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So out of nowhere I have to keep adding coolant every couple days it be almost empty, there no leaks I can see, don't think it head gasket it's not overheating, heat works fine, engine oil color it should be, no loss of engine power, but I did just notice some like brown/orange bubbles in reservoir but I read that could be rust and need to do a flush but I can not figure out why it losing so much coolant, any suggestions? Thank you
Either it's a liquid leak that you just haven't found, or it's a vapor leak. If it's a vapor leak, it's most likely the cap. I bought myself a pressure tester from Vevor a few months ago ago and now I can pressure test my system on a regular basis. This gives me peace of mind that I don't have a leak in the o-rings of my crossover pipe inside the timing cover or the oil cooler.
So out of nowhere I have to keep adding coolant every couple days it be almost empty, there no leaks I can see, don't think it head gasket it's not overheating, heat works fine, engine oil color it should be, no loss of engine power, but I did just notice some like brown/orange bubbles in reservoir but I read that could be rust and need to do a flush but I can not figure out why it losing so much coolant, any suggestions? Thank you
A big leak is productive...
if its not going into engine/tranny then IT'S COMING OUT:
look at the radiator side crimp area all around.
If its the cap it's usually not that severe. I would inspect the radiator end tanks (the plastic to metal junction on the sides of hte radiator) oil cooler, thermostat, reservoir, and water pump. At this age it's definitely one of them. Thermostats are a bit fragile on these and tend to blow the gasket before the electrical fault starts
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Rust in the cooling system? I had a 2004 SL500 that was 17 years old when I traded it and had no rust. Confirm you DON'T have a head gasket problem by doing a block check. This test kit absolutely works if you have any kind of leak.
(LOL! It's not battery powered.)
Last edited by JettaRed; Jan 17, 2025 at 07:30 AM.
So out of nowhere I have to keep adding coolant every couple days it be almost empty, there no leaks I can see, don't think it head gasket it's not overheating, heat works fine, engine oil color it should be, no loss of engine power, but I did just notice some like brown/orange bubbles in reservoir but I read that could be rust and need to do a flush but I can not figure out why it losing so much coolant, any suggestions? Thank you
If it is not leaking out of the engine then it is leaking internally. This could be head gasket and if you see something funny in the coolant reservoir, I would really look into this.
I assume you keep adding coolant and not just water, right? Too low coolant boiling point will make it boil out. This would be leaking out of the engine though and you should be able to see something leaking out around the reservoir.
If it is head gasket you should see "mayonnaise" under the oil fill cap and should see bubbles in the coolant reservoir when engine runs.
If it is not the above, then it is leaking somehow internally and one place it can happen is the transmission cooler that is built inside the bottom part of the radiator in front of the car. If cooling system pressure is higher than the ATF cooling circuit the coolant will enter the transmission cooling system if there is a leak with this heat exchanger. To check for this is to have car level on a lift and remove the transmission drain/fill plug. If coolant has entered in the transmission you will have fluid coming out. You should have very little or none come out at 80C temperature if the transmission is filled correctly and, of course, the level setting tube at the opening is correctly in place.
So out of nowhere I have to keep adding coolant every couple days it be almost empty, there no leaks I can see, don't think it head gasket it's not overheating, heat works fine, engine oil color it should be, no loss of engine power, but I did just notice some like brown/orange bubbles in reservoir but I read that could be rust and need to do a flush but I can not figure out why it losing so much coolant, any suggestions? Thank you
For me - it was old coolant pipes...a BAD thermostat....and over pressure pushed out the temp sensor and it was leaking there as well. Granted, not the same engine in that car. On my 3.5 car I have only ever had leaks from the tank itself (no turbos to fiddle with).
So out of nowhere I have to keep adding coolant every couple days it be almost empty, there no leaks I can see, don't think it head gasket it's not overheating, heat works fine, engine oil color it should be, no loss of engine power, but I did just notice some like brown/orange bubbles in reservoir but I read that could be rust and need to do a flush but I can not figure out why it losing so much coolant, any suggestions? Thank you
Need to pressure test. ON a GL model the leak was at the neck of the fill pipe attachment.
There was no liquid visible until the pressure check. Of course, could be leaking elsewhere.
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