Coolant leak in 2013 NCV3 Sprinter

We have a 2013 Mercedes Sprinter with 135k miles which had been humming along happily lately. Until the orange wall of scary messages showed the low coolant message.

We purchased some Zerex G50 coolant (50/50 mix) and topped off the coolant reservoir which had fallen below the minimum line.

About 200 miles later (3 days later) we have the low coolant sign again and I understand that likely means that we have a leak.

Other factors:
- the MB dealership performed a B service and changed the oil, oil filter and the fuel filter about 500 miles or 3 weeks ago

- we were concerned about humidity and condensation and have been running the AC + reheat dehumidifier + cabin air recirculation for the past few free days, starting before the low Coolant warning first popped up

- we have manually removed the rear cabin AC unit and capped its various pipes and hoses.

My questions are:

1. What are the components that the coolant travels to? Does the coolant have anything to do with the rear AC, front cabin AC and/or the reheat dehumidification functions?

2. Is identifying coolant leaks (no visual signs yet) a reasonable DIY project or should I head back to the dealership for yet another visit?

3. Priority: Is there an urgent risk in continuing to top off the coolant once it leaks again and thus kicking the can down the road?

Thanks for reading and any feedback would be appreciated!

Pressure test it and you should be able to locate the leak.
If it’s equipped with a rear heater - the coolant pipes do go near the diesel tank

Burkilimo said:

Pressure test it and you should be able to locate the leak.
If it’s equipped with a rear heater - the coolant pipes do go near the diesel tank

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Thanks. I understand there's a tool that auto store lend out to do this test. Right? I'll read into that and how to do the pressure test

Yes we also have a rear heater which is presumably separate from the rear AC which we removed from the roof.

The rear heater has 2 hoses going into it from underneath- drivers side near the diesel tank. Sometimes it leaks at the connection to the rear heater at this location. Place a newspaper under the front engine area after having driven it. If there is a leak you should be able to see the coolant spots.

Leaking things usually leak more over time. sometimes slowly, sometimes quickly.

If you are not capable of getting under the van with a good light and tracing coolant pipes and hoses, perhaps a visit to the dealer is in order.

But if you are up for it, coolant is circulated from the engine block, coolant pump, radiator, heater and rear heater. also to some exhaust components.

mikeme said:

Leaking things usually leak more over time. sometimes slowly, sometimes quickly.

If you are not capable of getting under the van with a good light and tracing coolant pipes and hoses, perhaps a visit to the dealer is in order.

But if you are up for it, coolant is circulated from the engine block, coolant pump, radiator, heater and rear heater. also to some exhaust components.

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Valid point. Now that I know where I need to look I'll check it out as soon as the rain takes a little break

This YouTube video helped me better understand what the coolant is and how it works as it makes its way through the engine, the radiator and the heaters.

https://youtu.be/V7inC4lOpGs

The nonstop rain finally stopped, and I think we've identified where the coolant is leaking from.

There's a valve at the bottom driver side of the radiator that it was coming from. I tried turning it and at first the coolant started to come out a lot faster but the leak didn't seem to go away completely in any valve position.

Is there a seal in there that needs to be replaced? Or should I put a cap on the fitting?

That valve should have an o-ring. Loosen it and change the o-ring

Burkilimo said:

That valve should have an o-ring. Loosen it and change the o-ring

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Thank you and happy new year!

I have little visibility under there because I haven't taken any parts out to reach the valve. It seems to turn left or right and pop in and out slightly.
When I pull it out I can see the O-ring. I'll pick up a new O-ring when the stores are open again and go from there.

SeattleNewbie said:

Thank you and happy new year!

I have little visibility under there because I haven't taken any parts out to reach the valve. It seems to turn left or right and pop in and out slightly.
When I pull it out I can see the O-ring. I'll pick up a new O-ring when the stores are open again and go from there.

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Did you get this issue fixed? I have a 2014 and my coolant warning just came on today. Hopefully its a simple fix

Loomin said:

Did you get this issue fixed? I have a 2014 and my coolant warning just came on today. Hopefully its a simple fix

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I did not because after closing and tightening the drain valve of our radiator the leaking issue has not reoccurred.

Have you identified the source of your leak? Is it the same drain valve opening?

That is the radiator drain valve/tap.

Loomin said:

Did you get this issue fixed? I have a 2014 and my coolant warning just came on today. Hopefully its a simple fix

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Over the past 10 months and 15k miles, our coolant leak happened one more time: at high altitude, in hot climate and after a long highway drive, the radiator drain valve popped open again and dumped a lot of coolant. Luckily I had the coolant to replace it and waited till we happened to visit the MB Lynnwood WA dealership yesterday.

The shop foreman inspected and replaced the drain valve plug itself because its threads were worn out. $20 or so he chuckled when I shared that another dealership's service advisor had suggested that the radiator might need to be replaced.

I'll update again if it comes up again.