Mad Motors Blog

10 Responses to “What is the problem with filling your engine coolant above the max level?”

1. 

   emma_jean2
   

   08. Feb, 2012

   less room for evaporation will lead to excessive pressure in the system which stands the chance of blowing a gasket!
2. 

   jimbob
   

   08. Feb, 2012

   it will cause too much pressure and blow your head gasket
3. 

   harry
   

   08. Feb, 2012

   the water needs a litttle room to expand when warm
4. 

   WHO am i?
   

   08. Feb, 2012

   the hot coolant wont be able to expand and blow out the overflow or blow head gasket
5. 

   thastoneroses
   

   08. Feb, 2012

   well it says dont do it so dont. if i told you not to shoot yourself would you do it?
6. 

   John S
   

   08. Feb, 2012

   It can get your engine wet. And when the antifreeze evaporates, it smells.

   Other than that, yer good.

   Liquids expand when the get hot, and the cooling system is a sealed system. This means that the coolant CANNOT expand, because there’s no place for the excess to go. But, the radiator cap has a pressure release built into it, so that when the pressure gets too high, *SOME* liquid is permitted to flow out of the coolant system into a resevoir. Now, if you have already filled that resevoir to the top, the additional hot liquid from the radiator will cause the resevoir to overflow.

   Getting your engine wet, and smelling up the car temporarily. And no, it will NOT blow out your head gasket. Guarantee.

   No big deal.

   Unlike overfilling your oil or transmission. Now THAT is BAD.
7. 

   scullion.foredo
   

   08. Feb, 2012

   You have overfilled the reservoir, right? If so, don’t worry. You won’t blow anything . . . no head gaskets . . . . nothing. The reservoir is not pressurised. It vents to the atmosphere so it will not burst or anything.
   The level mark is just an indicator of a safe level to fill it to avoid any spillage of hot coolant (it will only happen when it’s hot).
   What usually happens is that, when your engine gets hot and the coolant expands, a pressure valve lets the excess coolant out and into the reservoir. When the engine gets cool, the coolant contracts and the pressure valve allows coolant to be sucked back in from the reservoir. See? No big deal.
   Suppose you have overfilled the reservoir and suppose your engine gets hot . . . coolant goes into the reservoir. But what if there is not enough room for it????? It overflows a little bit onto the road. See? Nothing to worry about.
8. 

   nosdda
   

   08. Feb, 2012

   ,The Max mark is there to allow for expansion. As your water heats up, It expands. That is what causes a saucepan of water to boil over. So if there isn’t enough room left to allow your rad water to expand it will find its way out somewhere else, and can possibly damage your radiator.
9. 

   swenson0
   

   08. Feb, 2012

   Nothing
10. 

    fred405
    

    08. Feb, 2012

    OK most answers here are wrong

    Effectively over filling will cause no damage whatsoever providing your system is working correctly in the first place

    The pressure cap on the radiatpr or header tank is designed to release at a given pressure and this it does in order to allow for expansion. On cooling another valve allows air to replace the contracting coolant.

    If during the expansion process there is in fact too much coolant it WILL escape through the pressure cap and discharge on to the road, normally through a small hose that takes it to a safe place under the bonnet

    So do not worry too much