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I am trying to diagnose a leak in the auxiliary cooling system of my 2014 E550. I noticed this issue because there was a leak in the main radiator for the main engine cooling system.
When this radiator leak happened, I read out the code from the engine, "M278 P026A00 error - efficiency of the charge air cooler is not sufficient". When I checked the auxiliary coolant tank, it was empty, and it seemed to be taking in liquid even after pressurizing the system with the leak detection kit. There also seem to be no leaks apart from the radiator leak and no coolant smell in the cabin. What could be the possible cause of this issue? Would the heater valve/heater core leak cause a drip? Or do you feel there is a leak in the intercooler/transmission cooler?
I would be very grateful for any advice about how to diagnose this issue.
Couple good news ...
-- The intake air charge cooler is not connected to engine coolant.
-- The cabin heater valve no longer leaks: there is none. The heater is always fully Max.
Can you inspect engine for coolant residues else use a UV die to make the leak easier to spot.
Last edited by CaliBenzDriver; Oct 30, 2024 at 02:24 AM.
Thanks for the quick response!
There doesn't seem to be any apparent leak, even when we checked the car from underneath. For some reason the previous owner filled the main cooling system with incorrect coolant (pink) but the auxiliary coolant is the correct spec (blue). We could only find pink coolant leaking from the main radiator.
I am holding off on a UV dye check because we're currently replacing the main radiator. Will report back after an update.
Pink is the new coolant, blue is the older coolant. They both CAN NOT BE MIXED.
Mine now is , engine radiator system = Pink
Aftercooler system = Blue
Your engine is M278 and has the aftercooler ( charged air cooler ) cooling system stand alone, not sharing with the engine radiator.
It is odd if the leaking radiator is the engine's one and you get a DTC as though as the heat exchanger ( baby radiator ) of the aftercooler is the one lacking performance.
Pink is the new coolant, blue is the older coolant. They both CAN NOT BE MIXED.
Mine now is , engine radiator system = Pink
Aftercooler system = Blue
Your engine is M278 and has the aftercooler ( charged air cooler ) cooling system stand alone, not sharing with the engine radiator.
It is odd if the leaking radiator is the engine's one and you get a DTC as though as the heat exchanger ( baby radiator ) of the aftercooler is the one lacking performance.
What scanner are u using ?
Currently, my coolant configuration is the same as yours: pink in the engine system and blue in the auxiliary system.
I checked the codes using my TOPDON scanner and was unable to clear the charge coolant Code with it. I had actually topped off the auxiliary cooling system six months ago and hadn't checked on it since. Back then, it was missing a small amount of coolant, but I didn't have any codes. But this time, the entire auxiliary expansion tank was empty, and even after refilling it, the coolant disappeared from the tank within 5 minutes of driving. I wasn't able to spot any leaks from underneath the car either. I am hesitant about adding more coolant in case it leaks into the intercooler. The car didn't seem particularly sluggish, though, nor did the interior smell of coolant. But it is currently waiting on a main radiator replacement before I can drive the car.
01. You will need radiator pressure tester system to troubleshoot this and also to verify all works done well.
Test at 15PSI, both the engine radiator system and the aftercooler cooling system.
I do 12 hours test sometime.
If leak is big enough at aftercooler system, as in pressure drop is say 1 PSI in 5 minutes, use a smoke tester if you have one.
Remove all 8 spark plugs to see if smoke comes out of it, which means the aftercooler is leaking between air to its coolant side.
If the aftercooler is leaking coolant to exterior and not to air intake side, the only place we can't see the coolant ( unless really a lot ) is at the V bank.
Start at 08:50
02. The only way ECM can claim that aftercooler is : "M278 P026A00 error - efficiency of the charge air cooler is not sufficient".
Is by the intake air temperature sensor compared to outside ambient air temp. When coolant is not sufficient in the aftercooler system, temperature will be higher for sure.
Without pressure tester, we can't troubleshoot minor coolant leak issues properly.
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03. I am surprised if you engine's radiator is leaking at this age, it being a 2014 should not leak yet at its radiator,
but it will leak from its dumb-azz turbo coolant lines which are plastic ...... much sooner than 10th year.
I got the main radiator replaced along with both the coolant tank caps. Unfortunately, the auxiliary cooling system is still leaking. I got it pressure tested by two indy mechanics, but both of whom couldn't find anything odd after an hour of testing.
But I did notice the cabin smelling of coolant after leaving the car parked for a couple of days. But this goes away once I start driving the car, even with the heating turned on, and the windows don't seem to be fogging up. Is it the heater valve that's leaking or is it something else?
I got the main radiator replaced along with both the coolant tank caps. Unfortunately, the auxiliary cooling system is still leaking. I got it pressure tested by two indy mechanics, but both of whom couldn't find anything odd after an hour of testing.
But I did notice the cabin smelling of coolant after leaving the car parked for a couple of days. But this goes away once I start driving the car, even with the heating turned on, and the windows don't seem to be fogging up. Is it the heater valve that's leaking or is it something else?
Cabin smelling of coolant can only comes from leaking heater core of the HVAC system.
However, the heater core is using the engine's coolant and not the charged air cooler ( auxiliary ) system.
If your heater core has the older electric valve for coolant and is still good ( no leak and solenoid is working ), unless HVAC heater is turned ON, this valve will stay close and will not allow heater core to get coolant
circulation, hence the leak was not detected when and if pressure testing is done but the HVAC heater core is not activated ( open ).
The M278 / M157 new electric valve for HVAC heater core is no more sold, now it is just a pipe without the valve....which means the heater core will always get hot coolant flow.
Which if you are like me in the tropics, this heater core having such heat is eating into our HVAC cooling power. I have disabled my HVAC heater core, I by-passed it. I do not need heater.
Now if your charged air cooler coolant side is still "leaking", how many milliliters are you loosing and based on how many hours driven ? Miles does not matter, engine hours matter.
Thanks for all the pointers! The smell of coolant in the cabin is very intermittent. I only smelt it twice after not using the car for a couple of days. I am surprised to learn that the heater core gets coolant from the main coolant loop; I don't think it was tested after the radiator was replaced.
The auxiliary coolant system has a more pronounced leak, which wasn't diagnosed after two separate pressure tests. Over the last week, the car must have been driven for a couple of hours. In that time, the auxiliary expansion tank (that sits in the engine cavity) leaked about 2cm of coolant. Do you know what the common leak points would be? We can try to test with a UV dye to see if the leak is external or inside the intercooler.
If 2 CM level gone from small baby reservoir of charged air cooler system after a few hours drive, that may not be actually a leak....yet..... if and when this cooling system been recently drained.
It could be the re-filling of the coolant is not done very well and air still trapped, thus when car in use, eventually the air bubble goes up to the coolant reservoir bottle.
Fill coolant up and monitor again, by total use of 10 hours, all air bubbles would be gone.
My equivalent charged air cooler has once develop a leak, but super small 10 drops only leak when and if the car is driven hard.
It is from the o-ring internal to the hose quick connect clip, the hose to the small baby coolant reservoir bottle.
Item #280 is the hose set I am speaking of.
This o-ring .
I have replaced all coolant hoses and all of plastic pipes handling coolant.....of the entire car this year, 10th year.
Main engines + charged air cooler.
Both coolant reservoir bottles also replaced.
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If indeed that 2 CM level coolant loss at baby reservoir is from a leak and your techy can't find it, I will say he is not doing a proper job.
Some leaks are very small and 1 hour pressure test is not enough. I told you I can do up to 12 hours pressure test.
Smoke + pressure test, but coolant must be emptied first.
Fill cooling system with smoke ( smoke machine ) at say 1-2 psi is enough. And then use the radiator pressure tester to pump it to 15 PSI.
Good smoke machine should be able to do 5 PSI.
)
