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Overheating frustration

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Overheating frustration
#1
jlesh Jack Lesher (New Member)
Stevens, PA, USA   USA
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Hi everyone,
I bought a 75 mg midget 1500 not too long and have been rebuilding it. It has been going well by all accounts, except for the cooling system. Every time i run the car (not driving it yet) it seems to overheat. When i bought it, the radiator was cracked and thermostat was shot, replaced both of those. Filled up the coolant and it still overheats, I could really use any sort of advice. I have read through a lot of these forums about similar issues but cant seem to figure it out. Could it be my water pump? Thanks everyone in advance.

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Re: Overheating frustration
#2
JAMADOR Avatar
JAMADOR John Amador
Spring, TX, USA   USA
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1975 MG Midget 1500 "Midge"
Is the fan engaging? On mine, the clutch was bad. Replaced it with a direct drive Spitfire water pump & fan.


1975 MG Midget 1500 - Midge
Work in Progress

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Re: Overheating frustration
#3
jlesh Jack Lesher (New Member)
Stevens, PA, USA   USA
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Yes, the fan does engage which only adds to my confusion.

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Re: Overheating frustration
#4
ken472 Avatar
ken472 Ken Petersen
Superior, WI, USA   USA
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1973 MG Midget MkIII
Are you sure you got all of the air out of the system. Could be an air lock. The vanes of the water pump could be worn as well or did you put in a new water pump?



Edited 1 time(s). Last edit at 2024-04-14 07:51 PM by ken472.

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Re: Overheating frustration
#5
refisk Rick Fisk
Frankenmuth, MI, USA   USA
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Incorrect timing and/or a lean carb mixture can also cause overheating.

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Re: Overheating frustration
#6
jlesh Jack Lesher (New Member)
Stevens, PA, USA   USA
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I am fairly sure i did a good job of getting air out of system when refilling, but i am all for double checking, what is the best way to check/ get any extra air out?

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Re: Overheating frustration
#7
jlesh Jack Lesher (New Member)
Stevens, PA, USA   USA
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The mix from the carb should be good, i just got it rebuilt, timing i am not certain, but the heat seems to build up very quickly, can timing do that?

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Re: Overheating frustration
#8
ice Avatar
ice Gold Member Larry Ice
Lawrenceville, GA, USA   USA
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1971 MG Midget MkIII
If the car came with a leaking radiator the engine may have overheated and damaged the head. Check for oil in the radiator and look for whiteish smoke coming out to the exhaust pipe.

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Re: Overheating frustration
#9
ken472 Avatar
ken472 Ken Petersen
Superior, WI, USA   USA
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1973 MG Midget MkIII
One way I try get the air out of the system is to loosen the return line from the heater while the engine is running to let the air out

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Re: Overheating frustration
#10
Wellkevi01 Avatar
Wellkevi01 Gold Member Kevin Wells
Midland, MI, USA   USA
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1978 MG Midget MkIV
Another question is how are you verifying that it's overheating?

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Re: Overheating frustration
#11
refisk Rick Fisk
Frankenmuth, MI, USA   USA
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I believe on a 1500 you leave the small brass fill cap off and run the engine until all of the air is burped out of the system.

In reply to # 4785184 by jlesh I am fairly sure i did a good job of getting air out of system when refilling, but i am all for double checking, what is the best way to check/ get any extra air out?

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Re: Overheating frustration
#12
opieshuffle Avatar
opieshuffle Chris Elkerton
Toronto, ON, Canada   CAN
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1975 MG Midget MkIII
My vote is:

1. Air still in the system. (pull the filler plug at the top fill... then leave overnight... you'd be amazed at how much air works its way out this way) Top up and try again... this method has never failed me
2. Timing: I can't tell you HOW LONG I chased down the problems of my overheating Midget 1500 until I got a timing light and re-set it. (if all the smog stuff is gone, set it to 10 BTDC. I did and haven't touched it since)

C

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Re: Overheating frustration
#13
JAMADOR Avatar
JAMADOR John Amador
Spring, TX, USA   USA
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1975 MG Midget 1500 "Midge"
In reply to # 4785299 by refisk I believe on a 1500 you leave the small brass fill cap off and run the engine until all of the air is burped out of the system.

In reply to # 4785184 by jlesh I am fairly sure i did a good job of getting air out of system when refilling, but i am all for double checking, what is the best way to check/ get any extra air out?

That's how I did mine, when I replaced the water pump.


1975 MG Midget 1500 - Midge
Work in Progress

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Re: Overheating frustration
#14
Mtn Sprite Avatar
Mtn Sprite Layne M
Santa Cruz, CA, USA   USA
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1969 Austin-Healey Sprite
Very rapid overheating is often a blown head gasket from a compression chamber to the water passage leak.
Some mentioned white smoke which may or may not occur in that case.

-Do you have any rapid bubbling or surging of the coolant at the cap?

-Mentioned above,

-How do you know it’s overheating, gauge or behavior characteristics?
-What are those characteristics?

-Yes, Retarded timing can cause overheating, more when driving than idling . As above check it.

-Lean running overheat is usually an overheat problem when driving, not idling but just because it was rebuilt doesn’t mean it’s tuned properly to your engine.

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Re: Overheating frustration
#15
jlesh Jack Lesher (New Member)
Stevens, PA, USA   USA
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So I know it is overheating just by the gauge, but also the engine tends to run on after shut off, but only does this if i run it long enough to see if it is overheating with the gauge.

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