Overheating

Hi, all,

Hoping someone might be able to advise me on a problem.
A few times when I was off-roading I noticed that my water temp guage had gone into the red. When this happened, I stopped the car immediately and left it for for 10/15 minutes and the temp went back to normal and then stayed normal. This only happened about 3 times over the course of several months. Generally the temp guage would sat a little under half-way. I never had steam coming out of the radiator, and coolant seemed to remain on max.

Now, this week the car started overheating on the motorway, and I stopped the car and found that the coolant bottle was empty and I could see some coolant was leaking (visible at the bottom of the radiator). 

I am obviously going to replace the radiator, but I am wondering whether I have an additional problem? Obviously, the car will overheat with the leaking radiator, but I don't know why I was getting these "sporadic" occastions when it was overheating before, and then seeming ok for weeks or months? Would this just be radiator getting blocked up as it deteriorated, or might there be a problem with some valve or sensor that controls the water flow or something? (sorry, I am not very mechanical, so don't know how the cooling system works).

Any advice very much appreciated.
Cheers,
Lee
 

Thanks for the info, Lambert. Would there not be other symptoms if it was the head gasket, like white smoke from the exhaust or something?

I would follow Lamberts advice. The coolant is probably being forced out of the hose joins of the cooling system ,as it is getting pressurized from the gasket being failed. This also air locks the system so water will not be circulating. One way to determine is wait for the engine to cool fully and then open the radiator cap. If it hisses you know that air is being forced in on the compression stroke on the engine. I had the same issue for ages and it just gets worse. 

you get a push and pull action on the oil and water. Intake stroke (sucking) will draw oil and water into the combustion stroke producing blue/white smoke. combustion stroke (push) will force exhaust gas into the oil and cooling system.

Thanks for the info. I will try this test with radiator cap tomorrow.
So, if there is no hiss then there is no reason to think a head gasket problem?

It's all been said, it's possible it's a head gasket  leak to a cylinder.
You could also take the plugs out, they should all look the same colour etc. An overly different one (usually cleaner) is the cylinder into which the coolant may be heading. Another indicator is momentarily running on 3 cylinders for a few seconds first start of the day, but usually ok after this for the rest.
Just some things that may help.
 

I did the test of getting the car up to temp and then letting it cool a bit and opening the radiator cap. There was no hissing sound, so I assume that indicates there is no issue with the head gasket (necessarily)?

Also, no smoke from the exhaust. Oil looks normal on the dipstick. No evidence of oil in the coolant

sounds promising, perhaps it was a coolant leak. If you find it overheating and you cant stop, put the cabin heater on full and blower on full. You can dump a huge amount of heat that way and the temperature should reduce quickly.

The only real way to check is to pressure test the cooling system. It's not a complex process, in simply terms replace the radiator cap with a bung and use a pump to pressurise the system to a few PSI, wait a few hours and check the pressure is the same. If it's not you have a leak and need to find it.
You can make something (see YouTube) or purchase a tester for about £50, or get a garage to a test for you. 

You say you have a leak from the bottom of the radiator, it's possible it's the radiator or top hose, both will drip randomly from the radiator bottom, so check the source of the leak or just replace both.

Even after this a pressure test is the only conclusive way of checking for leaks and that no other issues are present across the complete system.