[jchilds]

I have about 300 miles on my new 351C and am experiencing a problem that I have had in the past with other new motors. Can someone tell me what exactly causes this: If the engine is cold, the thing cranks over great. If I drive it a few miles and stop, it will crank right back no problem. If I drive it about 20 miles and stop then try to re-crank, it really struggles to turn over; a couple of times I had to wait a while to get it started again.

Is this a heat problem? My temp gauge never goes over half way up, and I have a 4-core radiator and a new sending unit. I know the gauge works because before I got the big radiator it would overheat regularly.

Or, is this some other problem altogether?

 

[Ernie]

Sounds like a vapor lock problem, I'd also make sure my timimg was not too far advanced.

 

[mike65]

jchilds,
I had a similar problem with a 68 302 engine. When it was cold it started fine, when it was hot cranked very slowly almost like it had a weak battery. I found the starter had high resistance. I replaced the starter & all was fine. Hope this helps.

 

[jchilds]

I have a new starter.

Also, why would vapor lock make the motor crank slow?

Finally, why would the timing being too far advanced let it start OK cold then not when it is warm? It seems fine when it is just warmed up; the problem only starts when it is just a little warmer.

If this is vapor lock, what is the best way to get rid of it?

 

[Axnjxn]

Your starter may be new, but my money is still on it as the culprit. Are you running headers? If so, how close do they get to the starter? The hotter the starter gets, the more resistance it will build up. It will take a while, 20 min + for the starter to start getting heat saturated.

One possible diagnostic techque would be to get an ice cold rag on the starter the next time this problem arises, and see if it cranks better. OR, the more scientific method, put an ohm meter across it. Simply put the (+) of the ohm meter on the back side of the starter solenoid (starter side) and the (-) to ground. You don't want or have to crank the engine. Compare the readings between hot and cold. To be honest, I don't know what those readings should be, but they should be relatively close to each other.

If it is the culprit, a heat shield may help a bit, but it will also trap the heat in if it's too close to the starter. You may need to have the starter rebuilt by a specialist who can install better windings.

Also, make sure all your connections are totally clean, and that ALL of the battery cables are in good shape. The resistances will add up. Add poor connections to a hot starter, and high compression, and you'll get hard cranking pretty easy.

Good luck

 

[jchilds]

Now that makes sense. I am running headers, and they are definitely close to the starter. I can probably scrape up an ohmmeter so I'll try the scientific approach. Plus, I would probably need an ice-cold rag for my hand and arm if I tried putting something on the starter when it is hot!

Thanks very much for the info.

 

[bishir]

Yeah, Chris nailed it. I was going to suggest the same thing after reading your post description. Most of the hard starting problems when it's hot are due to the poor heat resistance of the starter. There is a heat wrap you can buy that is supposed to help alleviate this problem, but if the headers are as close as you say they are then it probably won't be enough. What kind of headers are they anyway?

 

[sharkmouth]

2 other things......if the initial timing is too far advanced and ESPECIALLY IF THE IDLE MIXTURE IS TOO RICH, it can crank hard warm

 

[Guest]

first check your battery cables. Make sure they are in good shape and that the connections are really good. The same thing happened to a friend and it was his cables. Good luck