'71 Mustang ...Cold engine start OK, warm engine will not start...sluggish crank

A cold engine crank will turnover and start normally. But stop to run and errand or grab lunch…and the warm 302 2 barrell engine will turn over very sluggishly, lke the battery is dying. If you wait until the engine is cool, an easy start is assured but that takes hours! A local repair shop has rebuilt the carb, the battery & cables are new, and the starter works fine when engine is cold. Any suggestions as to the problem?? My local repair shop is out of suggestons. It seems to help a little to hold the gas pedal down on the floor for a warm engine start…but engine still turns over sluggishly when trying to start when warm. HELP! Now If I drive it…I just drive it around town a bit then back home …unless I stay several hours somewhere while the engine cools…but that’s not fun. It is a convertible, fun to drive…and this problem needs to be solved. Any ideas would be appreciated.


ford starters tend to distort when hot when they get old. they bind up inside until they cool off again and the metal contracts enough not to bind up.

when this happens they crank really slowly when hot, almost like the battery is dead. usually after 35 or 40 minutes it will start again.

or would you believe that it means that your engine is blown and sell me that mustang real cheap? :slight_smile:

just kidding. buy a new starter and I bet your problem disappears

I have had this same problem on two different cars and the causes were different.

#1 1974 Chevrolet Monte Carlo with 400 cid engine–the battery did not produce enough power. It takes more power to start a hot engine than a cold engine (not extremely cold). A new battery did the trick.

#2 1988 Ford Taurus with 3.8 liter engine. Solution was a new starter.

The test is to measure the current draw when the engine is hot and turns over sluggishly.

Quoting @wesw " ford starters tend to distort when hot when they get old. they bind up inside until they cool off again".

A lot of us are like that as we get older.

BTW, you nailed it. It’s almost certainly the starter. Do as @Triedaq says and get it checked.

Check the timing. If it’s advanced too far the starter will labor to turn the engine over when it’s hot.

The above, and is the choke off when warm?

@Rod Knox made a good suggestion. In my advanced years, I forgot that cars in 1971 did not have computers to control the timing. When the engine is hot and cranking slowly, try retarding the ignition timing and see what happens. Also, as @texases suggests, check to be sure the choke is fully open when the engine is warm.

You could get a starter or make a heat shield. A muffler clamp and two holes in sheet metal is the basic item. You can glue heatproof gasket material on the sheet metal but it’s not really needed. High temp RTV if you go for the luxury model.

I had the same problem with my 1971 Mach 1. New starter, new solenoid, new heavy duty battery. Problem solved.

In addition to the above suggestions I might add…

Has the engine been rebuilt? If piston clearance is inadequate, they can get tight when hot…This is a long-shot but possible…Also, remove air-cleaner and look down carb throats when engine is warm… Do you see ANY sign of fuel leaking or dripping inside carb??

Your starter can be tested for amperage draw under both cold and hot conditions. The readings should be the same…If it’s pulling many more amps when hot, then something is dragging on the engine. If the hot draw is LESS than the cold draw, then the starter should be replaced…

if the starter is binding inside because of distortion it will draw more amps not less. testing the starter when cold may not find the fault in it as they only bind when hot in the situation I described first about ford starters. when I first encountered this prob on my old ford only the old fellow at sears, mr goodwrench, that a friend of mine knew, had the experience to diagnose it without extensive exploration

GM mechanics are VERY familiar with this as heat-soaked starter failure is common in Chevy V-8 powered cars…Not so much in Fords…It depends on exhaust manifold and pipe design…Missing heat shields can also play a role…The OP mentioned a rebuilt starter. I have little faith in those…

I saw nothing in his post about a re built starter, just that it worked fine when cold…

Having learned the hard way that rebuilt anything can be a crap shoot I installed a new starter in my Mach 1 even though it cost about twice as much as a rebuilt. It was something like $40! I had to go back and look. OP mentioned a rebuilt carburetor and new battery and cables.

I had problems with a rebuilt starter that I purchased from Western Auto and installed by its service department. The car was a 1988 Taurus with the 3.8 liter engine. The engine would barely crank when it was hot. Western Auto claimed that they could not duplicate the problem. In desperation, I took the car to an independent shop where I had never done business. The car was hot and when I shut it off, the starter would barely crank the engine. The shop owner measured the current draw as I attempted to start the car. He then disconnected the engine and had me again crank the engine. The engine barely cranked with the ignition disconnected. He noted the current draw which he said was excessive. He noted the current draw on his shop’s stationery and told me to take it back to Western Auto. There was no charge. When I showed the results to Western Auto, they immediately installed another starter and I had no problems after that point.
This occurred 19 years ago. I have been a customer of that independent shop since that time.