant went through that hose or not but I always assumed it was just for air.

 

[JHZR2]

Originally Posted By: 440Magnum
Jeep Cherokees from the start up until the 'HO' version of the 4.0 around 1990 used a pressurized overflow bottle system. The first-generation Chrysler LH cars (Intrepid/Concorde/Vision) from 1993 used it too. The reservoir on those vehicles was part of the flow path so that it could de-aereate the cooling system, and I assume the Saab system is similar.


Interesting... it looks like only the return from the heater core flows through... I assume no heat called for, no flow (unsure if there is a monovalve, a pump setup, or if it just flows all the time and doesnt blend).

Still, the radiator and the engine block can expand/contract in, and onl flow if need be from input via the heater core. Pressure is constant, so ou get flow, I suppose...

It is a good way to get 1/4 gallon of coolant swapped when under the hood, I guess. Why not keep those additives topped up?

Unless there is some worry about getting new, fresh air into the system... kind of like on a closed hot water system heating the house - you want old water in there as the oxygen content is lower...

 

[swalve]

Originally Posted By: rationull
Originally Posted By: 440Magnum
The reservoir on those vehicles was part of the flow path so that it could de-aereate the cooling system, and I assume the Saab system is similar.


On our old Volvo, there was a hose from the top of the thermostat cover going to the pressurized overflow bottle. If the thermostat was oriented correctly it was supposed to bleed air into the overflow bottle through that hose. I'm not sure if coolant went through that hose or not but I always assumed it was just for air.


That's how it was on my 99 Contour. Part of the reason for doing this is to allow for the radiator to be lower than the engine. I thought the system worked very well. There were a couple of small hoses that came from the top of the system and "squirted" into the reservoir. At the bottom of the reservoir, there was a larger hose that went to the same place the bottom radiator hose went into the engine. After a few minutes of operation, you were pretty much guaranteed the system would self-bleed.

Had the car for 130,000 miles and 7 years, and never had any cooling system problems. Clean as a whistle.

 

[labman]

I traded my Grand Am Quad 4 off in 02, but vaguely remember some ''Y'' shaped hose connecting the radiator, reservoir, and engine. I remember a mess when stop leak plugged the brance to the reservoir. There was flow in all the hoses all the time.

 

[Win]

Originally Posted By: JHZR2


OK, so maybe that makes sense... but I did not think that typically you had flow through the reservoir, even if pressurized. Am I wrong?

I give my saab as an example, but this could be a BMW, or MB vehicle too, all of which have similar systems.

Can I assume that the reservoir is part of the flow path? I never see coolant flowing... If it is, then it sure is a nice way to renew maybe 1/4 gal of coolant each time youre under the hood... that has to be a good thing!

Thanks!


I would assume the line going to your firewall is a pressure relief overflow vent to some point outside of the car - that's how it is on Jaguars.

The overflow reservoir is absolutely in the coolant path on my '94 Jaguar - each bank of six has its own thermostat, and you you can see the coolant flowing in the reservoir when a thermostat opens.

Not sure about the newer Jaguar, but on it and on my (former ) 04 GTO and the new G8, I assume there is at least some migration of coolant in and out of the reservoir, so I always vacuum drain the reservoir and refill it with new coolant at every oil change.

At worst, this costs a few dollars in coolant. I'm OK with that.

 

[eljefino]

Saturn s-series has this. The pipe below the surge tank has flow but the one up into the tank has very little. A 1/4" hose from the upper water outlet to the tank sees pressurized air/water vapor and burps the system. Yes if that hose blew boiling coolant could spray out but it stays dry mostly.

One is supposed to put cooling sealing tabs in the s-car; the best way to do this is to drain 1/2 gallon from the rad, making the bypass pipe below the surge tank empty. Mix a slurry of sealing tabs and 1/2 pint antifreeze, dump that in (so it gets in the "flowing" system) and top off with good AF. Many would like to just dump the seal tabs in the surge tank but this just leads to goo.

You'll note the surge tank full level is at or above the top of the cylinder heads or other vital needs-cooling devices.

 

[Drew2000]

One of the purposes of the pressurized expansion tanks that have coolant flow through them is to remove disolved air fom the coolant. Ford calls these "de-gas bottles", and it's on most/all of the newer cars.

 

[rationull]

Originally Posted By: Drew2000
One of the purposes of the pressurized expansion tanks that have coolant flow through them is to remove disolved air fom the coolant. Ford calls these "de-gas bottles", and it's on most/all of the newer cars.


So what part of the system fills that purpose on systems with non-pressurized expansion tanks? Does dissolved air only get removed from the coolant that happens to get pushed into the tank on those systems?

 

[swalve]

Originally Posted By: rationull

So what part of the system fills that purpose on systems with non-pressurized expansion tanks? Does dissolved air only get removed from the coolant that happens to get pushed into the tank on those systems?


That's my understanding. Old radiators had a tank and an air gap at the top. The next generation with the coolant recovery systems and the pressure relief cap would burp out any air that got in there (and suck back in pure coolant as they depressurized).

 

[Drew2000]

It's especially important with coolants like Dexcool. Air in the system seems to turn this junk into brown sludge.