Question about oil coolers and oil cooling...

Refinement work continues on my "Fortus" frankenstein Lotus esprit project (347 stroker in a Lotus Esprit). Things are basically running well and I'm pleased with all systems - fueling, engine, transaxle, exhaust, brakes, etc.

She runs relatively cool generally speaking. When things get hot I have a five 6 inch Spal fans cooling the engine compartment, 2 of which are cooling a Fluidyne 6"X12" oil cooler located in the trunk area (relocated from previously being in the engine bay) with outside air supplied in a variety of ways. These fans are manually controlled with a cabin switch and relays rather than triggered off of a temp sensor.

The car originally was equipped with a front mounted engine oil cooler, right behind the front radiator. I have kept this plumbed in, and added the trunk mounted Fluidyne as per above with the idea of adding extra engine oil cooling.

My question is: do you think this second Fluidyne oil cooler is adding too much drag to the flow of the external engine oil cooling system? I don't want to stall the flow rate, nor overload the oil pump, if having two oil coolers is too much drag. Would it be wise to try to add some kind of external electric oil pump or ??

Thanks in advance.


Run the two coolers in parallel, NOT in series, that way the oil will spend more time in the cooler, any fittings etc should be arranged in a manner that flow will be in the direction reqd without any head to head style setup.

Howard Jones

Do you have any idea what the oil temps are? If you have an oil temp sensor/gauge you could do a bit of experimenting with one cooler at a time in the circuit and see what is going on.

And yes two coolers should always be plumbed in parallel. It might be a bit of a development project to be sure both are flowing oil and not simply partially bypassing the one that is more restrictive due to construction types or circuit length. Twin coolers should not be a problem out of hand but good flow in both would be an important consideration to me. This is the first thing that came to mind using two different types of coolers and circuit lengths. My guess is a single good quality 6X12 inch cooler with sufficient airflow will be enough. Aim for oil temps above 220F and below 260-270F.

Maybe put the best quality cooler up front and remove the other one? I would put it in front of the radiator in clean air if it was me. That way you have an effective and simple system with fewer connections and circuit lengths to potentially fail/leak.

My oil temps on track are solid at 240F all day long (100F air temp days) with 450Hp and water temps at 190F using a 6X14X2 Earls cooler. These are similar to the Fluidyne type.

What style/type is the front-mounted cooler as well as size? Pictures always are good.
Hi Gents,

Thank you for the information here, that's really helpful.

I had not thought about running the two coolers in parallel, but that's obviously a good idea.

I'm trying to figure out how to add the Fluidyne because on a hot Seattle day (85 degrees - hot for Seattle) just running on the street the oil temps are 230-240. I imagine a hot summer track day would push these temps to 250+ which is just too hot.

The car originally had a 2.2 liter engine, with a turbo that was pretty lazyily configured (hence the engine swap here for more power). I replaced the stock front (water) radiator with a purpose built larger/thicker aluminum rad kit - a common upgrade on Esprits for improved cooling. The stock oil cooler is in front of the radiator and is about 8"X12"X3/4."

Given that the car now has a fire breathing 5.7L SBF which is 2.5 times the original displacement, it's not surprising that some further cooling mods may be needed. So far I've added engine bay cooling, the larger front rad as mentioned above, and now thinking about extra oil cooling...and just trying to do that in the wisest most logical manner.

Quick update here. Relocated the oil cooler to the back side of the rear bulkhead with two Spal sucker fans on the other side of the (heat insulated) bulkhead. Total of 5 six inch Spal sucker fans in the engine bay to keep things cool - the 2 drawing air through the oil cooler and three others drawing in exterior air.

The oil cooler is run in parallel to the front rad-mounted oil cooler.

Having run air cooled 911’s for 30+ years now I have a keen appreciation for maintaining healthy oil temps. With doubling the car’s stock hp and almost tripling the torque it’s a struggle to keep the 347 stroker cool on a hot day.

The testing and refinement continues