Question about heat in engine bay

[James Morse]

About the '97. When I opened the hood after driving some, I noticed today that it seemed really hot under there. But the truck doesn't run hot. It never gets past the middle of the gauge. It seems to work because it goes all the way cold and running, you see it coming up to mid-range then stays there, maybe tiny variations, but it's stable. Lot of coolant. The fact it doesn't run hot doesn't make me suspect things like fan (it works, pulls lots of air through the rad) or water pump (can't see it working, but if it weren't, I think the engine would go very very hot in short time). Or t-stat. Any of those things bad would cause it to run super hot afaik.
My thinking: Engine is supposed to run something like 180F, right? That means radiator has to bleed off heat, obviously, that's what it's for. Where does that heat go? It blows over the engine and a lot of it (heat) probably stays in the engine bay. Like, you're cooling, but then blowing that over the engine. Anyway, engine runs fine, no odd noises, lots of power, which kind of leaves me with, there's nothing wrong, at least nothing I can think of.
So my question is, if you drive on a warm day (let's say 75F or up and sunny), how hot should it be under the hood? To me it seemed really hot, but maybe that's normal. My guess is, it shouldn't be over about 180F, and if that's true, then I guess that's not so hot to wreck components or melt plastic, but I have to say, it just seemed super hot. I didn't measure the temp, if I see it like that again (likely) I will. I started it in the driveway and ran a/c and let it run a while but it didn't get real hot in the bay, that's just not the same test really because before I was driving a while then stopped at a quick mart, left it running, drove the 1/2 mile home, that's when I checked it because it actually kind of smelled hot if you know what I mean.
Maybe it is a non-issue. I just don't remember other vehicles being this super hot in the bay when you open the hood, and it seems like I would have noticed it... maybe not.

 

[85_Ranger4x4]

Engine coolant will run 190-200*

You also have exhaust under there though..

It will get pretty warm under there.

 

[James Morse]

OK. Thanks. Sounds like you're saying I shouldn't worry about it, just the nature of the beast.

 

[Roert42]

$10 ford lightning guy tells you to drill holes in your hood and attach a scoop over top.


The hot air gets pulled down under the truck while you’re driving. The engine bay will get a lot hotter while stopped vs driving.

 

[James Morse]

Um. No. On cutting the hood.
Yes it would have to exhaust the hot air under the truck, no where else for it to go. Then if you're sitting there - yeah - I get it. Thanks.
Some cars have rad exhaust air coming up thru the hood forward of the engine, I think that would way reduce heat in the bay. But they are set up for it.
For instance this; you see the big cutout in the hood.

 

[MISWFL]

My 1st gen CRX's have a temp sensor in the engine compartment that turns on the radiator cooling fan if the under hood temp gets too high.

 

[James Morse]

What's the temp when it cuts in?

 

[MISWFL]

I don't remember. It's in the factory service manual, but I don't have it or the car anywhere near me.

It would also turn on and run after the key was off. It's to avoid heat soak because it's carbureted. All the 1984-1987 carbureted Civics have it and probably most of the Hondas of that era.

 

[James Morse]

That's pretty cool.
I don't know what heat soak is, but seems to me on the old carb engines you could run into no-hot-start issues, open the throttle plate and pour in gas... something like that. It's been a while.
Not sure if that's what you're talking about. I might just be describing a faulty carb there.
Edit: come to think of it, Saabs, the fan would run after it was shut off, if hot. Must be same idea, though they were efi.

 

[RonD]

Actually the Ford thermostats are 190-195degF after 1975 or so
205 is 1/2 on dash temp gauge, so just below 1/2 is normal operating temp

If temp goes up at idle then fan clutch is bad
If it goes up while driving then thermostat or water pump usually, but can be old radiator, clogged passages

If the sun is out the hood gets very hot on its own, the darker the color the hotter it gets, but insulation on underside of hood keeps engine bay cooler, also keeps engine heat from getting the underside of hood too hot
Most of the heat in engine bay comes from exhaust manifolds, they run at minimum 800degF to 1,000degF, some times even hotter
O2 sensors don't even work under 650degF

So yes it can/does get hot in engine bay but normal, 250-300degF on an 80+degF day

 

[MISWFL]

Yes, heat soak is when the hot engine makes the engine compartment get hotter after shutdown, due to no air flow. The idea of the fan running a few minutes is to keep the fuel in the carb bowl from boiling and evaporating, making it harder to start again.

 

[James Morse]

Thanks Ron, wow, that's really hot at 250-300 but the components must be rated to not degrade/melt at those temps.
Mine stays just below 1/2 like you say, doesn't seem to matter idling, running, whatever. Like I said, small variations, but, never goes hot.

 

[lil_Blue_Ford]

It gets hot enough to cook food, old trick was to wrap your lunch in foil and set it on top of a hot engine…

 

[sgtsandman]

The coolant temperature doesn’t reflect the temperature in the engine bay. As stated, the temperatures of the exhaust and other things is going to be higher than the engine temperature is going to be.

Usually, the engine bay temperatures are not going to be an issue as long as the cooling system is doing it’s job. Between the fan and the forward motion of the vehicle, the hot air is going to get pushed out under the vehicle.

One situation where engine bay temperatures CAN be an issue is off road driving, where the engine is working hard and the vehicle is moving slowly.

Usually, as long as the grill area is unobstructed and the radiator isn’t clogged up with leaves, brush, and sticks, it still isn’t a problem.

 

[19Walt93]

Heat soak is more of a problem for carbureted vehicles now that our gas is polluted with alcohol because it vaporizes faster when hot and doesn't vaporize for crap when sub zero. There are still different blends of gas for winter and summer. I always run a 1 inch, 4 hole phenolic carb spacer to keep the heat away from the fuel as much as possible. I've seen hoods spaced up and inch or so in the rear to let heat out, the problem is that heat will then be drawn in through the cowl vent and into the cab. "Hot" and "cold" are relative, I feel hot at 80 degrees, my engine thinks it's cold below 180 or 190 and tolerates 210.