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Old 01-05-2009, 10:01 PM   #1
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Default So my car won't start once the engine is hot, help!

In the mornings and after work, when the engine is cold, the car will start just fine but if I drive around for a little and turn it off, it won't start unless I press the gas all the way in. What can be wrong? We recently changed the spark plugs, oil, radiator fluid and fuel filter. It didn't do any of this before, so I'm guessing something we did made it bad. The car runs fine once it's on, so I don't think it's the spark plugs...the car is a 98 camaro z28.

Also, the engine light came on and the mechanic said it had to do something with the air/cooling system since it made the fans stay on after the car was off, even if it was cold. I just want to see if it's something that's easy to fix before I take the car to the mechanic.
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Old 01-05-2009, 10:05 PM   #2
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Usually when the fans stay on after the engine is shut off is because its really hot. Maybe your temp guage isn;'t reading right and its actually real hot. You may have an overheating issue.

Also, a hot engine is harder to start than a cool engine, so you might be actually HOT!!! So it would be normal to have a hard start when hot.

Open the radiator cap when the engine is cold, make sure its full, you could have air in the system and not have it topped off and its getting hot.

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Old 01-05-2009, 10:18 PM   #3
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Usually when the fans stay on after the engine is shut off is because its really hot. Maybe your temp guage isn;'t reading right and its actually real hot. You may have an overheating issue.

Also, a hot engine is harder to start than a cool engine, so you might be actually HOT!!! So it would be normal to have a hard start when hot.

Open the radiator cap when the engine is cold, make sure its full, you could have air in the system and not have it topped off and its getting hot.
I checked it, it's full. We just flushed it and replaced it with coolant and topped it off. Maybe the coolant sensor is not right?
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Old 01-05-2009, 10:28 PM   #4
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I checked it, it's full. We just flushed it and replaced it with coolant and topped it off. Maybe the coolant sensor is not right?
If you're sure there's no air bubble in there, the sensor could be the culprit. Next time you drive it and you turn the engine off and the fans are still running.....pop the hood and see if its hotter than normal. You should be able to keep your hand on the intake.
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Old 01-05-2009, 10:41 PM   #5
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If you're sure there's no air bubble in there, the sensor could be the culprit. Next time you drive it and you turn the engine off and the fans are still running.....pop the hood and see if its hotter than normal. You should be able to keep your hand on the intake.
Yeah, I'm pretty sure. How hard would it be to change the sensor?
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Old 01-05-2009, 11:00 PM   #6
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Yeah, I'm pretty sure. How hard would it be to change the sensor?
about 2 minutes. unplug it and take it out. Its brass so start to crank it out slowly and hope it doesn't shear off. Mine did. I had to take a sharp phillips screwdriver head and tap it into it with a hammer, then turned it out with a ratchet. Just in case that happens to yours.

Put it in just snug because I broke mine putting it back in, too tight it will shear off. It does not have to be seriously tight. Snug, then another half turn.

the dealer or www.rockauto.com should have them in stock.
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Old 01-05-2009, 11:10 PM   #7
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about 2 minutes. unplug it and take it out. Its brass so start to crank it out slowly and hope it doesn't shear off. Mine did. I had to take a sharp phillips screwdriver head and tap it into it with a hammer, then turned it out with a ratchet. Just in case that happens to yours.

Put it in just snug because I broke mine putting it back in, too tight it will shear off. It does not have to be seriously tight. Snug, then another half turn.

the dealer or www.rockauto.com should have them in stock.

Can you tell me where exactly is the coolant sensor? I'm not too familiar with the LS1.
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Old 01-05-2009, 11:23 PM   #8
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Can you tell me where exactly is the coolant sensor? I'm not too familiar with the LS1.
If you look at the forward spark plug on the drivers side head, you will see a plug that plugs into the head just above that spark plug. Thats it.
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Old 01-05-2009, 11:32 PM   #9
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If you look at the forward spark plug on the drivers side head, you will see a plug that plugs into the head just above that spark plug. Thats it.
Thanks! Hopefully replacing it will solve this problem.
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Old 01-05-2009, 11:33 PM   #10
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Cool, good luck.
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Old 01-05-2009, 11:48 PM   #11
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yikes,hmmm let us know how that sensor worked for ya,mabe that cam positioning sensor or throttle positioning sensor,when my fuel pump was going out it did that,got hot wouldnt start but i dont know,good luck
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Old 01-06-2009, 12:00 AM   #12
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Only thing "carwatcher", before you go buying parts: If the engine is hard to start when its hotter, it can be a few things. A bad battery, a dying alternator that isn't charging the battery all the way, a million different heating issues making the engine hot which in turn will even make a perfectly good battery have a hard start when the engine is hot.

The bad sensor can just make the fans come on when they are not supposed to and NOT work when they are supposed to and a few other things. But it can't make you have a hard start.

I would first make sure you are really NOT getting hot. If you're NOT really getting hot, then you need to find out why its hard to start, and thats most likely NOT the temp sensor.

The sensor could be disabling your fans during city driving and maybe thats why you're getting hot.

Holy ****, I'm starting to confuse myself.


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Old 01-06-2009, 12:04 PM   #13
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In the mornings and after work, when the engine is cold, the car will start just fine but if I drive around for a little and turn it off, it won't start unless I press the gas all the way in. What can be wrong? We recently changed the spark plugs, oil, radiator fluid and fuel filter. It didn't do any of this before, so I'm guessing something we did made it bad. The car runs fine once it's on, so I don't think it's the spark plugs...the car is a 98 camaro z28.

Also, the engine light came on and the mechanic said it had to do something with the air/cooling system since it made the fans stay on after the car was off, even if it was cold. I just want to see if it's something that's easy to fix before I take the car to the mechanic.

I doubt it's your overheating issue causing this. Flooring the gas pedal while cranking cuts the fuel from your injectors incase the engine floods. I believe you have some leaky injectors flooding your cylinders. You don't get it when it's cold because the fuel has enough time to evaporate off.

Put a fuel pressure gauge on your rails and see if it bleeds off a little from the injectors leaking.

Also with the heat issue you may want to make sure your thermostat is opening and closing at the right temps.
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Old 01-06-2009, 12:51 PM   #14
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I doubt it's your overheating issue causing this. Flooring the gas pedal while cranking cuts the fuel from your injectors incase the engine floods. I believe you have some leaky injectors flooding your cylinders. You don't get it when it's cold because the fuel has enough time to evaporate off.

Put a fuel pressure gauge on your rails and see if it bleeds off a little from the injectors leaking.

Also with the heat issue you may want to make sure your thermostat is opening and closing at the right temps.
But if the engine really IS NOT running hot, and the fans stay on after the engine is turned off....thats most likely a bad temp sensor.

If the engine really IS running hot it may be because the sensor is also not turning them on when they are needed in city driving, and making it hot.

Bottom line though.....a hard start when the engine is warm/hot/very hot...whatever, as opposed to a nice strong start when cold.....leads to a weak battery.

Why is it weak? Bad battery or failing alternator?

Looks like that sensor must be changed to rule it out. If its bad, the fan issue will be fixed. check the battery/alternator to make sure they are fine.
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Old 01-06-2009, 02:05 PM   #15
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leaky injector
fuel pump going out
could have a loose or damaged battery cable.
loose or damaged stud on the starter.
i dont think the coolant sensor is your problem, IMO.
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Old 01-06-2009, 02:25 PM   #16
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leaky injector
fuel pump going out
could have a loose or damaged battery cable.
loose or damaged stud on the starter.
i dont think the coolant sensor is your problem, IMO.
But none of that causes the fans to run after the engine is turned off.
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Old 01-06-2009, 03:10 PM   #17
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But none of that causes the fans to run after the engine is turned off.
true. the coolant sensor could have an effect on the fans, but i dont see the coolant sensor broken, or corroded would cause problems with hot starting, unless the car was overheating to begin with. then that solves everything.
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Old 01-06-2009, 03:36 PM   #18
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true. the coolant sensor could have an effect on the fans, but i dont see the coolant sensor broken, or corroded would cause problems with hot starting, unless the car was overheating to begin with. then that solves everything.
Thats what I was saying. 2 problems. One of them fixes both, the other only fixes itself.
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Old 01-06-2009, 04:08 PM   #19
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But if the engine really IS NOT running hot, and the fans stay on after the engine is turned off....thats most likely a bad temp sensor.

If the engine really IS running hot it may be because the sensor is also not turning them on when they are needed in city driving, and making it hot.

Bottom line though.....a hard start when the engine is warm/hot/very hot...whatever, as opposed to a nice strong start when cold.....leads to a weak battery.

Why is it weak? Bad battery or failing alternator?

Looks like that sensor must be changed to rule it out. If its bad, the fan issue will be fixed. check the battery/alternator to make sure they are fine.
I checked today and actually the temperature switch was faulty, not the coolant sensor, it had literally melted off, I barely touched it and it came off, leaving the wires exposed. So I guess that's why the fans were staying on even though the car was cold(I left my hand on the engine and it was not hot at all, after driving 20 miles). And I drove the car with the switch unplugged and it started right up when it was hot, so I guess I found my problem. I also just put in a new battery, so I doubt that was causing it. Now I have to wait until tomorrow for the new temperature switch to arrive.
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Old 01-06-2009, 04:12 PM   #20
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I checked today and actually the temperature switch was faulty, not the coolant sensor, it had literally melted off, I barely touched it and it came off, leaving the wires exposed. So I guess that's why the fans were staying on even though the car was cold(I left my hand on the engine and it was not hot at all, after driving 20 miles). And I drove the car with the switch unplugged and it started right up when it was hot, so I guess I found my problem. I also just put in a new battery, so I doubt that was causing it. Now I have to wait until tomorrow for the new temperature switch to arrive.
Thats wierd. Don't know why you had hard starts though. A bad temp switch or bad temp sensor can't do that. I don;t think it can anyway?

Where is the temp switch you're talking about?
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Old 01-06-2009, 04:12 PM
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