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MG MGB Technical - Running hot.... even in the UK!

The story so far:

I bought the MGB (1964 & 56,000 miles) ages and ages ago. I was for rebuild, and never ran it.

When I rebuilt it I found that the previous owner had stopped the water pump leaking with Radweld. The heater was blocked with it, the water was orange, so it was everywhere. I was told that the three bearing engine water pump was briefly unavailable so that might account for his stupidity. It had almost knackered the bearings.

I cleared the heater (off the car) with bicarbonate of soda, it took two days.

When rebuilding I changed all of the hoses.

After running for a few years without ovwerheting problems I put a different 18G block on the car, all balanced and very nice.

Much later I swapped the radiator.

When I swapped to unleaded petrol and an unleaded cyliner head it seemed to start running hot.

After a long run if I stop it it is impossible to start until it cools (possibly due to fuel vapourisation?).

Unfortuately the heater tap had keaked all over the distributor and I couldn't shift it.

Now I have had the distributor replaced with a more modern one and had the ignition checked out by an expert, but if anything it runs hotter. Last weekend at 23 degrees C (what's that 75 Fahrenheit?) it ran close to boiling.

So what do I do?

I am going to flush the water system at the weekend, perhaps twice, perhaps more than twice.

I am thinking of drilling some holes in the front valance and dropping the oil coller under where it sits to get it out of the way of the radiator and allow more air in.

Is there anything else I can do? Any ideas ratefully received!

Thanks,
John.

P.S. This BBS still thinks I'm in Middlesex, I never have been and I'm now in Yorkshire.
JW Prewer

John,

Maybe you didn't mention it as being too obvious, but I don't see any claim to changing the thermostat.

Charley
C R Huff

Charley,

You're right, I missed it, there is no thermostat. To make a blanking sleeve like the one the factory originally sold I cut the thermostat bit out of the middle to leave the outer ring.

Camshaft was orginally standard and is now and 864.

John.
JW Prewer

John,
I don't think drilling holes and moving oil coolers will fix what is obviously a different problem - my B does not overheat in 42 deg C temperatures, even with 9.3 compression, large valves, cam etc.

Is there a possibility that you have a blockage somewhere in the 18G block you fitted?

David
David Overington

John

The engines do run a bit hotter on unleaded but not that hot.

First are you sure the gauge is reading correctly?
sounds more like a timing/carb set-up problem more than block blocked,

Second did you fit a new pump as impellor could have come loss even on a new pump.

Third try running water wetter and with the heater full on to see if that makes it run cooler.

Ste
Ste Brown

I would consider installing a normal thermostat. It is possible that the coolant is circulating too fast and not allowing the radiator to do it's thing.
Sandy
Sandy Sanders

Based on your discription of events, the problem started when you switched to the unleaded cylinder head. Perhaps something is wrong with it.

Wayne
Wayne Pearson

Wayne,

Good point. I know that the oil ways that lubricate the rockers changed during the lifetime of the MGB, so you need the right rockers posts for the cylinder head, but did the waterways change? I can't recall ever hearing that they did.

John.
John Prewer

John,

I would suggest putting a proper thermostat in it, if for no other reason than to get to eliminate that as a variable.

When you cut your existing thermostat, did you cut the old style that was like a sleeve/cup, that blocks the bypass ports in the head, or did you cut one of the common disc style?

Like David, I think the modifications you are contemplating should not be needed for your operating conditions, and if they help, they are only masking the underlying problem.

Charley
C R Huff

The cooling system is pressurized to change the boiling point so any coolant leak will cause a boil up. It only needs to be a pinhole.Maybe across the cylinder gasket.
Getting hotter with a new distributor may be a timing fault.
Ed
Ed Campbell

Overheating can have many, many causes. I would agree with the suggestions to fit a proper thermostat. Pre-ignition needs to be ruled out as this can cause other problems as well. You normally have to retard the timing when converting and using un-leaded. A weak mixture will also cause overheating by raising combustion temperatures, so check the mixture. Binding brakes will also raise running temps.
As an experiment retard the igntion 2 degrees, richen the mixture by one flat of the mixture nut and check the brakes.
Al
Allan Reeling

Curiouser and curiouser...

I cleaned out the cooling system on Sunday with a 2 part cleaner by Holts. This began with 30 mins at tickover and it didn't overheat! Part 2 included 15 minutes at fast idle (a steering lock leaning on the throttle pedal!) and it got hotter, but still not badly (a tad over 190 degrees Fahrenheit). This was running the car's 1960's Kenlowe electric fan.

According to the instructions I was supposed to flush through the system until the water coming out was clean, I did this but no muck came out at all.

All in all I expected serious oveheating when I ran the car on the driveway for the over an hour at tickover/fast idle & got none.

Guess what? I did have a themostat! I have just been fiddling with this car for too many years (27), I'm getting older and forgetting what the heck I've done to it!

Part of the cleaning process was to stick a hose pipe in the thermostat housing and flush water through the opposite way from normal. When I took the housing off the thermostat was open & looked OK, but I took it out anyway for the moment.

Tonight I'm going to take it for a run to the filling station and see what happens. If it gets hot it may be time to change the timing...

John.

John Prewer

John,

Overheating can ruin a thermostat. I would still put in a new one.

Charley
C R Huff

John, Keep a record of what you have done to your car. I wrote a program for my computer in 1983 and have records on my B going back to the first entry. I'm getting old and forgetful so I don't want to miss any repairs that I have made. RAY
RAY

Everyone,

Thanks Guys! All advice very much appreciated!


Ray,

The trouble is my list of things to do gets longer than the list of things I have done - that's how I am in this mess!

Until my Daughter was born I had 16 years when I could rely on my MGB (after 1 year of rebuild). Then a few niggles and far less use over about six years, then we abandoned leaded fuel in the UK, I moved house which got me lots of other things to do, and as a result here I am...

I still have a bent wishbone pivot arm (the one the wishbone bushes fit onto) to replace, and not the foggiest idea how I managed to bend it!

Also A back shock absorber link rattles because it wasn't done up well enough and then its bolt seized solid. Cutting it off and replacing it is a winter job.

And I still LOVE these cars!

John.
John Prewer

SORTED!

I had the radiator re-cored (well, the spare old radiator actually!) and the jobs is a good one!

The car now runs 40 degrees Fahrenheit cooler in an air temperature less than 10 dgrees F cooler than when I had the problem.

I went to a local radiator specialist who offered me a four row re-core for £70 or "the business" for £90 so I went for the latter (Someone told me ages ago that MGAs were 2 core as standard and MGBs 3 core).

The radiator which was the problem I had bought from a trade stand at an MG event and was done by a nationwide supplier, which the trade see as pretty poor. The nationwide supplier sounds like "Jerk" if you know what I mean...

Signing off on this thread (and on to those suspension jobs I still have to do!)

Thanks,
John.
John Prewer

"sounds like "Jerk" if you know what I mean"

Same situation as 'sh*t-fit', the tyre fitters, then ...

You would probably have been OK with a good 3-row. With my V8 running hotter than I would have liked I plumped for a 4-row over the standard 3, but was disappointed with the results. It wasn't until I beefed up the electrics for the cooling fans that I resolved it.
Paul Hunt

This thread was discussed between 17/06/2009 and 08/07/2009

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