Thread: TD5 coolant leak at fuel cooler

Originally Posted by NWTASD2

Hi,,

I have the same issue as Designosaur.

So are my hoses supposed to be HARD or SOFT after a run.

When its at operating temp.

Cheers.

How do I check operating PSI/KPA?

How do I check if I have a faulty radiator cap/expansion tank.

Cheers

If everything is working properly the radiator hoses should be hard when the engine is up to temp.

When the engine is 'cold' there is no pressure in the cooling system and the radiator hoses are soft. As the coolant temperature increases it expands creating pressure in the cooling system which makes the hoses feel hard. The amount of pressure build up in the cooling system is controlled by the radiator cap which has a relief valve which opens at a pre determined pressure and releases coolant into the overflow tank or reservoir causing its level to rise. This is why the overflow tank should not be filled to the top when the engine is cold as this leaves nowhere for the expanded coolant to go. Pressurising the coolant increases its boiling point which allows it to work more effectively at higher temperatures. The engines thermostat regulates the coolant temperature to a pre determined temperature. The radiator dissipates excess heat.

When the engine is turned off the coolant temperature decreases. This causes the coolant to contract creating negative pressure in the cooling system which then sucks back the coolant from the overflow tank into the cooling system. When the engine is cooled down its radiator should be full as the level in the overflow tank decreases to its original level.

All very fine in theory but leaks in the system allow coolant loss as the pressurised system pumps coolant out. Worse still when the engine cools air is sucked into the system instead of coolant from the overflow bottle resulting in even lower coolant level in the engine. The problem (lack of coolant) compounds each time the engine is run up to temp and allowed to cool down. Even a very small leak that may be losing a seemingly insignificant amount of coolant is enough to result in overheating. A symptom of this problem is that the radiator level is low but the overflow bottle coolant level is at its high or hot mark.

Radiator/coolant system pressure caps come in various shapes and sizes and whilst your local radiator man will have the gear to test them its better to "when in doubt toss it out". Avoid after market replacements go for OEM or original, its cheaper and less painful in the long run.

If the radiator hoses don't go hard when the engine is run up to temperature you have either a major leak or a crook pressure cap


Deano

From RAVE, Bob

Expansion tank [TD5]

The expansion tank is located in the engine compartment . The tank is made from moulded plastic & attached to brackets on the right hand inner wing. A maximum coolant when cold level is moulded onto the tank.

Excess coolant created by heat expansion is returned to the expansion tank from the radiator bleed pipe [ goes from the small spigot on the top of the radiator on the passenger side, to the small spigot on top of the expansion tank] An outlet pipe is connected into the coolant pump feed hose & replaces the coolant displaced by heat expansion into the system when the engine is cool [ connected to the expansion tank underneath , joins the coolant from the fuel cooler thermostat outflow, connects to a small pipe which connects to the larger Water pump inlet pipe.]

The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve, which opens to allow excessive pressure & coolant to vent through the overflow pipe [ to atmosphere, in the engine bay, the small hose next to the radiator bleed pipe at the top of the expansion tank. ]The relief valve is open at a pressure of 1.4 Bar, 20 psi & above.
For a TD5 engine.

For what it is worth I think if the coolant system was being pressurised by head gasket problems, the excess pressure would be obvious, & manifest itself at the worst case, by excessive evacuation of the coolant from the expansion tank into the engine bay. My opinion is there will always be a small amount of pressure in the system[ below 20 psi ] if the system is leak free, & not worth getting worried about. I was told one check is to take the cap off, & check to see if air is being delivered from the radiator bleed pipe , which could indicate head problems. However, I am not an expert, & welcome any input , Bob