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(Finally stopped lurking, just for now) Neil, The question is what do you wish to see and at what speed ? Want to avoid cracking or damaging stock heads ? Just slow down, do not drive like I do. FROM THE TOP OF MY HEAD.... I have had much experience with the temp gauges with different brand heads. I drive my car about 3000 miles a month, so far, it has been 6 months without a major mishap (always cracking, melting or falling apart heads). I bought my gauges from VDO off the Bugpack or EMPI . Jim is right some folks have these for bragging rights or do not write data down to see if what is happening with the heads, thus cause confusion. I have found that the kind of heads (German, Spanish, Brazilian, American or Mexican , different valve area design, casting, and metal alloy, I have had all), changes what the gauges will read, also your fuel mixture will change the meter reading. What I am getting to is that what the meter will read as "normal" operating temps is up to what your engine parts are, modifications and settings, if your engine is EFI or Carbed etc... Well what I am saying is that you must get used to your temp readings at what you determine as midpoint or normal operating temps. I will give you an example : My engine EFI 1600 cc stock. At 75 mph flat hwy in San Diego California for 1 hr All temps are in F . - German VW head (good) 370 degrees goes higher as road grade goes up, top temp seen 400 degrees at 70 mph , good hwy grade, (heads cracked after doing this daily. - Spanish AMC head (junk) 370 degrees temp goes higher as road grade goes up, top temp seen 450 degrees at 70 mph, good HWY grade, (the valve seats on this head melted into the head after this daily use, seen other melted examples of this brand at my local machine shop). - Brazilian Autolinea (Empi, Bugpack, CB and most Aftermarket performance heads) (1/2 reach is junk) 400 degrees temp goes higher as road grade goes up, top temp seen 450 degrees at 70 mph, good HWY grade, (the heads cracked around the sparkplug area with 1/2 reach after this daily use, some other heads found to be machined crooked at the plug area and this aggravates the problem). I have bought 6 heads in 2 years , pile decorates the corner of my garage. - American Mofoco (Machining is crap, at least what they gave me after I returned it). 325 degrees temp (cooler) but goes WAY higher as road grade goes up, top temp seen 550 degrees at 70 mph, good HWY grade, (one head dropped both valve seats in one cylinder after this daily use), the head seemed to have been machined very badly , this was visible from external inspection. 2 heads bought one head still in use on cyl #1 and #2 . Suspect that higher temps at high speed is due to exhaust valve area cooling is limited because the lack of flowthrough of the casting design. - Mexican Genuine VW head bought at Mexican Dealership (are available in USA from different suppliers). 250 degrees temp (MUCH cooler) and stays cooler at higher speeds than the others. Temps stays 25 degrees below the meter's midpoint of 350 degrees even at 90 mph for 15 minutes on varied grades. Never seen any reading above 350. Cooler temps seem to be due to the metal alloy and the flowthrough design of the air around the exhaust valves and thicker valve stem areas. See what I mean ? All readings were taken from same engine in a couple of years with no other engine modifications. Readings also depend on where you mount the sensor or sensors. No one person has a standard sensor location, not to mention engine types, sizes etc... See Jim's muddying comment ? This is where I placed my two sensors, (one on each head), at the top foreward head bolt of # 3 and # 1 head compustion chambers. I did not choose to install the sensors on the standard location as per the instructions because the location makes it difficult replace the Sparkplug and may require head machining in order for the sensor to lay flat on the surface. This location , at least to me is not the hottest area that will not give a reading to prevent head damage (intake runners run near this area). I chose the hotter area nearest the exhaust that never cools off but increases with engine load, near the exhaust valve guide area. This location and the Valve guide input I received from the VW aircraft experimenters that beat the engines up more than the VW's on wheels. I hope my info has helped. LEON MARTINEZ SAN DIEGO AND TIJUANA 69 SQUARE 73 FASTY 67 FASTY ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org