Head temps, HOT, difference between 1 and 3 Options

[yarin]

I've got two of the VDO spark plug type head temp sensors. One on cyl 1 and one on cyl 3. I know that cyl 3 is the hottest, but i'm seeing differences of ballpark 30-40 degrees between the two. From the drivers seat I can't accurately read the gauges, so i'm going to move the gauges somewhere else and see how hot the temps get.

On the track the #1 cyl gets to about 365F. The #3 gets hot, unconfortably hot for me. I thinking around 400. I tried retarding timing 5-6 degrees total, didn't seem to make a difference.

A little history: the PO was doing a hill climb and literally melted the right side of the engine (cyl 3 side). He had the head rebuilt and slapped it back together. Before I converted to megasquirt the carbs had all this metal crap (aluminum maybe) welded to the inside of the butterfly valves. I'm thinking this head really had a melt down.

#3 always run hotter than #1, even at idle. I'm going check reading on my stock injection head temp sensor and see what Megasquirt says.

It was bugging the shit out of me at the track. I kept looking over instead of concentrating on the course.

Thanks

[Jake Raby]

The stock cooling system has imbalance issues between the left and right bank of cylinders. I have monitored these temp differences at a max of 120F between the two banks of cylinders, but they generally average a delta of 60F. Number 3 will always be hotter than #1, it's the nature of the cooling system- until you swap to a DTM.

YES, head temps can raise and lower VERY quickly dependant upon load!!! You can easily see differences of 100F in less than one mile.

THE SENDER MUST BE PLACED UNDER THE PLUG!!! In 2003 I put two solid weeks of test time into finding the best possible place for the sender and under the spark plug gave use the most stable readings. The spark plug is the best place because it is not surrounded by cooling air and it is not located in the cooling fin area like the original sensor is.

I have seen a 200F difference in readings between the original sensor location and the spark plug location on the same cylinder. Anyone that uses the stock sensor location can add a minimum of 70F onto their values for "real" head temp.

The stock location was made for the stock FI system. All that system needed to know was "hot or cold" as an incremental reading was not needed. The other reason that the sensor was placed in a certain location was to monitor the cool down of an engine, basically to keep the engine from going full rich at each start up, even if you just drive 15 minutes, shut down and fire back up in 5 minutes.

The stock CHT location is for FI sensors, not CHT thermocouples. 41 Ghost, those CHT fluctuations you see are real, thats what the heads live through daily and thats why properly monitoring their status is such a good idea.

Yes, I have entire folders full of data logs to support my feelings on this topic. Understanding cooling systems and etc was my life from May of 2003 clear into late 2005, I didn't do much of anything else.