<VV> cht and oil temp question

[Jim Davis]

I concur with your oil temperature findings.   With my 1965 Corsa 140 
convert, I started out in 1966 with a SW mechanical oil temp gauge with 
the sender in a bung brazed to the pan near the drain plug.   It was 
quite a project to thread the hard cable in the tunnel and up under the 
dash.  I calibrated the gauge by placing it in boiling water before 
installation.   I was living in  Sacramento at the time, so 210 F for 
boiling water seemed a good value.  I found after a long highway cruise 
at 180 F oil temperature when I showed down and made a quick turn the 
oil temperature climbed to 220 F.  In 1971, I bought a SW electrical oil 
temperature gauge to replace the mechanical gauge and placed the sender 
in the alternator adapter. I had the gauge calibrated at my PMEL shop.  
Now the oil temperature gauge tracked the engine's output.  Top up 
showed a consistent 20 degrees lower oil temperature than top down (65 
mph, same road, same temperature).  Showing down or sharp turns showed 
only a minor decrease in oil temperature.   On 80 to 90 degree days top 
up cruising at 70 mph the oil temp stabilizes at 240 F on the 41 year 
old gauge.  I have got to be towing something over 1,500 lbs to get the 
oil temperature above 250 F.  I have towed my Fiats coast to coast with 
the Corsa four times.   The engine is basically stock (the only change 
is Allison replacement points module and a 304 camshaft) with all the 
shrouding and the 12 plate oil cooler.

It is my theory that the oil stratifies in the oil pan on long 
Interstate cruises.  This causes the hot oil coming down the push rod 
tubes and through the crancase drain holes to flow across the cooler oil 
in the pan and into a sump created around the pickup. This is why the 
oil in the pan always is much cooler than the oil in the rear cover.  
Hard braking or sharp cornering moves the cooler oil in the pan under 
the pickup so that entire oil in the pan is mixed with the hot oil 
circulating in the engine showing the increase in oil temperature when 
the engine's load is actually decreased.   Of course this is only my 
theory and is based only on empirical data.
Jim Davis


On 8/6/2012 7:13 AM, Stephen Upham wrote:
> I have a '65 Monza 110 PG that has about 10,000 on the last rebuild.  I deflashed the heads using a 12" drill bit.  It cleaned the passages very well and left tiny irregular groves to increase turbulence.  I got about a half a cup of flashing out of the heads.  Since it is a factory A/C, it has the 12 plate oil cooler.  I do not have the A/C compressor or condenser installed (money/time thing). When I got the cooler from a trusted west coast vendor, I was assured that it was completely flushed.  After I received it in the mail, I shook it ,and it sounded like a baby rattle.  I ran a magnet though the debris that came out of it, and found that it was indeed ferrous.  lI flushed that baby (the oil cooler) by filling it with paint thinner and setting it in a mop bucket and pouring hot water slowly into the bucket; a process not for the faint hearted. I did that about ten times.  I then flushed it out with a water hose, and finished the job by using compressed air to dry the pass
>   ages.  I have a Clark's deep/finned oil pan.  I have two oil temperature gauges (long story).  The sender for the first one in located in the area mentioned in the Tech Guide in the triangular area in the back right hand side of the block just above the lip of the oil pan.  That is attached to a water temp under dash gauge (not something I thought of - again, long story),  The second one is on the oil pan at the bottom back of the pan.  The block location usually stays in the 220-260 range depending on load, ambient temps, and driving conditions.  The oil pan location varies between 160 and 190.  I really don't have an explanation for the difference in the spread at the higher temps, but my figures here are based on memory, so actual recording may prove there is a more 1 to 1 ratio.  I also have a Falcon dual CHT gauge.  I placed the senders around the base of spark plugs #'s 3 and 5.  The sender connection to the wire leading to the gauge in the cabin is located in the engi
>   ne compartment. The locations at the bases of the plugs don't provide the exact temps, but I am only looking for a variation from normal, and so they serve their intended purpose to show any unusual increase in temps.  The normal temps on these are 220, and they usually remain the same, not varying more than 5 degrees one way or another though all driving conditions.  I use 30w Brad Penn oil; the "green oil".  I have been using it since break-in.  I live in Dallas, Texas and the average temps in the summer are at or above 100.  I get my highest readings when I am driving on the highway and then suddenly get stuck in stop and go traffic.  I usually remove the lower shrouds in early April and reinstall in late October.  I don't know the exact difference in temps by doing this as I have never taken the time to do a same day or similar day comparison, but I understand it can reduce running oil temps by 20-30 degrees.  Also, if you are rebuilding the engine, the piston to cylinde
>   r clearance is critical. If the clearance is even a minute fraction too tight, when the heating of the engine causes the pistons to expand, they reach the point where the extra drag causes the rod bearings to stress and fail.  Ask me how I know.
>
> In my opinion having lost an engine to overheating, more gauges strategically placed monitoring different types of heat are better than fewer gauges or, heaven help you, just the "idiot" light.  In addition, making sure that all cooling passages, and coolers are clean and unobstructed, and that quality oil and proper air flow is maintained will make for a happy engine and happier owner.
>
> Hope that helps,
>
> Stephen Upham