Average temp ranges?

[CyborgGold]

I am working on a project and I am having difficulty finding the average high and low operating temperatures at various points of an engine. My project is focusing on 4-cyl engines at the moment, and the points of interest are the block, headers, and exhaust. I am also interested in any other high heat areas of the engine any of you can come up with. I am interested in the temperatures you could come into contact with by just opening the hood/lifting the vehicle. Thanks in advance!!

[shorod]

I don't have a 4-cylinder in my garage currently, but I could get you a thermal image of under the hood after a drive which might help you understand what temps a person could be exposed to just by opening the hood or lifting a vehicle. The software for my thermal imaging camera will allow me to tag multiple points and label them.

I wouldn't expect the temperatures to be much different for a 4 cylinder versus a V8 as long as you assume a properly tuned engine. If you have an engine that is not running/tuned right, particularly exhaust temperatures can swing to extremes. I won't force my engine to run rich just to demonstrate that.

-Rod

[jdmccright]

Thermal imaging camera...coool.

You can also purchase an infrared thermometer from a auto parts store for $20-30. These take the surface temperatures of wherever you point the little laser dot at (though with mine, the sweet spot is actually just above the dot). The important thing about using these is to note how wide the temperature window or "spot" is for the distance you are measuring from. This is usually shown on a label having a conical graphic showing the spot diameter at various distances from the surface. Take a temp reading of the header from too far away and you will likely also be taking into account the block temp surrounding it.

They are a great, economical diagnostic tool to have and alot safer than using your hand to feel temps. Highly recommended. Good luck on your project!

[MagicRat]

Temperatures of underhood components are not consistent.

A properly-functioning cooling system will keep the coolant, block and heads at a fairly consistent temp, when the engine is warmed up.

But exhaust system temps vary a lot. Exhaust manifolds and pipes get much hotter when an engine is operating at a heavy load (trailer-towing, driving up steep hills at highway speed etc) than they would at idle.

[shorod]

Inserted below are links to pages of a thermal report of my 2004 Mercury Mountaineer with the 4.6L V8 engine. These photos were captured after a 3 mile drive. I was not pulling anything, there were not a lot of hills, and I wasn't driving aggressively. The first image was taken about 1 minute after shutting the engine off (long enough for me to run downstairs and grab the camera).

A few things to keep in mind when viewing these:
1. I chose an emissivity of the material that was of interest at the time - cast iron for brake rotor and exhaust manifold, dull aluminum for engine. The emissivity will have slight effects on the min and max temperatures.
2. I guessed the humidity to be at 65%, but actually it was more like 100% (it was raining). Again, the humidity will have a slight impact on the temperatures.
3. The heat shields over the exhaust manifolds obviously make a huge difference in temperature. Keep in mind though, the emissivity was selected for cast iron so you cannot make a direct determination of the temperature delta based on the scale due to emissivity as discussed in 1. above. The inaccuracy probably is no more than 5 degrees due to emissivity though which may be negligible at these temperatures.
4. Heat is not the only area of concern under a vehicle. You also need to be aware of any moving items such as belt driven accessories, electric cooling fans, or laying something metal between the positive terminal of a battery and ground. There are also several chemicals to be concerned with.

If you would like the bare images or a more legible PDF of the report, send me a Private Message with an e-mail that can accept JPEGS and PDFs.

-Rod

[williz57]

Passenger car engines operate in a range at idle from 200F to 215F before electric fans activate to flow air through the radiator. In my experience the temp at the exhaust manifold the first bend off the head runs in a range of 325F to 400F fully warmed and Idling. the cat converter is the hotest spot and at road speeds all these temps rise exhaust manifold out to the cat converter that is ceramic and becomes very hot. Many grass fires are caused by cat converters parked in grass. The engine maintains cooling at 200F to 215F and that can vary with diff engines but basic temps. engine oil temps around 235F and important part of the cooling system.