My 1977 MGB overheats why?

Question

I picked it up 2 days ago. On 2 out of 4 journeys the temp., gauge has gone over to the red. does this mean the thermostat is dodgy?

Answer 1

usual reasons for overheating are:-
.. in particular order

low water in the cooling system /leaks in the cooling system
defective stat
water pump failing
fan belt not set correctly
coolant system pipes are partially blocked meaning inadequate cooling

solutions
check the level, top up if required, check the level after a journey if its droped then you have a leak.
check the sta is workign by following the workshop approved technique (remove the stat from the system (WHEN COLD), place in a pan of water and brogn to the boil.. if the stat changes size then its working.
check the amount of slack int he fan belt.... if its too slack it may be slipping on the fan belt....
look for obvious signs of leaks or staining on the pipework and engine

after that Id guess you are probably looking at professional help. you could try reverse flushing the rad (fin which way the water runs through the rad and then disconnect the pipes and run water form a hosepipe through the opposite way, that can flush out built up crud.

Answer 2

Some of the old engines "silt up". Means that the rust that forms on the insides of the water passages in the block settles down in the cavities of the block like sludge and keep the system from cooling properly. That, by the way, is pretty exotic, but with a car this old it is possible. And, yes, sometimes the thermostats go bad. And sometimes you can get a different temperature range when you replace it. Or maybe you need to have the radiator "rodded" where they disassemble it and force rods down the core to ram out the accumulated junk. Or, maybe you can have the block boiled if you do an engine rebuild. Start with the cheap chemical cooling system cleaner you can get at the auto parts house. It probably won't do any good, but at least you will have tried. Welcome to the brotherhood of British Car owners! Be thankful you don't have an MGA.

Answer 3

most thermostats fail "open" so its not liley to be that. The radiator and block will probably need a good flush with a hosepipe. there is a drain plug on the radiator and a tap on the block. There will a be a lot of crap coming out!. Try to reverse flush, put the hose pipe on the bottom of the tap on the block and blow water through.

When you have finished there may be air blocks, run the engine with the water reservoir cap off and allow to tick over for 10-15 minutes watching the air bubble through

Answer 4

It could be the thermostat or the temp sender unit - available from good spares shops like Premier Supply Autoparts

Answer 5

Could be the thermostat, a leaking pipe, a leaking radiator, over revving for some reason, carburation problems making the engine work too hard..........

Answer 6

MGB is very common to overheat go to www.mgownersclub.co.uk am sure they have info for ya

Answer 7

my brother had a calibra, it had the same problem, once we were on the moterway and it was reaching the red when the fan kicked in and quickly cooled it!

check the radiator aswell, and that theres enough water in there, and that it's not blocked with dirt!

Answer 8

Hi

As long as the car is running okay and you're not losing any coolant (sleep-yes, coolant-no!) then the first thing I would do is change the thermostat.

Best of luck

Geordie

Answer 9

ooh ooh I know... It's old 'n' busted!
Er... dodgy rather... right then carry on.

Answer 10

did you check coolant?