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overheat
#1
  This topic is about my 1963 MG MGB MkI
ringmaster2000 Silver Member Will Ring
Lake Stevens, Washington, USA   USA
It was a beautiful day here in the northwest (not raining and 70 degrees) So i took the B out for a drive. mostly on back roads, except for a short jaunt on the freeway at 60 on the way home. It ran perfect, just that steady thrum...... I stopped a light about 2 blocks from home and all of a sudden the temp gauge started to rise from the normal 180. by the time i got home a block later it was 220. I turned it off and checked under the hood, it didn't seem really hot, but i let it cool down. I started it a hour later after checking the radiator and refilling . it just ran like normal, but it heated up REALLLy fast

1. no steam or any odd things from tailpipe
2. ran good both before and after
3. no leaks under the car of coolant

Can't imagine a bad thermostat. so have i blown a headgasket???? sprayed the bolts on the thermostat housing just in case i need to check that first.

Thanks - will

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lgorg Avatar
lgorg Larry Gorg
Renton, WA, USA   USA
1966 MG MGB "Robbie"
Will,
If its any consolation, my 67 does the same thing, especially, if you run it at freeway speeds and run into traffic off the freeway. I am running a 25/75 mix of anti-freeze to water, and it still does it, but a lot less than when I used a 50/50 mix. The PO told me that it does not like sitting in traffic. At speed, the air pushing through the radiator cools. When you stop at a traffic light, all it has, is the mechanical fan, and that is the original 3 blade metal fan. I simply try to keep the car moving to keep the air moving through the radiator.

J Baz Avatar
J Baz Silver Member Jerard Basmagy
Middletown, New Jersey, USA   USA
In reply to # 3508860 by ringmaster2000 It was a beautiful day here in the northwest (not raining and 70 degrees) So i took the B out for a drive. mostly on back roads, except for a short jaunt on the freeway at 60 on the way home. It ran perfect, just that steady thrum...... I stopped a light about 2 blocks from home and all of a sudden the temp gauge started to rise from the normal 180. by the time i got home a block later it was 220. I turned it off and checked under the hood, it didn't seem really hot, but i let it cool down. I started it a hour later after checking the radiator and refilling . it just ran like normal, but it heated up REALLLy fast

1. no steam or any odd things from tailpipe
2. ran good both before and after
3. no leaks under the car of coolant

Can't imagine a bad thermostat. so have i blown a headgasket???? sprayed the bolts on the thermostat housing just in case i need to check that first.

Thanks - will

You say you refilled the radiator after cool down, so you have to be losing it somewhere. I would start with a pressure test of the system to figure out where it's going first. I would confirm the pump is pumping too by starting the car with the cap off and watch for the flow when the thermostat opens. BTW how's the oil does it have coolant in it? Another thing use a infrared thermometer to confirm temps of the coolant could be as simple as a bad sender. jb

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B-racer Avatar
B-racer Jeff Schlemmer
Minnesota, USA   USA
Lean mixture and retarded timing (less than 10-12 BTDC) at idle can do this.
For it to "pop up" out of the blue I'd suspect a stuck T-stat first, but that could happen at any speed.



jeff@advanceddistributors.com

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Before you do anything, check the level of coolant. If it is too low after refilling, then the sensing bulb below the thermostat housing may be exposed to air rather than liquid coolant, which will afford an inaccurate reading.

If the problem persists, next step is to check various places on the engine and radiator with a non-contact infra-red thermometer to confirm whether your car is indeed running hotter than normal...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

lgorg Avatar
lgorg Larry Gorg
Renton, WA, USA   USA
1966 MG MGB "Robbie"
I will agree with Jeff about checking the timing. I have not yet invested in a timing light, and have to resort to borrowing one. The next item on the things to do, is re-time the car with a light to see where its at. I've been doing the timing by ear and seeing how the adjustment plays out.

If you refilled your radiator, do you have an overflow bottle? On our early cars, you can not actually see the water level. The car will toss out what it doesn't need out the radiator overflow along the highway. You come along, and decide that it "lost" water and add some, thinking it low. The car puts water in the overflow when it does not need it, and will bring it back into the radiator upon cool down.

This was the main reason why I put a clear bottle at the end of the radiator overflow pipe was due to not being able to see the water level. Just because you put water in it, does not mean that it is needed. It will dump the excess water it does not need the next time you warm the car up.

spikemichael Avatar
spikemichael Platinum Member Michael Caputo
Aberdeen, WA, USA   USA
1973 MG MGB "Freebie"
1973 MG MGB
1974 MG MGB "Spike"
1979 MG MGB "MegaBeanie"    & more
Air bubble in the water jacket.

Thermostat

radiator blockage < when the engine is hot feel the radiator, see if you have cold spots.



Michael J. Caputo
'79 RBB and '73 CBB owner with extensive experience in 12v Audio System design and installation.
Vendor of Regalia and Promotional Products. Forum Member with a warped sense of humor.


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perfectpitch Avatar
perfectpitch Charles Windsor (Disabled)
Disabled Account, Antarctica   ATA
3X about timing advance check. Could be timing not advanced enough (retarded) at idle, from what you describe. Plain water has better heat transfer (like 40% better) compared to heavy coolant ratio's. If timing advance checks out working right, you might try about a 20% coolant to 80% water. If the timing advance off even 5 degrees (retarded or not enough advance) at idle it could make it overheat. Curious why you think it not likely at all the thermostat. Did you change it recently? Did you use the correct type or same as before when it not overheating? Any other changes before/after overheat?

ringmaster2000 Silver Member Will Ring
Lake Stevens, Washington, USA   USA
Okay i feel so foolish, but in the interest of being above board here we go. I have been spraying the thermostat nuts with PB blaster every day, i wanted to make sure they were ready to break free on this early B. So i went out to do my daily spray, and oddly enough just looked straight down, and found the generator pulley had self destructed, and there sat the belt. Oh my, where is the part that separated from what was left of the pulley? no marks on the radiator, so not a clue.

So now looking at sourcing a new generator pulley/fan. anyone out there have one???


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ringmaster2000 Silver Member Will Ring
Lake Stevens, Washington, USA   USA
Okay finding a pulley seems harder than i thought. anyone have one i could purchase? I have seen several for sale, but they all seem to have a different pulley fan combination, longer snout for fan, or much wider pulley. Thanks, just for info its a 1963 MGB. with early 3 main engine.

Also since i don't have a picture from before it self destructed, anyone have a picture of what it is supposed to look like????

thanks

ClayJ Avatar
ClayJ Silver Member Clay Johnston
Mt. Olive, MS, USA   USA
1972 MG MGB
Might consider pulling the alternator and taking to a automotive electrical shop for evaluation and pulley replacement. They might also just give you a suitable pulley off an old unit.

One thought, will the alternator shaft turn easily? I'm wondering if the alternator froze/semi-froze and the stress broke the pulley.

dickmoritz Avatar
dickmoritz Gold Member Dick Moritz
Philly 'burbs, PA, USA   USA
Generator, not alternator...

Dick

In reply to # 3514713 by ClayJ Might consider pulling the alternator and taking to a automotive electrical shop for evaluation and pulley replacement. They might also just give you a suitable pulley off an old unit.

One thought, will the alternator shaft turn easily? I'm wondering if the alternator froze/semi-froze and the stress broke the pulley.



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

perfectpitch Avatar
perfectpitch Charles Windsor (Disabled)
Disabled Account, Antarctica   ATA
A bit hard to believe the engine ran very long with the belt just sort of riding on top of things without getting all tangled up.

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