Overheated, Now Dies When Warm

magnet18

Active Member
Jul 16, 2012
38
16
28
Northeast Indiana
The issue:
I had the engine running great, drove the car for a few days until one day it overheated idling.
It did not boil over, it just started to lose power and died.
Now it's a hard(er) start, and once it warms up (not hot, just warm), it loses more and more power until it dies. Did I kill my heads? Overheat the C4 tranny?

Odd: idle in park has always had to be ~1500 RPM to idle at ~900 in drive

Help troubleshooting please. I've never had a carbd engine, or an automatic tranny, or an engine overheat. Obviously I can change stuff to prevent it overheating in the future, I don't know why it's dying though.



A little background:


Bought a 78 mustang with a rebuilt engine not yet all the way broken in, block out of a 79 5.0L, cams and timing are correct for regular 302 (not HO)

Automatic transmission, stock C4 from the 78. Sometimes I need to put it in 2 before it will engage.

Ran rough no power backfiring all the way home (it was cheap, I knew what I was getting into)

Got it aligned, the shop took a quick peek at the engine, checked compression, and recommended running the valves.


What I have done so far:

Pulled the leaking heater core and replaced it with a short length of hose. (before any of this)

Fixed the choke wiring

Loosened the rockers and re-torqued to 20 ft-lbs spec (proper process, pushrods down, etc.)
This got it running great!

However, idle seem weird, it needs to be quite high to maintain 900 in drive. I've never had an automatic vehicle before, don't know if this is normal for a C4.
 
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Sorry, holley 4 barrel carb naturally aspirated and a compatible intake (don't know the speck on the intake off the top of my head, nothing super fancy)

No emissions stuff or AC

Got a GM power steering pump on it of some sort but I think that's a common mod

Dual exhaust nothing fancy

currently missing kickdown linkage

I think everything else is stock
 
First off I think the missing kick down linkage is a problem, not sure, it has been awhile since I fooled around with automatics.
More important I think we need to move this to the mustang II section for help with people with similar setups, and welcome to stangnet.
 
First off I think the missing kick down linkage is a problem, not sure, it has been awhile since I fooled around with automatics.
More important I think we need to move this to the mustang II section for help with people with similar setups, and welcome to stangnet.
Kickdown isn't necessary on a C4, it just won't downshift at WOT. I don't run one on my car, I just slap the shifter around as needed (Hurst ratchet shifter).

To OP:
Post some pics of the engine, carb and intake in particular.
 
Kickdown isn't necessary on a C4, it just won't downshift at WOT. I don't run one on my car, I just slap the shifter around as needed (Hurst ratchet shifter).

To OP:
Post some pics of the engine, carb and intake in particular.
You like slap'n things around? Hummm, and how does that make you feel?
I suspect pretty good when it involves second gear rubber?
 
Sorry for posting in the wrong place, I figured 79 engine foxbody section, oops

What you say matched what I've heard, kick-down is just a convenience, not necessary. Like you said, stick it in low for some fun and bump it to drive when you get going

I'll get some pics posted up
 
Sorry for posting in the wrong place, I figured 79 engine foxbody section, oops

What you say matched what I've heard, kick-down is just a convenience, not necessary. Like you said, stick it in low for some fun and bump it to drive when you get going

I'll get some pics posted up
No worries, I'm one of many here that can help put things in the right places although I'm often confused, but I do live in Florida so I guess it would be natural.
@74stang2togo is the one that set me straight on the linkage thing, he be one of the resident ll experts.
 
Here's a few pics, black on the carb was there before from the backfiring issue
 

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ok, here is my opinion on electric fans, the stock fan clutch setup is great at cooling and if by chance should fail it locks the blades so it will continue to operate pulling air through the radiator, if an electric fan fails your SOL for the most part. They do work great and failure rate for quality stuff is small but the electrical system needs updated with a larger amp. alternator and corresponding wiring, it's not difficult to upgrade and does add a few ponies.
I have mixed feelings on aluminum radiators, but is a good investment if future horse power is planned, just don't stick a aluminum one in thinking it will resolve a overheating problem unless of course yours is failing now.
check your timing, if you don't have a timing light it is a good investment or you could borrow one from a friend or some parts stores have a loaner program, you have a vacuum advance distributor so you have to make sure it is working correctly, get a repair manual to show you what port the vac line go's to and what the specified settings are,
keep us posted, hope this helps.
 
That's all solid advice that I'll keep in mind, thanks, but I don't understand how it applies to my current troubleshooting, unless overheating can mess up the vacuum advance.

  • For about a week it ran great, started fine, 70 on the highway or sitting at a stoplight, everything was fine.
  • Then it overheated (this is not my problem, I can replace parts and make upgrades to prevent this in the future)
  • Now the moment the engine gets a bit warm it starts losing power, and just get's worse until it dies

what could have overheating have changed? Warped rods or something?

I have a manual and can get a timing light, I'll check out the vacuum advance.

Thanks again for the help
 
never heard of overheating warping rods. there are differences in the electronics between the cars I have and yours, how hot does it get? heat can effect several things like fuel, electronic control box, plug wires. do you have a manual fuel pump?
someone with more experience with this type of electronic ignition will chime in soon.
things I would check:
thermostat - flow through the radiator- condition of the spark plug wires - coil - brain box
your coil can be effected by heat, also the brain box, causing weak spark, loss of power.
 
That's great to hear, thanks!
Everything under the valve covers is uncharted territory for me, so I was really hoping I hadn't ruined something in there. Heads, carb seal, gasket, valves, etc.

She's old school, no brain box, but the iggy is original and engine mounted so if that went it would make a lot of sense, I'll give the electrical system a good going over

And overhaul the coolant system :nice:
 
Check the Duraspark box on driver's fender.

Mustang II engine compartments don't evacuate heat very well, and if it overheated, the resin in the Duraspark box could have melted, which result in a loss of power and stalling when warmed up even though it would start just fine while cool.
 
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