300E engine dies on hot days

[m pautz]

I have a 300E that will run all day long as long as it is moving. On a
hot day with the airconditioner running, it will die withing about 5 min
if sitting in a fast food line (half-fast). If there is a traffic delay
where the car is sitting idling for about 5 min, it dies. The aux fan
comes on and the temperatur gage indicates normal temp.

The car will crank, but will not start. Sometimes it *might* sputter,
but that is about it. If I open the hood and let it sit for 10-30
minutes, it will start just fine and run all day long again (until stuck
in traffic)

I have confirmed and can duplicate the problem. I can drive around, come
back home, and let it sit in the street idling. After just a short
while it will die every time. It will not start until it has cooled.
So, if I try a 'supposed' fix, I can verify if it is truly a fix or not.

Any thoughts?

[Tiger]

I would try the fuel filter first... then fuel pump relay.

[T.G. Lambach]

Your description sounds like a classic vapor lock but could also be due
to a heat related failure of an electrical component. If the fuel system
pressure is below specification the fuel will be prone to vaporize in
the condition that you describe. An intermittent electrical component
can be a devil to find - often a "let's try this and if it doesn't fix
it we'll try that" approach - all with your money. Something like the
ignition coil, for instance.

[m pautz]

Post by T.G. Lambach
Your description sounds like a classic vapor lock but could also be due
to a heat related failure of an electrical component. If the fuel system
pressure is below specification the fuel will be prone to vaporize in
the condition that you describe. An intermittent electrical component
can be a devil to find - often a "let's try this and if it doesn't fix
it we'll try that" approach - all with your money. Something like the
ignition coil, for instance.

The intermittent electrical possibility was my first thought; especially
in this day of semiconductor ignition. I had thought about a vapor
lock, but then why did it start happening and also happening with
consistancy.

I was concerned about the "let's try this" type of solution. That is
why I tried to see if I could duplicate the problem every time. If
something is changed, it is very quick to discover if the change was the
solution.

[T.G. Lambach]

Sounds silly - but you cold try an ice pack on selected electrical
components and see when the engine continues running. I'd start with the
coil.

[Rugbyguy]

When the engine bay heats up (from slow driving, idling, hot weather), a
failing/failed ignition coil will abruptly and consistently stop providing
spark until it cools down. Once cooled, the car again starts and runs,
until the engine bay gets hot again. The buildup of engine bay heat from
the engine itself, the hot weather, the slow driving usually makes a bad
coil react that way, failing when hot, working again when cooled.

Try changing out the ignition coil.

Post by m pautz
I have a 300E that will run all day long as long as it is moving. On a
hot day with the airconditioner running, it will die withing about 5 min
if sitting in a fast food line (half-fast). If there is a traffic delay
where the car is sitting idling for about 5 min, it dies. The aux fan
comes on and the temperatur gage indicates normal temp.
The car will crank, but will not start. Sometimes it *might* sputter,
but that is about it. If I open the hood and let it sit for 10-30
minutes, it will start just fine and run all day long again (until stuck
in traffic)
I have confirmed and can duplicate the problem. I can drive around, come
back home, and let it sit in the street idling. After just a short
while it will die every time. It will not start until it has cooled.
So, if I try a 'supposed' fix, I can verify if it is truly a fix or not.
Any thoughts?

[Tiger]

Mmm... never thought about that... sounds very plausible.

[m pautz]

I figured the same thing about the heat buildup inside the engine
compartment. However, my first thought was something electonic
(semiconductor). The Ignition coil is nothing more than a high voltage
transformer. I can't think of how heat would make it fail. The heat can
not affect the windings, and I can't think how the heat will affect the
magnetic flux of the core. Have you, or anyone else, had experience with
this. I would hate to pay ~$100 if it isn't the cause.

Post by Rugbyguy
When the engine bay heats up (from slow driving, idling, hot weather), a
failing/failed ignition coil will abruptly and consistently stop providing
spark until it cools down. Once cooled, the car again starts and runs,
until the engine bay gets hot again. The buildup of engine bay heat from
the engine itself, the hot weather, the slow driving usually makes a bad
coil react that way, failing when hot, working again when cooled.
Try changing out the ignition coil.

Post by m pautz
I have a 300E that will run all day long as long as it is moving. On a
hot day with the airconditioner running, it will die withing about 5 min
if sitting in a fast food line (half-fast). If there is a traffic delay
where the car is sitting idling for about 5 min, it dies. The aux fan
comes on and the temperatur gage indicates normal temp.
The car will crank, but will not start. Sometimes it *might* sputter,
but that is about it. If I open the hood and let it sit for 10-30
minutes, it will start just fine and run all day long again (until stuck
in traffic)
I have confirmed and can duplicate the problem. I can drive around, come
back home, and let it sit in the street idling. After just a short
while it will die every time. It will not start until it has cooled.
So, if I try a 'supposed' fix, I can verify if it is truly a fix or not.
Any thoughts?

[Rugbyguy]

Because it pushed me to the edge of sanity in a 1969 280S that kept stalling
in heavy traffic, midway in intersections, on creeping freeway commutes,
during hot days, with the A/C on and the engine bay building up heat. It
also happened the same way on an outboard engine on a powerboat I owned;
after a hard power run, then stopping to an idle, the engine would die in
five minutes as if the ignition had been shut off. It would not start for
20 to 30 minutes until the coil had cooled down. It was consistently,
repeatably, reliably failing the same way every time.

In both cases, in my 280S and in my power boat, the problem was resolved
with a new ignition coil.

Post by m pautz
I figured the same thing about the heat buildup inside the engine
compartment. However, my first thought was something electonic
(semiconductor). The Ignition coil is nothing more than a high voltage
transformer. I can't think of how heat would make it fail. The heat can
not affect the windings, and I can't think how the heat will affect the
magnetic flux of the core. Have you, or anyone else, had experience with
this. I would hate to pay ~$100 if it isn't the cause.

Post by Rugbyguy
When the engine bay heats up (from slow driving, idling, hot weather), a
failing/failed ignition coil will abruptly and consistently stop providing
spark until it cools down. Once cooled, the car again starts and runs,
until the engine bay gets hot again. The buildup of engine bay heat from
the engine itself, the hot weather, the slow driving usually makes a bad
coil react that way, failing when hot, working again when cooled.
Try changing out the ignition coil.

Post by m pautz
I have a 300E that will run all day long as long as it is moving. On a
hot day with the airconditioner running, it will die withing about 5 min
if sitting in a fast food line (half-fast). If there is a traffic delay
where the car is sitting idling for about 5 min, it dies. The aux fan
comes on and the temperatur gage indicates normal temp.
The car will crank, but will not start. Sometimes it *might* sputter,
but that is about it. If I open the hood and let it sit for 10-30
minutes, it will start just fine and run all day long again (until stuck
in traffic)
I have confirmed and can duplicate the problem. I can drive around, come
back home, and let it sit in the street idling. After just a short
while it will die every time. It will not start until it has cooled.
So, if I try a 'supposed' fix, I can verify if it is truly a fix or not.
Any thoughts?

[Lumpy]

Hmm well I had a similar overheating problem in my 1991 300E, would
happen on hot days or heavy traffic. After checking the electrics, my
mechanic replaced the black box under the hood with another spare (they
are VERY expensive). That didn't solve the problem -- it was the wiring
harness attached to it that was intermittent -- replacing it worked.

Afterwards we also found out that one of the engine fans had been
incorrectly wired and was spinning in reverse, not cooling the engine
at all.

[m pautz]

Post by Lumpy
Hmm well I had a similar overheating problem in my 1991 300E, would
happen on hot days or heavy traffic. After checking the electrics, my
mechanic replaced the black box under the hood with another spare (they
are VERY expensive). That didn't solve the problem -- it was the wiring
harness attached to it that was intermittent -- replacing it worked.

That must have been a bad connector. Wires don't go bad unless broken or
the insulation is damaged.

Post by Lumpy
Afterwards we also found out that one of the engine fans had been
incorrectly wired and was spinning in reverse, not cooling the engine
at all.

My engine is not overheating. The temp gage is in the normal area. The
problem is heat buildup in the engine compartment that is causing some
component to overheat.

[jackfortunati]

Hello, my car has same issue. It loses spark. I think the contacts and rotor button inside the dostributor are a possible cause, or the crank pulley sensor, cooling them with an electric leaf blower allows the car to have spark again and run.

I also suspect the exhaust manifolds and converters are overheating the engine bay, I think to put mineral wool insulation over the manifold side of then engine to contain heat and displace it downstream

[the other Donald]

Hello, my car has same issue. It loses spark.  I think the contacts and
rotor button inside the dostributor are a possible cause, or the crank
pulley sensor, cooling them with an electric leaf blower allows the car
to have spark again and run.
I also suspect the exhaust manifolds and converters are overheating the
engine bay, I think to put mineral wool insulation over the manifold
side of then engine to contain heat and displace it downstream.

I'm usually too drunk to get behind the wheel of an auto
--
-
-Donald in Austin
AA #2104
Apatriot #22
Atheist FF/EMT
....and ordained minister
Stork pin recipient: May 1, 2003 -Madelyn

-Mr. Worf, set phasers on "Fuck You" and fire at will. -Doc Smartass