Engine Heat Soak - What causes sluggishness

[ryan2022]

Hi guys,

Other than the air temp going into the intake, what causes the vehicle to become sluggish once its fully warmed up on a hot day?

I'm thinking it's just the temp, throttle body temp etc....effecting the air entereing the engine. I don't see a reason why a warm block and a slightly higher engine temp itself should change anything....I'm not an expert in thermodynamics though.

 

[Colt45ws]

Hotter intake air is less dense and also it has to retard timing due to the heat.
Here is what the retard for air temperature looks like on my car in the PCM.
Code:


254F -74

160F -74

120F -30

100F 0

60F 4

-256F 10

-256F 10

I know Ive idled with the A/C on and seen towards 140F intake temperature, so its pulling crazy amounts of timing. 40-50 degrees?

 

[LoneRanger]

How are you able to see that, are you data logging ?

 

[Colt45ws]

Originally Posted By: LoneRanger
How are you able to see that, are you data logging ?


I have SCT Pro Racer package so I can view and edit the program as I see fit.

 

[ryan2022]

Wo, that's pretty cool! I completely forgot about the timing retarding. That makes sense. It's amazing how much it does it given those temps listed. That's wild.

I was thinking about it on my way home. Pretty cool.

I wonder if using synthetic with supposed better heat transfer could actually keep the timing slightly closer to spec.....The differences would be very small I'm sure.

I've heard differences of opinion on synthetic vs conventional for heat transfer, so this is assuming a lot. Maybe just one vs/ the other.

 

[Ramblejam]

Knock retard.

 

[Colt45ws]

Since its coming from the Air temp sensor, the oil in the sump isn't going to make much difference.
Newer high performance vehicles that monitor oil temperature may have a derate on that as well. But, it would be at the extreme to keep the engine from melting.
About the only thing you can do is plumb the intake air to a cooler location.


I find after a few minutes of driving the Air temp has dropped to near ambient and the power comes back, as expected. So I don't worry about it too much.

Oh, also, the maximum timing it can have at idle is 50 degrees and the minimum it can ever command is -10, so it will never see the full 74 degrees of retard in the table.

 

[ryan2022]

Thanks Colt, that's some interesting stuff. I always wondered. It's most noticeable in traffic, and you're right. Once you're on the road it cools off and picks back up.

 

[KingCake]

If you actually notice power loss from normal driving than something is wrong outside of normal heat soak.

 

[ryan2022]

Well, the truck isn't a rocket regardless, but only notice it mildly when its hot out, and I've been stuck in traffic for an hour....once the air is flowing around the engine compartment again its fine. It might be in my head.

 

[jigen]

Eh, I always feel like I notice it. Regardless of the vehicle really.

65 degree driving and 95 degree driving when it's very humid out... I always felt a difference. But hey, it could all be in my head.

 

[splinter]

A general rule of thumb is that engine output changes ~1% per ~11°F IAT difference. Witness SAE correction factors and DA calculations at the airport.

We're in a tsunami zone along the coast in a mild clime but can feel the change of response and grunt with ambient temperature variation through the seasons.

Our supercharged AMG has typical self-preservation strategies programed into its ECU contingent upon, among other factors, IAT.
Thrust takes a big hit when things get toasty!

 

[aquariuscsm]

My car must be a beast of a different kind,because I have the most power,smoothness,and responsiveness when the engine is piping hot on the hottest summer day.

 

[Fsharp]

Originally Posted By: ryan2022
Well, the truck isn't a rocket regardless, but only notice it mildly when its hot out, and I've been stuck in traffic for an hour....once the air is flowing around the engine compartment again its fine. It might be in my head.


Besides retarded ignition timing, the sluggishness you describe could also be from the fan clutch engaging when it's hot or you're in traffic. That'll put a noticeable load on a 4 cylinder like your Ranger.

 

[donnyj08]

Originally Posted By: jigen
Eh, I always feel like I notice it. Regardless of the vehicle really.

65 degree driving and 95 degree driving when it's very humid out... I always felt a difference. But hey, it could all be in my head.


I can tell as well. Combine the high heat of summer and A/C running and my Silverado feels sluggish compared to a cool 60 degree day with the windows down.

 

[UncleDave]

On top of the aforementioned loss of fuel air destiny to heat combined with litany of parasitic loads - if you add a few thousand feet of altitude along with the above results are simply dazzling.

The amount of performance that slices off a naturally aspirated engine is significant.


UD

 

[Pontual]

Maybe a piston soak to clea the tops, ir running premium to experiment, if there is carbon pulli g iyt timing.