Cylinder Head Temp Gauge. How Hot is Too Hot?

[Fasterbrit]

This is a question that has always baffled me. VDO have been doing a head temp gauge for many years now, but I have never had concrete info on what is considered too high head temps. Anyone out there know what max head temps should be? Anyone running head temp gauges? What do you consider too hot guys?

[Fastbrit]

I used a VDO head temp gauge in my Camper tow vehicle with 044 Magnum heads on an 1835 – it would read (I say 'read' as who knows what the true temp was or how accurate the gauge/sender really is) around 270–280 degrees while cruising without load, rising to about 300 degrees when climbing a hill (with trailer). As soon as I backed off the throttle, like coasting down hill, it would almost immediately drop back to about 230–240 degrees – sometimes less. At idle, it would settle to about 220 degrees. 

[ESH]

I don't think they're generally designed for an air-cooled motor. Mine sits towards the top of the scale so I just use it as a guide. It moves a little under load and the drop you see in the rain would seem to indicate that water could be used to good effect for cooling.
 

[alex d]

readings also depend a lot on the location of the sender...I find that fitting it under the plug is a PITA so I just put it on an exhaust stud

[Neil Davies]

readings also depend a lot on the location of the sender...I find that fitting it under the plug is a PITA so I just put it on an exhaust stud

I put mine under a second nut on a head stud. Not as accurate as under a plug, but as long as you are just looking for a change, not an actual reading it's ok.

On a couple of circuit race cars I've seen the guages mounted at all sorts of angles and when I asked why, I was told that under normal race conditions, all the needle are pointing straight up - that way the driver notices quicker if something is wrong as the needle will move left or right and the thinking time for working out how different it is to normal is not needed!

[Udo]

I used a VDO head temp gauge in my Camper tow vehicle with 044 Magnum heads on an 1835 – it would read (I say 'read' as who knows what the true temp was or how accurate the gauge/sender really is) around 270–280 degrees while cruising without load, rising to about 300 degrees when climbing a hill (with trailer). As soon as I backed off the throttle, like coasting down hill, it would almost immediately drop back to about 230–240 degrees – sometimes less. At idle, it would settle to about 220 degrees. 

Hi Keith

I think with original heads and 90,5's you would have lower temperatures . We messured our temperatures years ago on street engiens and had a max of 220 . Most we backed off the throttle from 200 degrees on . 280 is real hot
On a stud like head stud or exaust the temperature is much lower than under the spark plug .
Udo

[Fastbrit]

I always used the under spark plug sender from VDO but I've never really trusted the actual readings on the gauge – I used it more to see how much the temp increased under load. Also, don't forget, I was using a fully-equipped Type 2 Camper, towing a race car on a four-wheel-trailer, with spares, tools etc... I'm amazed it did it so well!

[Udo]

i know that your engine must run hotter than in a beetle . But it is for sure that original heads with 90,5 pistons run much cooler than 044 with 94's . This combination is good for the most head temperature .

Udo