1275 overheating

Post by **jameswallace** » Sat Apr 26, 2008 8:00 pm

I fitted a 1275 MG Midget engine to my convertible moggy back in the autumn of 2007. I got the engine off of ebay and the guy who sold it did't know much about it other than it was running sweetly when he saw it in the Midget he took the engine out of. When I fitted it it ran nicely with no smoke coming out the back, and it pulls really well, so I think it's generally ok. It's got an LCB branch manifold and a big bore exhaust. We drove it on a long trip over the christmas period and must have covered over a thousand miles all together - running ok, but always very hot - 90celsius cruising at 65 mph - go above that and the car would boil. I thought this overheating might be to do with a blown head gasket so I replaced that today ...... but it's still doing the same thing. It's been so hot that it's sprung a leak in the radiator. So, my question is, what else could be causing the overheating - a knackered rad ? - it looked ok until it sprung a leak but might br original as it's beginning to lose the fine fillaments between the pipes.

Post by **d_harris** » Sat Apr 26, 2008 8:05 pm

My initial reaction was to check the rad, get it out of the car and give it a good flush through. The minor cooling system is more than sufficient for the 1275...

The other thing to do is get all the rubber pipes off and check they aren't clogged up (not likely, but for the sake of a few minutes, worth checking)

Post by **Packedup** » Sat Apr 26, 2008 8:08 pm

Is 90c really running hot? They run a pressurised cooling system, and you may well have an 88c thermostat in there - So I wouldn't call 90c hot, more like normal!

If the rad is springing leaks then it's pretty tired - The cap should lift on its spring and let coolant out the overflow long before a core should let go.

Start with the basics when it comes to keeping the temps in check (if they need to be - What do you mean by "boil"?), mixture and timing. If they're OK then check the stat is opening fully, replace the water pump (by the time you've removed it to check you might as well fit a new one), look for bubbles in the radiator with the engine running (head gasket/ cracking between cylinders and water jacket), make sure the hoses haven't collapsed, etc.

One thing to double check is that the fan is on the right way round - If not, the faster the engine goes the more it's going to fight the incoming air through the radiator!

Post by **jameswallace** » Sat Apr 26, 2008 8:15 pm

Dear "Packedup" - Is it possible to see a crack between the cylinders and the water jacket with the head off ?

Post by **mrbenn** » Sat Apr 26, 2008 8:47 pm

Have you got the correct pressure rated radiator cap?

Post by **Packedup** » Sat Apr 26, 2008 9:03 pm

Maybe - I've only ever seen a crack in a head, and that was an alloy head with a very tiny crack, only visible because it has steam cleand the combustion chamber over time!

Signs of coolant into the cylinders or combustion gases into the cooling system would be easier to look for. A very clean and shiny spark plug would suggest that cylinder is getting coolant in it, bubbles and exhausty smells in the radiator would suggest gases being forced into the cooling system.

Or if it's really bad, taking the plugs out first start of the day and turning it over to be greeted with a fountain would be pretty conclusive!

Post by **Matt** » Sat Apr 26, 2008 9:08 pm

Im with Dan, Blocked radiator/hoses.

This may seem counter intuitive, but does it definately have a thermostat? If not it needs one or a blanking sleeve! The restriction causes turbulance in the water flow and make sure the temp is evenly distributed and you are less likely to get hot spots

Post by **jameswallace** » Sun Apr 27, 2008 9:12 am

Dear all, thanks for all your input - I don't have a thermostat in there at the moment but will get one, will change the rad for a new one, and will look into the cracked head (not mine) side of things. I think the timing's ok but worth checking I guess. As for the hoses, they seem good, and the fan is the plastic one that came with the original engine which only fits one way round.

Jim

Post by **IslipMinor** » Sun Apr 27, 2008 9:58 am

the fan is the plastic one that came with the original engine which only fits one way round

What fan have you got? I don't think the Midget one will fit in the space in a Minor, but a Mini will - the only problem is that it is a 'pusher' fan!! The faster you go the less air it allows through in a Minor! Turning it round makes no difference - it's still a pusher fan, though slightly less efficient!!

Before doing anything major, I would do 5 things:

Check/adjust the timing - very retarded will overheat.

Check/adust the mixture - weak will overheat.

Fit a thermostat (82° or 88°) or the proper BMC blanking sleeve, as no thermostat can cause overheating through the circulation being able to 'short circuit'.

Make sure that the heater is connected - flow and return - and the valve left fully open. This allows a good circulation of water through the back of the engine - more powerful A-Series can overheat cyls 3 & 4 if not.

Remove the fan completely for test purposes (unless you live in the centre of a large town and likely to get caught in heavy, slow-moving traffic?), or use a standard Minor 2-bladed one.

As has been said previously, the Minor has a good capacity standard cooling system, and should be perfectly ok with a 1275 engine. On our 1380 I have fitted a higher duty radiator and water pump, 82°C stat, 10 psi cap, no engine fan and a 9" electric fan in front of the radiator on a thermo switch - all works very well.

As a note the 9" SPAL electic fan is thinner than most others and fits in front of the radiator with no mods at all. It keeps the temperature at around 90°C in stationary traffic; went up to about 95°C on the M25 near Heathrow when the temperature hit 100°F for the first official time a few years ago - more than can be said for many modern cars, the hard shoulder was littered with them!

Post by **Matt** » Sun Apr 27, 2008 10:32 am

You dont need the proper BMC blanking sleeve, removing the middle from a standard 'stat will have the same effect

Post by **bmcecosse** » Sun Apr 27, 2008 11:04 am

I'm not so sure that's true Matt - the shape is entirely different - and when a stat opens it only opens a ring around the ecntre for water to flow through. But blanking sleeve is for competition engines only - on a road car a thermostat is the way to go. I suggest fitting a lowly 74 stat for summer use - and if using a Minor single balde fan - get another and fit it at right angles. As siad already - turning a fan round doesn't make it blow the other way!! But a Mini fan is useless. Double Minor fan should be plenty. Block cracks are 'almost' unknown unless the engine has been bloiled dry at some point ? Head crack is possible - but not common - and should be easily enough seen on the clean surface. You can also try flushing the cooling system out with drain cleaner (or rad flush) - and a new radiator will be a good idea - or have that one re-cored at a specialist. may be worth inspecting the water pump for any damage to the impeller - and is it the later 'big' impeller in there ? Also - is the water pump pulley a small diameter - or has a larger pulley (ex Mini) been fitted ? The larger pulley cuts down the pump and fan speed and can cause heating problems - small pulley is better!