Heat sensor or thermostat problem after 1.7 rad hose burst.

[Welsh Dave]

My R-reg 1.7 Puma's top hose exploded at the engine end. At first I thought the loud bang was from hitting a pothole, but it was soon evident from the soaring temperature and a whirring rattle that there was a problem. The hose is in shreds over about three inches.

I got the car home by topping the header tank up wherever I could get water (lake, canal, tap), and the dashboard temperature gauge was working perfectly at first, but as time went on it went off the scale, which it now does immediately whenever I switch on, irrespective of engine temperature. The sensor is presumably stuck or broken.

Today I replaced the hose, and used it, connected at the engine end, to fill the engine with coolant. I then connected the radiator end and filled the header tank, expecting the rad to fill. The engine idled normally for about 10 minutes, during which the rad stayed cool and the level in the tank didn't change. I now suspected a sticking thermostat, but after a 10-minute rest the rad was full and the tank level had dropped. Topped up, the engine then idled, again smoothly and without signs of overheating, for at least 15 minutes, but the radiator did not heat up. I'd have expected the fan to start by then.

I suspect interconnected problems in the Puma's complex systems. Any ideas?

 

[748]

For a cooling hose to burst like that, there must have been excessive pressure in the cooling system.
Pressure is held in the system by the expansion tank cap, this increases the boiling temperature of the coolant.
The cap is not simply a cap, it has a relief valve built into it. Perhaps it's blocked?
Have a look at this diagram, it may help you understand the coolant flow.

 

[Welsh Dave]

Thanks, 748. I replaced the cap too, just in case, so it doesn't appear to have any bearing on the current situation.

 

[Welsh Dave]

I had a problem getting the grey connector off the engine coolant sensor, but it's solved now.