I have measured my MAT temp after the intercooler on my 89SE, here's what I see.
This was on a 100F (38C) day! I had just installed a new fuel pump, and this run was with an electric charge cooler pump.
Travis, thanks for the link, I had looked before for a better way to monitor the intake temp after the chargecooler. I will try this out.
On the SE I had noticed the "seat of the pants" difference on cool days here in Florida. So I converted my car to an electric chargecooler pump, and better insulated the chargecooler, intake and radiator hoses. I also went to Water Wetter with minimal antifreeze. Now the chargecooler is always much cooler than the rest of the engine, even after hard running it is never hot.
Based on your numbers, the intake temp looks pretty good, but it would be nice to have ongoing data available to see what different changes will do to the temp.
I converted my S4 to the electric pump and seperated the fluids as on the SE so I am running a cooler system than the regular radiator. I am not sure why Lotus changed to the single header tank in the later cars.
There really isn't any benefit to having a separate header tank for the chargecooler. In the single tank system, the only connection between the chargecooling system and radiator system is the air bleed hose. It does not share coolant with the radiator.
Jim I realize that the crossover of fluid between the systems in real time is minimal. However there is a small amount of interchange.
The bigger issue is that there is no way to run different concentrations of fluid in the two systems with the combined header tank. I am running only about 10% antifreeze in my chargecooler system, the rest being water with Water Wetter. This is more efficient from a thermal transfer standpoint.
How much this translates into extra horsepower, I can't say. (I have heard numbers like 0.5 hp per degree Celcius of lowering the intake temp). I do know that my chargecooler used to get hot to the touch before my changes, now it never does. So I know it is better at doing what it is supposed to do than before. The electric pump helps as does the insulation.
The regular cooling system is running the recommended 30-40% antifreeze for corrosion protection and to raise the boiling point.
Jim, I don't have the service manual in front of me, but the verbage from it indicates that there is a slight interchange of fluid. The manual actually calls the single header tank "cooling system/chargecooler" header thank. The bleed hose from the chargecooler to the T below the tank is a two way hose with no check valves, so clearly fluid can and will flow in both directions.
I am not suggesting that this has any direct effect on the temps in the two systems, but it would clearly lead to slow mixing of fluid in the two systems.
This would prevent one from running a different fluid mix.
Since I was installing an electric pump anyway, which requires splicing into the chargecooler hoses and replacing some of them, adding a baby header tank was very simple.
I was looking to create the best cooling system for the chargecooler possible without undue expense or complexity, and without adding a larger chargecooler as other have done. According to Water Wetter type products the improvement in heat transfer is significant(I am aware that it may be overhyped). The electric pump appears to have increased flow at low rpm compared to the engine driven pump which also clearly helps cooling.
I have not done before and after testing of all the changes to see what the effects are, but I know that the sum of the changes are easily felt in the way the car runs and the power it produces.
Dermot's S4 site details some of the things you can do to help the chargecooler Lotus Esprit S4, and I would guess that many chargecooled cars are running inefficient systems that are easily and cheaply improved.