[LFY]

Hi everyone,

My upper radiator hose gets firm when the engine reaches operating temperature. It is firm but not hard. It is still squeezable to some extent (about 4 to 5 centimeters).

I am worried about this. Does my cooling system have higher than normal pressure?

Also worth mentioning:

1 - My car doesn't lose any coolant
2 - The temperate gauge is always within normal range
3 - No overheating issues
4 - No air in the system
5 - Engine runs fine and pulls nicely
6 - Thermostat runs fine
7 - No oil in coolant or coolant in oil
8 - No bubbles in coolant at the radiator filler neck whether the engine is cold or hot
9 - Radiator cap was replaced 2 years ago

The engine is XU7JP4 LFY.

So, why my upper radiator hose is not soft to the touch? Is my headgasket blown? Should I tear the engine apart?

 

[noddy-hol]

HI...to me no1 to no9 means all is well...dont look for problems....the coolant systerm will be under pressure anyway when its at the right temp

 

[LFY]

I should also say that the hose was soft to the touch before i replace radiator cap. After replacing it got firm.

Does it mean that the faulty cap didn't allow the pressure to build up in the system?

 

[noddy-hol]

if it was the correct cap then all should be ok...what was wrong with the old one?

 

[LFY]

if it was the correct cap then all should be ok...what was wrong with the old one?

Yes, it is the correct pressure (1.4 bar)

The old one hadn't been replaced for 10 years! That's why i replaced it.

 

[noddy-hol]

ah....so 1.4 bar means about 20 psi pressure max in the cooling system...like a semi flat tyre....so all is good

 

[LFY]

ah....so 1.4 bar means about 20 psi pressure max in the cooling system...like a semi flat tyre....so all is good

This is my cap:
PEUGEOT 405 93-97 EXPANSION/RADIATOR CAP OE QUALITY | eBay

If you think that's a lot of pressure, I'll replace it with a lower pressure rating such as 13 or 14 PSi.

 

[WillNZ]

1.4 bar is correct for your car, dont replace it with one with less pressure. At 1.4 bar the hose will feel hard so all ok..:thumb:

 

[LFY]

1.4 bar is correct for your car, dont replace it with one with less pressure. At 1.4 bar the hose will feel hard so all ok..:thumb:

You are right. But there is something I don't understand. Why Peugeot has chosen such a high pressure radiator cap for a normal passenger car?

Peugeot 406 1.8 is not a high performance car like a Ferrari or Porsche!

Most cars use around 13 PSi pressure caps. Even a 10 PSi pressure cap can still increase boiling point to the extent higher than needed in a passenger car.

1.4 bar = 20.3 PSi! That's extremely high for a 406 1.8!

The boiling point of my car's coolant = 110 °C

Can someone please explain the reason behind using a high pressure cap for a city car like 406?

 

[noddy-hol]

Hi...I hope you find the answer to the cap pressure,but if your car was designed with it...and it runs ok...what are you trying to achieve?I would class the 406 as a motorway mile muncher not a city car but does both well...enjoy your car...