Coolant Loss How much is normal

I have Subaru WRX with 57k. My heat is a bit weak at idle (below 2000RPM) blowing cool air and very hot about 2500RPM.

Checked the coolant in bottle as I could see any in the bottle from the side and I heard a air hiss when opening cap. Now the heat has improved. At warm engine the coolant bottle is below the cold mark. I plan on adding some, likely a cup or two.

Is a cup or two considered “normal” over 28k miles since last coolant change? What is normal tolerance?

[b]Andrew, I would say that it depends … [/b]

It depends on whether the cup or two was lost over the entire 28,000 miles, which would be normal or lost over just the last few thousand miles of the 28,000, which may indicate a problem. It needs to be monitored regularly to see if there is a recent steady or fairly rapid loss.

The heat shouldn’t fluctuate from cool to hot with a change in engine RPM. The system is designed with a thermostat to keep the temperature relatively constant. By the way, what year is the vehicle?

The coolant loss I believe was likely over the entire time assuming it was filled properly. I assume yes as heat was fine until late last winter and definitely this winter.

Back at 28k(currently 57k) I had the dealer verify the coolant level and it was similarly down. Checked for leaks and none found(under warranty). I was replaced as scheduled at ~30k.

The car is a 2004 and still under powetrain warranty for 4 more months 3k miles. Unfortunately this only covers water pump/gaskets and not radiator itself.

In my case it depends on the car. I had a 98 Windstar that used to lose a pint of coolant a month. The mechanic verified it wasn’t a head or intake manifold gasket leak. His guess was seepage through the side tank/radiator gasket (the side tanks were crimped onto the radiator). After a few years the coolant leak stopped on its own. After 8 years, I sold the van in 2006 with 99k miles and it was running strong.

On the other hand, my 2000 Blazer started losing coolant after a coolant change at ~45k miles. It turned out to be a leaky intake manifold gasket. During an oil change my mechanic saw a little coolant as the last of the oil drained out of the pan.

Finally, the coolant level on my 2006 Sienna, 1993 Caprice, and 1995 Dakota does not drop between changes (~3 years).

I would have the oil checked for any coolant contamination, it might not hurt to replace the radiator cap if it’s not holding pressure.

Ed B.

Normal??? Any time I see a drop in coolant then something is wrong. This is a closed system. There shouldn’t be any loss. I check mine about 3-4 times a year and change it every other year…It’s on full every time I check. Not a drop lost.

It could be a slow leak someplace…hopefully external. If it’s low then it’s leaking someplace.

There should be NO loss of coolant under normal conditions. If your car is losing coolant there is a leak somewhere. Could be internal, could be external, but there’s a leak.

If the coolant system for the 04 WRX is the same as it is for the 06 Outbacks, a cup or two of coolant loss over 28k miles is normal. This isn’t truly a closed system. There is a gap around the return hose from the radiator where it enters the reservoir bottle, and under high temperatures this gap easily allows for the loss of 1 or 2 cups of coolant over 28k miles due to simple evaporation. As I said though, this is assuming the Outback and the WRX have the same setup.

If the WRX does have a true closed system, then you might have a problem, especially since the temperature fluctuation of the air coming out of your vents is a little puzzling and wouldn’t be expected if the loss was simply from evaporation. If nothing else, you could bring the car in to the dealer to have it pressure tested again just for some peace of mind. You can also find lots of info about this issue at and

I will refill it and see what transpires. You confirm what I thought really should all stay inside the system. The system has a few more points to go wrong with a top reservoir (own radiator cap) and lines to turbo.

It has been honestly 3.5 years since it was last replaced/filled(30k miles) and checked.

Make mine another vote for checking into any measurable loss. The only path to the outside world for coolant mix to vaporize through should be the pinhole vent in your reservoire cap. The amount that vaporizes through there should be truely inconsequential even over the long term.

In all the years of driving (I’m 61 now) I have never had a car that lost coolant, other than when there was a problem. That said if you are loosing coolant and you KNOW it is not going into the engine or the oil, and it is a very small amount and is not getting worse, I would suggest you can continue watching and refilling. Personally I would have someone put pressure on the system and find out exactly what is going on and fix it.

If it is going into the engine or the oil, you have a problem that is going to get bigger and a lot more expensive. If it is leaking into the heater system (do you sometimes smell something sweet?) then you might let it go for a while, but I would not unless it was already a junker.

FYI: Some Cars Have A Closed Coolant Recovery System And Some Don’t.

I have some of each in my driveway. The reservoirs on the “closed” recovery system cars have a raditor type cap on them. My cars with an “open” recovery system just have plastic reservoir caps and the caps or the reservoirs (I have both styles) have large vents to the ambient air.

I expect my “closed” system cars to lose no coolant. However, I expect my “open” system cars to lose some to evaporation. It’s not a big deal.

Of course all my cars have pressurized cooling systems, it’s just the recovery reservoirs I’m talking about.

Additional FYI: I just checked one of my “open” system car’s Owner’s Manual. It states, "If you have to add coolant more than four times a year, have your dealer check your cooling system."
I seldom have to add any at all.

Another observation: Over the years I have noticed that the “closed” system cars do have their coolant level drop a little in the reservoir with the onset of winter temperatures every year just about the time I have to “plump up” the tyres. These vehicles have never had cooling system problems in hundreds of thousands of miles. This is just normal when our temperatures hit -20F to -30F (-30C to -35C} in the season. My first reaction is usually one of concern, but I have grown accustomed to it by now and realize what’s going on and sometimes I give them a little sip. Even some human body parts shrink a little around here in January.

In my opinion, no coolant loss is normal. I admit, though, that I am not familiar with your make and model. I would get the cooling system thoroughly checked.

If you are nervous about finding any subtle leaks before the warranty period closes, sign out a pressure tester at an auto parts store and find out how to use it. It is not complicated.

I’m in the camp that cooling systems shouldn’t lose water. Can someone explain to me or point me at an explanation for the kind of cooling system that is designed to lose water? I’d be interested in understanding it.

i don’t know either i bought dodge dakota a year ago from a dealer and the heat didn’t work very good it still doesnt and theirs a coolant leak somewhere too

Joe, Read My “FYI” Post Above.

Note what my Owner’s Manual advises.

I did read your post. It doesn’t explain what an “open” system and how it’s designed to lose coolant.

It Isn’t Designed To Lose Coolant, It Is Designed With A Pressure-Less Recovery Reservoir.

This system allows a small amount of coolant to be lost to evaporation.

Here’s my version of an explanation.
The cooling system has a radiator, radiator cap, and all other coventional components. When the system goes above normal pressure, with expanding coolant volume, like when the engine is at full operating temperature and is shut off, excess coolant by-passes the radiator cap and flows through a tube and empties into the top of the plastic recovery reservoir which can go to “full hot” level. The tank is not under pressure and vents to outside air. It’s just a plastic jug. As the engine is cooling back down, a vacuum is created in the cooling system as the coolant returns to its ambient temperature. The void the vacuum is creating is filled by coolant being drawn from a tube attached at the lowest point of the recovery reservoir and the level goes back to “cold full”. Because the “spare” coolant in the reservoir is vented to the sky, it can suffer evaporation loss.


Thanks CSA:
That’s how I too understand cooling systems of today function. It brings up a question:

In the discussion here of “open” vs “closed” systems, are you calling that an open or a closed system? (I had never heard open vs closed in the context of automotive radiator systems.)

In that kind of system, I don’t consider coolant lose normal.

I Have Described The Open Recovery System, As Requested.

My cars with a “closed” recovery system don’t have a cap on the radiator. The only “radiator cap” is actually a “recovery tank cap”. The reservoir on these cars is under pressure and only vents to the outside if they become over-full. Both systems basically do the same thing, keeping the cooling system full of coolant, while keeping air out.

Because the “open” system is vented all the time (the caps don’t even seal.), evaporation is possible and that’s why my manual states, "If you have to add coolant more than four times a year, have your dealer check the cooling system."
In this case the manufacturer considers some coolant loss as normal. I do too.

One of the regular pros on this site can correct me but I think the difference in the two systems go hand-in-hand with the difference between “conventional flow” and “reverse flow” cooling systems.

I ran across a good link to Cooling System Service