No crank when hot.

[944 Geek]

G'day all I have an intermittent fault when starting. When the car is hot sometimes it just wont crank. It's just dead. Recent starter motor change, I have checked the electrics and there are no issues.

Even if I make direct contact between a power wire and the wire to the starter solenoid it does nothing. Then five minutes later it will start.

Anyone else experienced this?

[Pauly]

Is the starter new? I'm running one of these - http://garage.ideola.com/prod-ElectricsUpgrades.html

How is the battery? Tried a different one?

Doesn't seem like it's the alternator. 

Try turning your ignition switch slowly when it does it. It could be this. 

That's all there is to the starter system. 

[944 Geek]

Thanks for your suggestions.

I have checked everything except the battery which is charged properly.

It is weird. It only happens when hot. If I have the AC switch on or the cooling fans are running the same thing happens so it might be the battery but even when none of this is on it happens. Then about 10 minutes later it works perfectly...

[TINGY]

When you say it won't crank, do you mean you have nothing at the ignition when you turn the key and the engine won't turn over, or the engine will turn but not fire?

[tazzieman]

Did you install a brand new starter motor? Sounds like the starter is faulty.

[Dreamr]

It's possible there is a bad ground or a "break" in the circuit ..... could also be a corrosion on one of the wires to /from the starter ....

Shouldn't be too hard to eliminate either as the circuit isn't too large ....

[firstone]

Or bad earth

[Buchanan Automotive]

Is the starter motor new or is it an old ( 2nd hand ) one that you installed ?

[944 Geek]

When you say it won't crank, do you mean you have nothing at the ignition when you turn the key and the engine won't turn over, or the engine will turn but not fire?

No turn over. Even if I apply direct power to the starter motor solenoid trigger wire in the loom the start solenoid doesn't activate to turn the starter motor. I am beginning to suspect the battery even though it is only 2 years old.

It's possible there is a bad ground or a "break" in the circuit ..... could also be a corrosion on one of the wires to /from the starter ....

Shouldn't be too hard to eliminate either as the circuit isn't too large ....

I have rebuilt the loom to eliminate the bad Porsche design of multiple connections to a single circuit so I know it it isn't wiring. I am beginning to suspect the battery. Intermittent faults are a real pain.

Is the starter motor new or is it an old ( 2nd hand ) one that you installed ?

New one only 6 months old.

[TINGY]

Is it just the solenoid not working properly

[Dreamr]

In my Rodeo ute I often get a click sound for the first 8 or ten tries, then it starts fine ....  i will be replacing the starter .... I'm not thinking battery for mine or yours as when it does start there is a strong crank ....

I think Tingy is on track thinking a faulty starter solenoid ..... even new parts have weak spots.

[Timm]

You could try taking the starter out and bench testing it.

 

[vl gra]

Is it just the solenoid not working properly

I put money on that's what it will be. Common problem when hot not just on Porsches. Usually run a relay to stop voltage drop when hot.

[Buchanan Automotive]

Every Summer ( at work ) we see Porsche's that are more than 10 years old have starter motor ( not cranking ) issues , & the hotter the weather the more we see , 8 out of 10 times is just a starter motor issue , and not just the solenoid , we have had old & not that old Bosch starter motors that will experience Armature & or Field windings/Commutator issues when they are very hot ( not super common ) but we see it 

Common scenario } Hot weather , hot engine , starter motor very much "Heat Soaked"  in that particular Porsche , be it a 911 , 944 , 928 , engine is turned off & then the owner goes to start the engine "say" 5 minutes later & the starter motor does nothing , no cranking & often not even a click ( ZERO ), the owner then lets the car sit for "say " 20 minutes & all of the sudden the engine cranks over because the starter motor wants to work now 

The same car , the same starter motor , same drive time , but this time the ambient temp is 10 degrees cooler , the starter motor is still hot( heat soaked ) but not quite as bad & its just able to cope & all is well 

Two weeks ago we had a new to us customer turned up at our workshop in a 968 , he parked it outside & came in for a chat about the car & as he got in his 968 there was silence , his starter motor did not operate( very Hot day ) , so what we ( Sean & I ) usually do in this situation is to quickly isolate the issue & the quickest way is for us to tap the old stater motor with a small plastic hammer & instantly the old starter motor came to life , so we knew with this car its just a starter motor issue ( Very Very Very Very common ) when starter motors get beyond 10 years of age & thousands of heat cycles 

Other times is a combination of several factors , like } 

A )    Voltage drop to terminal 50 on the starter & this voltage drop is worse when the car in question is hot ( so this has to be checked in this condition )
        Engine cold =   Voltage supply check with a voltmeter at terminal 50
        Engine Hot ( & I mean proper heat soak hot ) = Voltage check at terminal 50 with a voltmeter , often when the car/engine is very hot there will be a" bad enough "voltage drop to terminal 50 on the starter motor 

You do not want voltage drops at Terminal 50 

B )   Poor quality Battery ( if you see the words on the battery ) = Made in Indonesia ,change battery with another as a test , because we have experienced dozens of "made in Indonesia " batteries play up intermittently over the last 2 decades ( at least ) & they all internally disconnect intermittently & then reconnect ( like a loose plate )

Note } The poor quality made in Indonesia battery , is not the fault of the Indonesians , they are just supplying what we have Demanded from them , we have demanded the cheapest ones they / anyone can supply & thats what we get , we get what we pay for ( sounds familiar doesn't it )

Note } we only supply & fit Calcium Batteries to Porsche's , they are all (Brands / Labels) made in South Korea & are fantastic 

C )  If you have the original battery cables & lugs from 1985 then this will always give issues ( I take it that the car is a 1985 ) where the battery is up front , if it is these give a lot of grief with the cable from the battery to there body & from the body to the engine , thats because they are crimped & they go high resistance in old age 

D )  Exchange / Reconditioned  Starter motors & Alternators , have we seen these play up in the first year or two ?  ( hell Yes ) , we had a customer supply a Genuine Bosch Exchange Alternator for his 951( from the USA) just before Xmas & its failed last week  ( Thank GOD we did not supply it )  , you can see we are seeing a bit of this stuff & we stopped supplying this stuff some time ago because of quality controls with Starter motors & Alternators 

F )  We see quite a few failures of the completely different after market "New " starter motors in the last 3 years particularly & again mostly in hot weather 

Just because its near new / exchange etc , means nothing today 

Lots for you to check & test

Bruce Buchanan
Buchanan Automotive    (40 years working on Porsche sports cars 6 days a week )

[TINGY]

Is it just the solenoid not working properly

I was going to say hit it with a hammer, been there done that before not to Porsche's though, I've seen this happen a few times before.

[944 Geek]

Thanks Bruce for such a thorough list. You certainly know your stuff. What you are describing is exactly what is happening to my car. I also notice this happens when the thermofan is running and I try to start, so I am beginning to suspect a combination of battery and hot starter.

No crank. Even if I apply direct power to the starter motor solenoid trigger wire in the loom teh start solenoid doesn;t activate to turn teh starter motor. I am beginning to suspect the battery

Every Summer ( at work ) we see Porsche's that are more than 10 years old have starter motor ( not cranking ) issues , & the hotter the weather the more we see , 8 out of 10 times is just a starter motor issue , and not just the solenoid , we have had old & not that old Bosch starter motors that will experience Armature & or Field windings/Commutator issues when they are very hot ( not super common ) but we see it 

Common scenario } Hot weather , hot engine , starter motor very much "Heat Soaked"  in that particular Porsche , be it a 911 , 944 , 928 , engine is turned off & then the owner goes to start the engine "say" 5 minutes later & the starter motor does nothing , no cranking & often not even a click ( ZERO ), the owner then lets the car sit for "say " 20 minutes & all of the sudden the engine cranks over because the starter motor wants to work now 

The same car , the same starter motor , same drive time , but this time the ambient temp is 10 degrees cooler , the starter motor is still hot( heat soaked ) but not quite as bad & its just able to cope & all is well 

Two weeks ago we had a new to us customer turned up at our workshop in a 968 , he parked it outside & came in for a chat about the car & as he got in his 968 there was silence , his starter motor did not operate( very Hot day ) , so what we ( Sean & I ) usually do in this situation is to quickly isolate the issue & the quickest way is for us to tap the old stater motor with a small plastic hammer & instantly the old starter motor came to life , so we knew with this car its just a starter motor issue ( Very Very Very Very common ) when starter motors get beyond 10 years of age & thousands of heat cycles 

Other times is a combination of several factors , like } 

A )    Voltage drop to terminal 50 on the starter & this voltage drop is worse when the car in question is hot ( so this has to be checked in this condition )
        Engine cold =   Voltage supply check with a voltmeter at terminal 50
        Engine Hot ( & I mean proper heat soak hot ) = Voltage check at terminal 50 with a voltmeter , often when the car/engine is very hot there will be a" bad enough "voltage drop to terminal 50 on the starter motor 

You do not want voltage drops at Terminal 50 

B )   Poor quality Battery ( if you see the words on the battery ) = Made in Indonesia ,change battery with another as a test , because we have experienced dozens of "made in Indonesia " batteries play up intermittently over the last 2 decades ( at least ) & they all internally disconnect intermittently & then reconnect ( like a loose plate )

Note } The poor quality made in Indonesia battery , is not the fault of the Indonesians , they are just supplying what we have Demanded from them , we have demanded the cheapest ones they / anyone can supply & thats what we get , we get what we pay for ( sounds familiar doesn't it )

Note } we only supply & fit Calcium Batteries to Porsche's , they are all (Brands / Labels) made in South Korea & are fantastic 

C )  If you have the original battery cables & lugs from 1985 then this will always give issues ( I take it that the car is a 1985 ) where the battery is up front , if it is these give a lot of grief with the cable from the battery to there body & from the body to the engine , thats because they are crimped & they go high resistance in old age 

D )  Exchange / Reconditioned  Starter motors & Alternators , have we seen these play up in the first year or two ?  ( hell Yes ) , we had a customer supply a Genuine Bosch Exchange Alternator for his 951( from the USA) just before Xmas & its failed last week  ( Thank GOD we did not supply it )  , you can see we are seeing a bit of this stuff & we stopped supplying this stuff some time ago because of quality controls with Starter motors & Alternators 

F )  We see quite a few failures of the completely different after market "New " starter motors in the last 3 years particularly & again mostly in hot weather 

Just because its near new / exchange etc , means nothing today 

Lots for you to check & test

Bruce Buchanan
Buchanan Automotive    (40 years working on Porsche sports cars 6 days a week )

Thanks Bruce for such a thorough list. You certainly know your stuff. What you are describing is exactly what is happening to my car. I also notice this happens when the thermofan is running and I try to start, so I am beginning to suspect a combination of battery and hot starter.

[Airhead]

, so what we ( Sean & I ) usually do in this situation is to quickly isolate the issue & the quickest way is for us to tap the old stater motor with a small plastic hammer & instantly the old starter motor came to life ,

And that's why you pay big bucks to the experts. They know EXACTLY where to tap the big hammer. 

[944 Geek]

Every Summer ( at work ) we see Porsche's that are more than 10 years old have starter motor ( not cranking ) issues , & the hotter the weather the more we see , 8 out of 10 times is just a starter motor issue , and not just the solenoid , we have had old & not that old Bosch starter motors that will experience Armature & or Field windings/Commutator issues when they are very hot ( not super common ) but we see it 

Common scenario } Hot weather , hot engine , starter motor very much "Heat Soaked"  in that particular Porsche , be it a 911 , 944 , 928 , engine is turned off & then the owner goes to start the engine "say" 5 minutes later & the starter motor does nothing , no cranking & often not even a click ( ZERO ), the owner then lets the car sit for "say " 20 minutes & all of the sudden the engine cranks over because the starter motor wants to work now 

The same car , the same starter motor , same drive time , but this time the ambient temp is 10 degrees cooler , the starter motor is still hot( heat soaked ) but not quite as bad & its just able to cope & all is well 

Two weeks ago we had a new to us customer turned up at our workshop in a 968 , he parked it outside & came in for a chat about the car & as he got in his 968 there was silence , his starter motor did not operate( very Hot day ) , so what we ( Sean & I ) usually do in this situation is to quickly isolate the issue & the quickest way is for us to tap the old stater motor with a small plastic hammer & instantly the old starter motor came to life , so we knew with this car its just a starter motor issue ( Very Very Very Very common ) when starter motors get beyond 10 years of age & thousands of heat cycles 

Other times is a combination of several factors , like } 

A )    Voltage drop to terminal 50 on the starter & this voltage drop is worse when the car in question is hot ( so this has to be checked in this condition )
        Engine cold =   Voltage supply check with a voltmeter at terminal 50
        Engine Hot ( & I mean proper heat soak hot ) = Voltage check at terminal 50 with a voltmeter , often when the car/engine is very hot there will be a" bad enough "voltage drop to terminal 50 on the starter motor 

You do not want voltage drops at Terminal 50 

B )   Poor quality Battery ( if you see the words on the battery ) = Made in Indonesia ,change battery with another as a test , because we have experienced dozens of "made in Indonesia " batteries play up intermittently over the last 2 decades ( at least ) & they all internally disconnect intermittently & then reconnect ( like a loose plate )

Note } The poor quality made in Indonesia battery , is not the fault of the Indonesians , they are just supplying what we have Demanded from them , we have demanded the cheapest ones they / anyone can supply & thats what we get , we get what we pay for ( sounds familiar doesn't it )

Note } we only supply & fit Calcium Batteries to Porsche's , they are all (Brands / Labels) made in South Korea & are fantastic 

C )  If you have the original battery cables & lugs from 1985 then this will always give issues ( I take it that the car is a 1985 ) where the battery is up front , if it is these give a lot of grief with the cable from the battery to there body & from the body to the engine , thats because they are crimped & they go high resistance in old age 

D )  Exchange / Reconditioned  Starter motors & Alternators , have we seen these play up in the first year or two ?  ( hell Yes ) , we had a customer supply a Genuine Bosch Exchange Alternator for his 951( from the USA) just before Xmas & its failed last week  ( Thank GOD we did not supply it )  , you can see we are seeing a bit of this stuff & we stopped supplying this stuff some time ago because of quality controls with Starter motors & Alternators 

F )  We see quite a few failures of the completely different after market "New " starter motors in the last 3 years particularly & again mostly in hot weather 

Just because its near new / exchange etc , means nothing today 

Lots for you to check & test

Bruce Buchanan
Buchanan Automotive    (40 years working on Porsche sports cars 6 days a week )

Bruce you nailed it. I fabbed a nice heat shield from aluminium and no more problem... Why didn't Porsche think of this?

[firstone]

Zjermans are no better engineers than any other. Sometimes worse. After all, we're just monkeys in shoes.

[944 Geek]

Yes funny about that.  I love the wiring where if your hazard light fuse blows you lose brake lights even though the brake light fuse is intact...

They were really trying to save money in the '80s.

[Buchanan Automotive]

Bruce you nailed it. I fabbed a nice heat shield from aluminium and no more problem... Why didn't Porsche think of this?

Actually I wasn't even thinking of a heat shield , the 2.5L NA 944 starter motor in good condition can cope easily without a heat shield ( they never needed one ), thats what I meant  , or put another way the starter motor has an issue if it helps it now , and yes you may find that a heat shield may help , but the issue will return as the issue worsens with time

Remember most( I mean 60% + ) of the heat is just transferred through the alloy body of the starter motor via the bell housing / engine its bolted up to 

If you find a heat shield does help , then you may have isolated the issue to some degree , meaning if true then the stater-motor is more likely to be the issue

The next time it happens & there is a 90% chance it will , maybe not the remainder of this summer , but a stinking hot day next year , while its in the "not cranking mode" , use a jump wire from the battery 12V + directly to terminal 50 ( yellow switching terminal ) on the starter solenoid , if it cranks then you know you have a voltage drop "When Hot " as well as a starter motor problem , it all comes down to diagnoses

Remember as old cars get older ,strange electrical things will happen, hence why we often rewire different old systems( be it starter wiring looms or alternator wiring looms or engine management wiring looms )on 1970's & 1980's Porsche's at work all the time to stop things like this from happening 

Regards

Bruce Buchanan

Buchanan Automotive