302 vs. temperature

67rcks · Nov 9, 2010

I have a rebuild 302 that is a lot more difficult to turn at operating temperature than when cold. Is it normal for these engines? The battery is close to death. Just wondering if machining part was done right. oil pressure is around 40 lbs (cold) to 30 lbs (hot).

D.Hearne · Nov 9, 2010

Difficult to turn as in when starting it ? If that's the case, I'd look at the starter first. And the oil pressure, that's at idle, or at cruising rpms ?

rbohm · Nov 9, 2010

i agree with DH, in addition to a dying battery, you likely have a dying starter as well, or too much initial ignition timing. as for the oil pressure, that sounds good for idle up to about 2500rpm, minimum of 20psi at idle and 10psi per 1000rpm is the industry standard.

frdnut · Nov 9, 2010

rbohm said:
i agree with DH, in addition to a dying battery, you likely have a dying starter as well, or too much initial ignition timing. as for the oil pressure, that sounds good for idle up to about 2500rpm, minimum of 20psi at idle and 10psi per 1000rpm is the industry standard.

+1.....

Also check your cables and connections but I would bet on a weak starter or advanced timing...Do you have headers that run close to the starter?

coolblue65 · Nov 9, 2010

do you have long tube headers? I used to get heat soak all the time, the problem went away when I put on ceramic coated headers.

tx65coupe · Nov 9, 2010

I'm going to say its starter heat soak too, if you have headers.

67rcks · Nov 9, 2010

So, is it common for a 302 with a weak battery and/or bad starter that you start it (cold), it cranks fine. Then you drove 5 miles, turn off the engine, start it again and it cranks real bad? you imply engine "resistance" should be the same when the engine is hot or cold?

coolblue65 · Nov 9, 2010

When we talk about heat soak, it has nothing to with the engine resistance or a weak battery. The issue is that you over heat the starter motor-which is an electric motor, and a hot electric motor does not work as well as cool one. And yes 5 minutes of driving is enough to get it hot.

D.Hearne · Nov 9, 2010

67rcks said:
So, is it common for a 302 with a weak battery and/or bad starter that you start it (cold), it cranks fine. Then you drove 5 miles, turn off the engine, start it again and it cranks real bad? you imply engine "resistance" should be the same when the engine is hot or cold?

The field coils in the starter get hot and build up resistance to the flow of electricity. This has been a problem with (mainly) rebuilt starters for decades. The rebuilders seldom if ever change the field coils, and bad coils are very susceptible to heat soak. The weak battery certainly doesn't help things either. Old and/or too small cables contribute to resistance too.

horseballz · Nov 10, 2010

What is your timing set at? I would try backing it off (retarding) 2-3 degrees and see if there is a difference. Does the engine just crank slower when warm or does it seem to "grunt"/kick back on the starter?
HTH,
Gene

67rcks · Nov 11, 2010

that heat soak thing makes sense thank you
the engine just turns slow, there is a rebuilt starter and new flywheel. The timing is 18 btc idle some 35 at 3000 rpm. Yet this is nothing a new battery won't fix.

tx65coupe · Nov 11, 2010

The timing sounds a little too advanced to me. I have mine at about 14 or 15.

302 vs. temperature

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