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MGB 1976 MGB Runs Hot

ScotStern

Member
Offline
My problem is as follows:

When I am on the freeway....no problem. The cars runs with the needle on the "N".

When I am in traffic or just ideling the needle is higher...around a needle's width away from the "H".

The radiator is farily new and the coolant was just changed. Outside tempature is around 75 degrees.

Any thoughts?

Scot Stern
1975 and 1979 MGB
 

tony barnhill

Great Pumpkin - R.I.P
Offline
First, MG's didn't run hot from the factory....there's nothing inherently wrong with the basic design - its just been used for 30-something years...here's a run down of things to do/check:

1. Backflush the block - if that entails removing the freeze plugs, so be it.

2. Replace all the hoses - they're probably weak on the inner walls after all these years

3. Remove the heater core & flush it (oh, replace those hoses also)

4. Check the operation of the heater control valve

5. Thermostat

6. Are the fans operating properly?

7. Water pump - is it still doing everything its supposed to? If its old, replace it.

8. If your car had it originally, is the mud guard still between the radiator & front of engine

9. If your car has a complete radiator support panel, is the foam still between the radiator & it? Is the rubber still attached to the top of it?

10. Did I mention the radiator cap? No, replace it.

Basically, you want to ensure every piece of the cooling system is working as designed....
 

RF Thom

Jedi Hopeful
Offline
Scott

Sound like you have a water pump problem. Check the slip distance on the pump - that's the distance from the impeller blades tips to the angled face. It should be 0.012" max. If it's larger than 0.012" then at low speeds the coolant is lazy and flows around the impeller blades rather than going out into the block - thus low or no flow with resulting overheating. At higher speeds this slip as a protion of overall flow is reduced thus temperature returns to normal range. I discovered this condition by accident. A client had his engine overheat while idling pumping heating oil and crack the block. We put another engine in the vehicle - same thing. "What is similar and what is different" - as we were transferring parts from engine to base engine. We took the pump off and sure enough he had replaced the pump [leaking seal] the week before at a different repair shop out of town where the breakdown occurred. I put the pump on the bench and with a socket over the pump shaft reset the impeller to the 0.012" spec. - the truck now runs cool irrespective of engine speed.

Regards, Bob
 

jaybird

Yoda
Offline
We've had the same issue with Emma. Only she runs HOT all the time, 1/8" from H. Even in the cooler weather, she runs just past the N. Radiator was pressurized and flushed, all hoses changed out, dahubby fabricated a mudguard/pan, put a new radiator cap on, and we changed from a 185 to a 160 thermostat. Didn't solve the issue. We just replaced the water pump yesterday. IF that doesn't help, we'll flush the block and heater core.
 

tony barnhill

Great Pumpkin - R.I.P
Offline
All the 'bandaids' that people do to stop an overheating problem usually exaccerbate the problem down the line....you don't need extra electric pusher or puller fans bolted through the radiator, you don't need larger radiator, you don't need to drive without the thermostat....all you need to do is get your cooling system in the same working condition it was in when the car was new...

...I don't have overheating problems!

Sorry, rant over.
 

jaybird

Yoda
Offline
I have an oil cooler here that we intend(ed) to put on Emma. Should we still go ahead and do that, or wait to see if the problem's solved with the water pump and/or flushing the block and heater?
 

tony barnhill

Great Pumpkin - R.I.P
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Did Emma come originally with an oil cooler? If not, why do you need one now?
 

jaybird

Yoda
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Umm, because a guy in the club (several) said it might help. And because a guy gave us one?

I get your point. We should give the oil cooler back, huh?
 

tony barnhill

Great Pumpkin - R.I.P
Offline
No, install it if you want...it hangs upside down under your radiator panel...it'll keep the oil cooler...however, in Illinois winters, it might keep it so cool that your engine never warms up!
 

jaybird

Yoda
Offline
Perhaps we should wait and see what the water pump does. In our winters, overheating shouldn't be an issue, wasn't last winter.

Oooh, forgot to tell you. That gas tank in Binabox had 5 or 6 gallons of gas in it. We drained it out today. I was amazed. There was no residue or sludge in it, it wasn't muddy or murky. Looked like it was just pumped. Even the last few drops. I wasscared to look what might have come out of there!

So I dumped it in Emma.
/ubbthreads/images/graemlins/laugh.gif
 

tony barnhill

Great Pumpkin - R.I.P
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OOOOHHHHH...get some Stabilizer in there with that old gas....it might be good but why take a chance...also add a can of HEET.
 

jaybird

Yoda
Offline
Gotcha.
/ubbthreads/images/graemlins/devilgrin.gif
 

R6MGS

Yoda
Offline
[ QUOTE ]
All the 'bandaids' that people do to stop an overheating problem usually exaccerbate the problem down the line....you don't need extra electric pusher or puller fans bolted through the radiator, you don't need larger radiator, you don't need to drive without the thermostat....all you need to do is get your cooling system in the same working condition it was in when the car was new...

...I don't have overheating problems!

Sorry, rant over.

[/ QUOTE ]

/ubbthreads/images/graemlins/iagree.gif It's amazing the lengths I've seen people go to stop an MG from overheating....I've actually never had any serious overheating problems(on a british car), but then this IS canada.
 

Guinn

Jedi Warrior
Offline
Hi, Jay, One thing I learned in AF Instrument school: Whenever you have a consistent out of range reading, swap in a known good instrument if possible. Often this saves a lot of tinkering. Actually, I did learn a little more, but it has been a long time ago.

Guinn
 

jsneddon

Jedi Knight
Offline
[ QUOTE ]


Hi, Jay, One thing I learned in AF Instrument school: Whenever you have a consistent out of range reading, swap in a known good instrument if possible. Often this saves a lot of tinkering. Actually, I did learn a little more, but it has been a long time ago.

Guinn

[/ QUOTE ]

Agreed.

but since a known good instrument probably isn't at your fingertips....

Before you do anything else: Take off the radiator cap while cool. Stick a good thermometer in the radiator. Let the car warm up and see what the temp reads. I'm not sure on a B but N on a TR (a "real" car) /ubbthreads/images/graemlins/smile.gif is about 180 - 185. Or go down to Radio Shack and get a fancy IR spot thermometer for 50 or 60 bucks and point it at the thermostat housing.
 

jaybird

Yoda
Offline
Can I use my kitchen thermometer? It's 35 degrees right now, surely you don't mean check it when it's THAT cool? Should I run her 10-15 minutes then let her cool?
 

DART

Darth Vader
Country flag
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JB-I think the cool part had to do with safely taking the cap off. Any thermometer that reads to 212 should work, I should think. And I don't quite buy Tony's assumption all LBC's were properly engineered to run cool in hotter US climes. An electric fan addition is almost mandatory in a Dart. /ubbthreads/images/graemlins/cheers.gif
 

jsneddon

Jedi Knight
Offline
[ QUOTE ]
Can I use my kitchen thermometer? It's 35 degrees right now, surely you don't mean check it when it's THAT cool? Should I run her 10-15 minutes then let her cool?

[/ QUOTE ]

By cool I mean don't open the cap off when the car is at temp. You might get a nice Glycol Facial.
 

jaybird

Yoda
Offline
Gotcha. But opening it right now won't determine anything. I'll take her for a drive this afternoon, let her sit a bit, check her temp and report back.
 

Nunyas

Yoda
Offline
JB: I believe the way to do this is open the radiator. Start the engine and let it idle. Place the thermometer in to the radiator cap hole and watch the temp. Let the car keep idling until the in car guage reaches the point that you normally see it when driving around, assuming it doesn't start boiling before then (it shouldn't).

The temp should rise relatively quickly when the thermostat opens to let the coolant flow.
 
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