I have Peugeot Boxer van (435 onnicar) and its radiator coolant drains too fast(in one day, it's already empty). I.e. In the morning, if I fill up with water and at half of the day it's almost drain. The coolant itself is not getting hot but when you open the coolant after 2h of turn off the vehicle, while you opening, it behaves like when you open new Coca-Cola bottle after shaking a lot and lot and all the "gas" comes out. I don't know what this reaction is called but hope I "explained" it.

When the tap is completely opened, the water start coming back to the the coolant, somewhere from the tubes 🥴🥴🥴 and then goes down again.

I showed two mechanics and both of them said different things.

  • The first one says, we have to open the engine because too much pressure is becoming in the motor and some ""alignment"" has to be done in the engine and also straps/chain has to be replace.

This mechanic has also replaced the radiator 5 months ago because it was broken for some well known reason. I am suspicious about it because the problem could be in the radiator and he doesn't want to admit it. (The radiator was not new, he took from somewhere and put it on my vehicle)

  • The second mechanic said, that we need to replace the (Thermostat) and clean the radiator and the problem should be fixed.

Both mechanics showed me the water coming from the radiator to the coolant tank was not flowing continuously. Water was coming sometime, and some time doesn't. (Due to the pressure or something, maybe)

The water pipe coming from the engine to the coolant tank was flowing continuously, and the water was hot. (which seems to be correct)

Now I am confused, who should I follow.


I think, it's draining too fast due to overheat.

  • Welcome to the site. It isn't clear from your question what is happening to your coolant. Does your coolant overheat and boil over, or is it leaking out of a hole?
    – GdD
    Commented May 19, 2022 at 8:28
  • Coolant is not leaking... maybe something wrong in the radiator or engine? Maybe the engine is making a lot of pressure...
    – Phoenix404
    Commented May 19, 2022 at 9:59
  • You say coolant is draining too fast, what do you mean?
    – GdD
    Commented May 19, 2022 at 10:03
  • 1
    I think what @GdD is trying to say is, if you are missing coolant, it's going somewhere. There are four places (to my thinking) it could be going. 1) Leaking onto the ground; 2) Boil over; 3) Out through the combustion chamber due to a head gasket leak; 4) Into the oil due to an internal leak ... or a combination of any of the above. Considering you state there is a lot of pressure when you release the radiator cap, it seems to me you might have a head gasket leak. You should have the cooling system checked for combustion gases, as they would not be there normally. Commented May 19, 2022 at 10:36

1 Answer 1


I'm going to assume that you mean your coolant is disappearing and you keep having to fill it up. In cases where there is coolant loss, you need to determine WHERE it's going.

The usual places are:

  1. Leaking out into the world. Usually there are signs of this with coolant seeping or squirting out under pressure when the engine is hot. Check the radiator, coolant lines and hoses, the engine compartment (top and bottom), the pressure cap and the coolant reservoir, and the lines to the heater core. There should be a sticky residue in any area where it's been leaking out.

  2. Leaking into the engine oil. Check your oil for signs of coolant. Often the oil will smell like coolant and you'll have "froth" that looks like what you get with cappuccino only darker. An oil analysis test will show coolant in the oil.

  3. Leaking into your combustion chamber. Here the coolant can literally go up in smoke as it's burned in the engine. But any shop with an Exhaust Gas Analyzer can determine if there is coolant in the exhaust or not. Sometimes you can smell it, other times not.

Once you have determined where the coolant is going, then a plan to address it can be formed. But unless the problem is external to the engine (i.e. radiator, lines, etc.) the fix will almost certainly involve engine repair.

I'd be suspicious of both mechanics since neither of their stories make any sense, at least not the way you have repeated what they said.

  • Thanks a lot for the info. I will try to detect/debug the issue and will let you know if needed. Again thanks, the info, you provided me, certainly, its useful for me
    – Phoenix404
    Commented May 19, 2022 at 11:37

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