How to Tell If a Radiator Cap is Bad and Replace It

By | January 27, 2018

How to Tell If a Radiator Cap is Bad and Replace It
Radiator caps can go bad and need replacing which is an easy task most anyone can do.
Remember never to remove a radiator cap while the engine is hot as the cap likely is under pressure and boiling water can spray out.
Only remove the cap when the engine is cold.

What is the Function of a Radiator Cap?
The basic purpose of the cap is to give a pressure outlet when an engine becomes hot and overheats.
It does this with a spring loaded plunger that has a set pressure point to give way.
When the pressure is released water will spill out into the reserve or from the cap itself.
Bad Radiator Cap Symptoms
As a cap ages the spring that controls the pressure can release early letting fluid spill out.
This can leave a vehicle low on fluid and lead to overheating which in turn make the cap leak out more.
Air also is let into the system which passes air bubbles into the cooling system. Since air is not good at transferring heat quickly a motor can overheat more easily when air bubbles are in the system.
Symptoms can include overheating, burnt stains around the cap, and loss of fluid.
Here white spots around cap show where fluid has been leaking out.
Radiator Cap is Bad
This radiator cap is rusted and needs replaced.
Radiator Cap is Bad rusted
Replacing a Bad Radiator Cap
1… The first step is to buy a new radiator cap from an auto part store or online.
Example Radiator Cap On Amazon
Stant 10231 Radiator Cap – 16 PSI Vented

2… Be sure the engine has cooled down and the cap is no longer under pressure.
3… Remove the cap by pressing it down and turning it counter-clockwise.
Replacing a Bad Radiator Cap Turn to Left
4… Match the old cap to the new cap making sure they are the same.
Replacing a Bad Radiator Cap
5… Put the new cap on by matching the notches, pressing down and turning it clock-wise.
Replacing a Bad Radiator Cap Turn to right



2 thoughts on “How to Tell If a Radiator Cap is Bad and Replace It

  1. Tom

    Was losing radiator fluid but no fluid was on my driveway. I changed the radiator cap after watching your video and the problem was solved. I did find the white residue you were talking about near the radiator cap.

  2. doug

    Awesome job maybe mention rubber deteriorates so quickly now days causing problems


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