Skip the auto shop - Our mechanics make house calls

Q: Car won't start when it is warm.

asked by on

Once my Saturn gets warm and I turn it off I can't get it to restart again till it cools off. When i turn the key it does not do anything it makes no noise. However the head lights do come on. When it is running it drives great, no problems at all. Thanks for any help.

My car has 170348 miles.
My car has an automatic transmission.

This is a common sign of a faulty ignition coil. Ignition coils are coated with a varnish-like insulation that becomes brittle over time after being stretched then contracted repeated as the copper beneath them expands and contracts at a higher coefficient than the insulation. The insulation develops micro fractures that open when heated and close when cooled. When open, they allow shorting of coil windings and decrease or eliminate the coil’s ability to function. This type of temperature cycling happens because every time you shut the engine off, the fan stops running, the coolant stops flowing and the temperature under the hood rises.

Every time you start the engine again the coolant flows, the fans turn on, and the temperature drops. The areas in and around the tops of the combustion chambers, the exhaust manifolds, and the exhaust components are hundreds of degrees hotter than the outside temperature under the hood. When this heat dissipates and is absorbed under the hood, it is trapped causing this cycling effect. Components that contain heat sensitive materials include parts like coils, injectors, igniters, and some sensors. Any of these may be potentially subject to this same kind of heat problem which can be very difficult to trace. I would recommend having an expert from YourMechanic come to your location to take a look at your truck to properly diagnose your ignition system.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Vehicle not moving when transmission is in drive

A vehicle not moving when put into, drive can be caused by many things. The problem may be as simple as the need to add some transmission fluid to as serious as the need for a replacement transmission. As the...

Q: Have oil on one of my spark plug wires in the spark plug well the test are fine. What should I do.

Hi there. The issue that you are having is a small o-ring seal on your valve cover is either split or damaged. The valve cover should have a seal all the way around it and 4 o-rings in the middle...

Q: Coolant leaked out of coolant reservoir

Leaks normally will leave a white residue or wet spot at the leak source. If the leak is not obvious a cooling system pressure test may be necessary to determine if there is a leak present. Another possibility could be...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.