Overheating Sprint

[IFM]

At the weekend I took my Sprint out for a short drive. After about 5 miles I noticed the temperature gauge was 100 degrees. It normally runs between 80 and 90 on a hot day.

I immediately switched on my electric fan (I have a dashboard switch for it as well as an Otter switch on the rad) and the heater. But the temperature was rising fast... Luckily there was a handily placed pub car park so I pulled in. By the time I'd stopped and killed the engine the gauge was at 110 and still rising.

A quick peek under the bonnet revealed the radiator was stone cold, as was the pipe from the engine. I checked the gauge again and it now showed 115 (the maximum) and I could hear a quiet hiss coming from the radiator cap.

A couple of minutes later the pipe from the engine started to warm up and the hissing stopped. I deduced that the thermostatic valve had probably stuck initially but had just opened. So I started her up and blipped the throtle to see if the circulation of water through the radiator cooled it down, which it did pretty quickly. I thought I'd take her straight home and she ran at about 90 (it was fairly warm) all the way back.

Am I right in concluding that the thermostatic valve is the culprit. Is there anything else i should consider?

Car is running twin Webers with Shell V-Power petrol (plus Castrol Valvemaster lead and octane boost).

Any help offered would be great....

[Emma-Knight]

I think you are right - jammed thermostatic valve - maybe some rust or chalk particle in the cooling system got stuck there. ( I flushed my cars cooling system and got a lot of small particles out of it, the heater was almost completely blocked but freed by flushing it backwards) It would be good to change the thermostat valve - its a cheap component - and maybe to flush the system, and take some fresh coolwater (not from Davidoff) - antifreeze and water.
I would not suspect the waterpump as the top tube to the radiator would not have been cold then. Anyway - the paddles wouldn't rust out over night...

Anna

[RotoFlexible]

When starting out, I always keep one eye on the temp. gauge esp. if I haven't driven the car for a while. Typically, it goes up into the 80's or perhaps to 90, then the thermostat snaps open and the temperature plummets as the cold water from the radiator mixes in. It then works its way back up to running temperature. After this has occurred, the temperature stays pretty stable. If it starts making runs into the higher numbers, it usually means that the coolant level is low. I had a steady slow leak from a partially rotted freeze plug. The engine rebuild currently under way will take care of that.

[gordonlund]

A common cause of thermostats sticking is "furring" up of the water system by using hard water (Calcium and lime deposits as in a hot water kettle) If your kettle has a white coating on the inside do not put the same water in the car. Use de-ionised water or if you are feeling rich use distilled water. Or better still, take a ride to a soft water area and fill up a large container for future use. In the Northwest of England, most of our tap water comes of the fells which if anything is slightly acidic coming off peat bogs, not alkaline that comes out of chalk beds.

Before refilling your water system, if it is showing signs of calcium deposits, try and remove it with a flushing agent.

When I first stripped my Spint engine, it was coked up with calcium / lime deposits and would have been a complete nightmare. I had to scrape it all out particulary from the water pump components, (all the service bits got slung), and the thermostat housing. I through the stat away as I did the radiator core which was replaced with a modern 3 core between the existing lower and upper head tanks and a new stat installed.

I have always run my Twinks on 50% Bluecol antifreeze which keeps everything shipshape, corrosion and deposit buildup free, increases the boiling point and decreases the freezing point of the water.

Best regards

Gordon Lund

[freddy22112211]

I threw my thermostat away years ago!
Gordon

[1964 S1]

Sounds like the thermostat to me.

ps; I've got 12 and 10 year old coolant fluids in my two Lotuses, I've never flushed them since I bought them. All the talk about types of water and replacement flushes baffle the three of us.

[hatman]

Sounds like the thermostat to me.

ps; I've got 12 and 10 year old coolant fluids in my two Lotuses, I've never flushed them since I bought them. All the talk about types of water and replacement flushes baffle the three of us.

It has been my understanding that the anti-corrosion inhibitors in the antifreeze lose their effectiveness after a couple of years, leaving the engine open to internal corrosion and possible blockage of the waterways. Or maybe it's just an industry con to get us all to keep buying new antifreeze. Any experts out there?

[IFM]

Thanks everyone. There's plenty of coolant in there and it was fresh about six months ago. I do live in a hard water area but am not sure whether any tap water was added to the coolant (as I didn't do it myself).

Sounds like my diagnosis of a dodgy thermostat was probably right...