Author Topic: Overheating issue 69 Mustang 428CJ  (Read 208 times)

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Offline Steve69Mach1

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Overheating issue 69 Mustang 428CJ
« on: July 02, 2018, 08:40:13 am »
Acquired a 69 Mach1 428CJ  ground up restored..Date Correct engine.(identical to one I drove in High School) that overheats after about 10 minutes of driving or idling. Is AC equipped. Have tried thermostats from 165 to 185. Fan and clutch seem OK and has a shroud. Oil pressure gets low and severe starter drag on restart. Using 50/50 coolant.  Any suggestions would be appreciated.

Offline sah62

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Re: Overheating issue 69 Mustang 428CJ
« Reply #1 on: July 02, 2018, 09:24:05 am »
What exactly do you mean when you say "overheats"? Boils over? High reading on the temperature gauge? I'm asking because many of us have been in situations where new senders seem to produce higher than normal gauge readings without the cooling system actually overheating. Have you been able to measure the actual coolant temperature? Something like this might be helpful if it's not easy to install a different sender with a real gauge:

https://www.428cobrajet.org/forum/index.php?topic=24395.0
Scott Hollenbeck
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Offline rhjanes

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Re: Overheating issue 69 Mustang 428CJ
« Reply #2 on: July 02, 2018, 09:33:37 am »
What Scott said.

An old friend of mine, who was doing motors since WWII, had several big block Shelby's advised me "an FE isn't hot until it pukes out coolant".  He also said a lot of hot issues, were timing issues.  Seems he was spot on with my driveabilty issues from 15 years back. 

Starter slow/sluggish/dragging on a secondary start, tells me the timing is probably off.  Set it to factory, and triple check that. 
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Offline Steve69Mach1

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Re: Overheating issue 69 Mustang 428CJ
« Reply #3 on: July 02, 2018, 09:50:16 am »
Will Boil over. Date correct Temp gauge and goes to H pretty quickly..Will have the timing checked.
THANKS!

Offline sah62

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Re: Overheating issue 69 Mustang 428CJ
« Reply #4 on: July 02, 2018, 10:21:55 am »
Will Boil over. Date correct Temp gauge and goes to H pretty quickly..Will have the timing checked.
THANKS!

If it's boiling over there are any number of things can contribute to the problem. Coolant being expelled from the overflow hose can be due to an overfull situation; you should only fill the radiator to the top of the fins. Poor coolant flow can be a symptom of a bad water pump, blockage in the radiator, or blockage somewhere else. Is your cooling system holding pressure? Do you have a 13 PSI cap installed? I'd still suggest getting a measure of the actual coolant temperature to help narrow down the possibilities.
Scott Hollenbeck
Administrator, Mustang 428 Cobra Jet Registry
Owner, Muscle Car Research LLC
1970 R-Code Mach 1
2006 Dodge Charger SRT8
1995 Chevrolet Impala SS

Offline Steve69Mach1

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Re: Overheating issue 69 Mustang 428CJ
« Reply #5 on: July 02, 2018, 02:45:33 pm »
13 PSI cap on.  Will check coolant temp. THANKS!

Offline preaction

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Re: Overheating issue 69 Mustang 428CJ
« Reply #6 on: July 02, 2018, 04:03:54 pm »
A good infrared thermometer is great for this.
68.5 Raven black 4sp 3:50

Offline rhjanes

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Re: Overheating issue 69 Mustang 428CJ
« Reply #7 on: July 02, 2018, 08:31:07 pm »
What Scott also pointed out about the fill level.  Big Blocks have such thermal expansion, that they can force fluid out if you over fill by much.  I fill mine about 1/2 inch above the coolant tubes which you can see down inside the radiator.  The few times I attempted to fill my big block as I do with my small block, it would get to temp and then puke out the extra.  That buddy of mine told me to just let it do it.  Clean up the mess.  After it totally cools down.  Then check where the level is inside the radiator.  IE, the big block tells you what level it will put up with!

Also, checking fluid flow.   Open the radiator cap when cold.  Start the car and just let it idle and get warm.  You should see the flow start going...then the water will start to feel warm also.  Not very scientific, but it is a check. 
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Offline rhjanes

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Re: Overheating issue 69 Mustang 428CJ
« Reply #8 on: July 02, 2018, 08:34:40 pm »
I should add, I'm in Texas.  I don't drive it in the blistering heat of a summer day (today was 101).  But once I got the fluid filled and timing correct, I drive it now when it is 90 degrees out.  The temp gauge reads at half way while moving at all.  After it is hot (10 to 15 minutes of driving) and if I sit at a light for 3 minutes, the gauge creeps up to around 3/4.  Goes down to half again once I'm moving.
But before I got the timing set and was over filling the radiator, it would peg the gauge, detonate, ping and then puke coolant!
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Offline CHOPPERS

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Re: Overheating issue 69 Mustang 428CJ
« Reply #9 on: July 02, 2018, 10:03:41 pm »
FWIW, If it's a fresh rebuild, they always run hot until broken in, Check timing, I sent out my water pump to a guy in Indiana, I think WATERPUMPMAN, I also have a 70 and put on a correct pulley, it was about an inch bigger than a 69, I switched that to a smaller 69 style...After all my messin around for a few weekends, It runs perfect...I think a good blueprinted waterpump, small pulley, timing and carb mixtures are the key, after 500 miles, mine has run perfect since.
Steve-o

1970 MUSTANG MACH 1 'Q' CODE AUTOMATIC   "Calypso"