Pressure in 1.6 NA cooling system

[overdrivegear]

The upper radiator hose has a ton of pressure on it.  I pulled out the thermostat to see if it works and everything checked out there.  Even up at operating temperature, the fans never kicked on and the upper hose stayed highly inflated, so I assume the thermostat never opened.

Is this a common type thing?  I know the cooling system is supposed to have about 16 psi on it but I'm afraid of something else going on that will burst hoses.

[rov716y]

if you take of you  filler cap you'll find white smoke in there telling you the head gasket is failing.  my 1.6 n/a does the same

[Vincent Waldon]

If your t-stat is opening the lower rad hose will get hot... if the hose is cold the t-stat hasn't opened.  It can take quite a while to open, particularly on a diesel idling in a garage, since diesels produce so little heat at idle.


Probably a good idea to differentiate between pressure when the system is hot, and pressure when the system is cold.

When hot, the system is designed to operate in the 15 psi range.. that's enough to really pump up the heater hoses (particularly the upper one).  The cap will release if the pressure becomes extreme... can't remember off-hand the exact value.  In any event,  operating temperature and pressure will mean that the upper rad hose is hard to squish.... 15psi inside a large hose like that is a fair amount of resistance.

Cold, the system should have *no* pressure.  If it does, that's a common sign of a head gasket leak.  The usual test is:

1) with the engine stone cold, open the rad cap to release any residual pressure
2) tighten the rad cap
3) start the engine and run it for 1-2 minutes only
4) shut the engine off
5) open the rad cap and listen carefully.... a "whoosh" of air escaping suggests the system is pressurizing itself... often the sign of a head gasket problem.

[Ziptar]

You can also try this:

With the engine cold remove cap.
Make sure reservoir is full.
Start Engine.
Wait to see if you get intermittent geysers that blow out of reservoir.
There will be constant run off as it heats up because water expands but, if there are large spurts, head gasket is bad.

Don't stand too close while you do this... :wink: