engine turns over real slow when hot

[jfm1]

Hi all, a buddy of mine has a 4cyl. merc. the motor runs great but won't start when hot it turns over real slow. put on a new starter, new sol, battery cables,new battery,checked all grounds still you must wait untill it cools down before it will start. also checked timing, any help with this would be great thanks.

 

[searay3]

Re: engine turns over real slow when hot

Can you give a model/serial so we know what ignition you have. Points or electronic, do an ign tuneup. Always gotta rule out an ignition problem (arcing cap) but since it runs good when cold that probably could be ruled out. Sounds like you did a lot to the starter circuit. With age that was probably a wise decision and didn't hurt other than a few bucks. You could pull the drive and maybe isolate it to the motor or the drive. Is the starter making a grinding or binding noise. Maybe is binding and needs shimmed. A couple of ideas to check....

 

[bruceb58]

Re: engine turns over real slow when hot

Measure the voltage between the negative battery terminal and the starter positive terminal while you are cranking.

Then measure the voltage across the battery while cranking.

Let us know what you get.

 

[xtraham]

Re: engine turns over real slow when hot

timming, or manifold/riser leaking water in the combustion chamber.......

 

[Haut Medoc]

Re: engine turns over real slow when hot

What xtraham said.....
Timing too advanced?
Water leaking into cylinder(s) & seeping past rings when cooled down?
Is there any evidence of water in oil?
Pull the plugs & inspect for signs of water intrusion....
Post serial #, year if possible.....JK

 

[Boatist]

Re: engine turns over real slow when hot

I also agree timing to far advanced. Easy way to tell is to pull the coil wire from the distributer and ground it to the block when hot. If it turns over Normal timing is too far advanced. When hot the plug fires before the piston reaches top dead center and the motor tries to turn backwords against the starter. When cold the combustion is not as fast and allows the piston to reach Top dead center before the presure builds up.

If it turns normal with the coil wire grounded then Take a timing light but have some one loosen the distributer put the coil wire back in and retard timing a little at a time until it starts normal. Tighten it down. Check with your timing light. I also seen some that misread the timming marks.

Check You advance springs they could be streached and when hot not have enough strength to pull the centrifical weights back. Make sure weight move freely and are not rusted and hard to move.

 

[bruceb58]

Re: engine turns over real slow when hot

Please explain why everybody thinks it is timing when the boat cranks properly when cold.

 

[xtraham]

Re: engine turns over real slow when hot

Please explain why everybody thinks it is timing when the boat cranks properly when cold.

pre ignition is much more pronounced at higher engine temps, I think it's the manifolds personaly but it's easier to check the timming before pulling the manifolds..
now can you explain to me why it would crank okay cold with dirty or bad battery cables

 

[bruceb58]

Re: engine turns over real slow when hot

A hot starter can draw a lot more current than a cold starter, especially one that is on its last legs.

 

[xtraham]

Re: engine turns over real slow when hot

A hot starter can draw a lot more current than a cold starter, especially one that is on its last legs.

agree, missinterpted your post, as thinking cables

 

[bruceb58]

Re: engine turns over real slow when hot

I just re-read his post and he said he put in a new starter so who knows.

I just wanted him to measure some voltage drops since that is the easiest thing to do.

 

[Boatist]

Re: engine turns over real slow when hot

The reason I think it is the timing is because both my 4 cylinder 3.0L OMC motor does it and My Chev truck will do the same exact thing when hot after a long tow.

My 57 Chev also did the same thing. All did the exact same thing when hot but would start normal when cold. If I retarded the timing by 2 degrees would start normal all the time.

When it is doing it with the motor hot and oil flowing pulling the distributer coil wire and the motor will spin great.
I just seen this on too many cars and boats.

 

[dmarkvid2]

Re: engine turns over real slow when hot

What kind of car you got pictures Xtraham?

 

[xtraham]

Re: engine turns over real slow when hot

What kind of car you got pictures Xtraham?

1976 Camero, 427cid .060 over 4 speed trans 4:88 rear