Upper radiator hose is firm

[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?

[xantia_v6]

The vapour pressure of the water at 80 degrees is about 45 kPa (about half an atmosphere), so it is normal to feel some pressure in the hoses. See the table in the right hand side of the page at: https://en.wikipedia.org/wiki/Vapour_pressure_of_water

Note that in general, the applicable temperature for calculating vapour pressure is the highest temperature that the water is exposed to in the engine, not the average temperature.

[white exec]

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.

Mine does exactly the same. There is nothing to worry about. You can cancel that appointment with the Doctor...

Sorry, couldn't resist!

[elma]

Agreed, totally normal.
When the engines cold the hose is soft because the thermostat is closed and the hose is out of circuit.
When hot the thermostat is open and the hose is pressurised.

[LFY]

Thanks for your answers.

But i have a question:

If that's normal, why is it said that firm radiator hose is a sign of blown headgasket resulting from combustion gases entering cooling system?

[elma]

I think solid rather than firm would be a better word to use in that situation.
More likely that the coolants going to jump out of the bottle really before you notice a hard hose if the heads leaking.
From the description you gave in the first post it doesn't sound like the HG is gone on your engine.

[CitroJim]

My Activa runs a very firm top hose... Always has and I'm speaking 8 years here...

Again, panic ye not. You have no problems at all... HG is definitely not on the way out...

[LFY]

So, a blown headgasket makes the hose ROCK HARD rather than firm and compressible?

Let me say this:

Some days ago when the engine was hot and running, I waited for the cooling fans to turn off. When they turned off and the temperature was about 88 °C, I tried to open radiator cap to see what happens! I knew it is dangerous but I took safety measures (gloves, eye protection, etc). When I opened the cap no coolant rushed out of the system and it didn't seem that the system had excessive pressure. The coolant level was full too. If the HG was blown the coolant should rush out of the system violently at that temperature, right?

I also tested something else. I turned off the engine and waited for about 2 to 3 hours for it to cool down. I then opened radiator cap and didn't hear a big hissing noise. I have heard that if an engine's HG is blown, when you open it's radiator cap after some hours you can hear a popping noise like opening soda bottle. But my car didn't have that noise.

[elma]

Head gaskets can go in several ways. They have veins for oil and coolant within. Then on the inside you've the combustion gases. On the outside the air around the engine.
They can leak between any of the four things and each way has its own symptoms. A leak between the combustion gases and the coolant will pressurise the coolant but before you notice a hard hose the valve on the coolant bottle will release coolant (19psi I think is the blow off pressure) unless you are very quick in noticing the temp gauge rising above normal or that the power is down on the engine.

If you're not down on power, have no milky toothpaste type stuff in the oil or signs of oil in the coolant and it's not spat the coolant out theres no need to be looking for a HG problem.

Taking off the coolant cap with a hot engine is a bit of a bad idea. No amount of gloves and goggles will protect you from the amount of steam that can come out and it can go a long way. The coolant can be over 100degrees even in a healthy car and if it was you would have probably been very badly burned as releasing the pressure will turn it to steam and froth that erupts from the bottle like a volcano. Please don't do that again, as a test it achieves almost nothing anyway.

If you really must have the head tested buy a gauge to test the compression and buy a pump to pressure check the cooling system. Personally I don't think you need to unless theres something you've not mentioned that has led you down this path. The tests you are doing are misinformed, dangerous and not giving you any actual information.

[LFY]

buy a gauge to test the compression

I also checked engine compression in all cylinders and the results was:

210 - 209 - 209 - 210 (PSi)

Personally I don't think you need to unless theres something you've not mentioned that has led you down this path.

These forum topics led me down this path:

http://www.team-integra.net/forum/11-ge ... -hard.html

http://www.allfordmustangs.com/forums/c ... nning.html

http://www.toyotanation.com/forum/103-c ... -4cyl.html

http://www.dsmtuners.com/threads/upper- ... re.364247/

[white exec]

All modern cooling systems run "pressurised". The expansion cap is the 'safety valve', and usually designed to relieve pressure at about 1.3bar (20psi). The reason for this is that water (coolant) in most car cooling system has to operate between 85 and 90degC, and may therefore go towards the normal boiling point of 100C when working really hard. By upping the pressure, the boiling point of the water (coolant) can be increased, allowing non-boiling running up to 130C. (Boiling must be prevented, as it generates steam - which expels water and produces damaging hot-spots - and can form unwanted deposits, if not de-mineralised.)

When the engine heats up, the coolant expands, and pressure is created (volume and vapour), which makes the hoses feel firm/solid. As it cools, the hoses relax, and the pressure cap is designed to 'inward vent' to prevent a vacuum forming.

If you're not losing water/coolant, and the level remains stable in the expansion tank, everything is ok.

[elma]

These forum topics led me down this path:

But not something you noticed on the car?

Those pressures you got are so closely matched I'd be very happy with them.

[LFY]

I know the basics of cooling system operation and the rules behind it. I was just curious about the firmness of the hose.

[LFY]

But not something you noticed on the car?

What should i notice on my car?

[elma]

Loss of power, overheating, toothpaste in the oil, misfiring.......