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MG MGB Technical - How hot do parts get

I want to get an infrared non contact thermometer. So I want to know how what maximum temperature I might want to measure up to.

How hot do brake discs, exhaust manifolds or turbo chargers get?


David Witham

David; I had a contact thermometer a few years ago, I gave it to my son to use on his race car. I did some checking on my MGB but didn't record any figures, I think I remember seeing 300-400 degrees on the exhaust manifold and a max of around 250 on the head after a shut down. The thermometer measured up to 800 degrees as I recall. I did measure some brakes on his Legends race car but I cannot recall the readings.

Clifton Gordon

These are nice since you can't always be there when the object is hottest.
CD Dewey

Exhaust gas temperatures normally are in the 1100F range, more if there is a problem; EGT gauges typically go to 15-1600F. In some situations the external pipe temp can get well over 1000F. Brake discs can run to the same range in racing or in a fault situation. It is not unknown for ex pipes to glow red (C1200F), and for discs to approach white hot (>1500F). These temps will only be seen if measuring under load, as they drop very rapidly once the load is removed.
FR Millmore

David, it depends on what else you want to use it for. Cast iron melts at around 1200 Celsius, aluminium at around 660 Celsius. I wouldn't expect the engine block to go over 150, you might see 200 right at the exhaust ports.

Exhaust pipes generally get a dull cherry, which would be 800 Celsius.
Martin Layton

For everyone's knowledge, there are several different types of non-contact infrared thermometers. A lot of them are trash, while there are few good ones. However, with any of the infrared units you need one that you can adjust the emissivity. Otherwise the temperature readings will not be accurate and can/will vary more than 50+/- degrees. Emissivity is the measurement of reflective energy. All materials will absorb the infrared laser from the thermometer and only reflect so much. Only a perfect "black body" will reflect close to 100% of the laser. The amount of reflection is the temperature your unit will read. Metal (aluminum, steel, iron), plastics, wood, etc., all have different emissivity values. If you do not have a unit with adjustable emissivity, it is almost worthless. Two companies that make very good non-contact, infrared thermometers are Land Instruments and Raytek. Raytek is the company that makes the small unit you see in catalogs that cost about $100, but is basically worthless. The more expensive, adjustable Raytek units are good. Land Instruments has an excellent unit that will fit into a shirt pocket and has adjustable emissivity. Due to my profession, I have three different Raytek units (on was almost $5,000) and two Land units. I prefer the Land thermometers. Also, most of the infrared units are calibrated for temperatures from 0 to 1,200 F, and others from 0 to 1,800 F. Once, the A/C on one of cars was just not blowing cold. I took it to the shop and they used their little cheap Raytek infrared thermometers and they said that the air was blowing at the correct temperature. However, when I pulled out two of my units and adjusted the emissivity for the plastics vents, I showed them that their temperature gun was off as much as 8 degrees F. It turns out that the temperature unit in my car was bad and I showed them their units were wrong.
Robert Browning

I use a laser non-contact thermometer like this one. It measures from about -50 to +1000 F (500C) and works quite well. There might be something similar in the UK.
Phil O

Thanks for your help everyone.

Robert's comments concerned me at first. When I started thinking about it I became less concerned because I think I am more interesed in comparative temperatures than absolute temperatures. Eg. How much hotter is the top of the radiator than the bottom or which brake cliper is dragging or when he shower runs cold is it because my children and wife have used all the hot water.
David Witham

David and Phil,

I was not trying to scare anyone, I just wanted to be sure everyone understood just what David said. The smaller cheaper units such as Phil has pointed out are OK for "comparative temperatures", but if you need more accurate/precise information these small units will not be satisfactory.

By the way, I DO NOT work for these companies, I am just an end user like all of you.

Robert Browning

This thread was discussed between 05/02/2007 and 06/02/2007

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