Not to hijack this thread with opinions but if they havnt been done am I better to do the mod (and at the same time bypass one of the coolers). Or should I put a BOE cooler or water heat exchanger in the back?
Daily driver, not track days, 36k miles. No camlobe wear.
I did a fair bit of research before deciding just what to do about this.
If you street drive in North America and never do track days, you're probably fine just taking the oil coolers entirely out of circuit. Toyota didn't supply any oil cooler on US market 2ZZ-GE equipped cars, all of which are a lot bigger and heavier (thus more engine load) than a Lotus. You will need to buy one part, which is the threaded oil filter nipple that replaces the cooler adapter.
The biggest hassle to this job is getting all the oil out of the cooler loop before you cap the lines. I made quite a mess blowing compressed air through the cooler lines to empty things out.
My own personal observation (lying on a creeper under the running engine on ramps during a leak test) was that the oil warms up quite quickly if left to its own devices - tested with the high tech hand-on-filter measuring system.
The next step up the scale is to use an oil to water cooler, like both Toyota and Lotus did on their UK/EU and Australia offerings. It's compact, lightweight, made of stainless steel, and will heat the cold oil as well as cool the hot oil. Your 2ZZ Elige came with the required hoses for the factory cooler - just pop the aluminum U-tube out, pop the cooler on, and call it done. Standard list price for a new cooler is ~$500 if you can find one. The good news is that the cooler from a '90-93 Celica GT or '93-99 Camry (probably among others) can be adapted to fit, which was the route I went as I had a '92 Celica GT engine sitting around.
Next step past that is probably to go to one of the OE coolers and a better thermostatic sandwich plate. The problem I see with the sandwich plate design Lotus used is that it does not actually stop oil flow through the coolers when the engine is cold - just forces flow through the coolers when the oil is hot. There are better ways to do this. There were apparently also sometimes assembly quality problem with the sandwich plate Lotus used as well.
You can go to one of the nifty Laminova coolers, but they really aren't needed for normally aspirated street use.