View Full Version : TECH: Oil Cooler Information

Adrian Avgerinos
09-18-2006, 05:45 PM
(This should really be put into the engine forum, but unfortunately we have two forums for engine information.)

I originally prepared this thread for a post on alltrac.net, but found the site down (again!) and decided to not let this go to waste:

First off, an oil cooler is designed to cool the oil for the explicit purpose of preventing the oil from breaking down at higher temperatures. Oil that breaks down shears easily which can increase bearing wear. Not good.

The good thing that is unless you plan to do any sort of open track events or live in extremely hot weather (+100 degrees), you will probably not need an oil cooler if you run decent oil (like Mobil1). Typically time, not horsepower, dictates the need for a cooler. Though more horsepower means the oil will heat up more quickly, running a 400hp engine at WOT for a few minutes at high speed is not enough time to overheat synthetic oil. Incidentally, with a quality synthetic, anything under 250 (some say 300 or even 350) degrees is acceptable. I strongly advise you to install an oil temperature (and pressure!) gauge if you intend to modify your oil system.

That said, there are numerous ways to integrate an oil cooler into the engine’s oiling loop. The most common way is to use the oil filter port. One way is to install a spin-on adapter in place of the filter which has two ports. Perma-Cool, as well as other companies, offer this:

The problem with an adapter like this is that you now have to also remotely mount your oil filter which means more hoses and more fittings. This increases cost and the chance for leaks.

Another way to go about things is to use a sandwich adapter. Similar to the stock 3S-GTE oil cooler, it is sandwiched between the block and the filter. It looks something like this:

For a street car, you will also want to think about the possible issue of overcooling the oil. Cold oil is thick which increases the pressure of the system. If the pressure is too high, seals can blow out. Not good. Installing a thermostat will allow the oil get up to proper operating temperature quickly. Perma-Cool and Mocal offer a remote thermostat that you would plumb inline between the engine and the cooler:

Mocal and Earl’s offer a really trick item. It’s a sandwich adapter with an integrated thermostat. So this would mean further reducing the number of fittings and hose in your system. Even though the price of these pieces are very expensive ($90 for the thermostatically controlled adapter versus $30 for the plain vanilla version), the overall cost may be less if you are using quality fittings.

Which leads me to fittings; Do NOT use hose clamps with standard barbed fittings and plain rubber hose for your oil cooler. The oil is the lifeblood of your engine and if a line blows off while you are the highway, you’re engine is pretty much toast. As it can be fairly costly to have custom hydraulic hoses fabricated (think about the high pressure hose running from the power steering pump to the rack) the most common choice is to fabricate the hoses yourself using stainless steel braided hose and AN (Army/Navy) fittings available from companies like Aeroquip, Eaton, Russel, Earls. Summit also has their own line of AN fittings for a great price. These hose-end fittings are typically aluminum, have a built-in swivel and are reusable (if you decided to re-route your lines some time). The fittings are typically available in a number of angled configurations (30, 45, 60, 190, 120, 180) as well as straight.

One of the most difficult parts in assembling this type of hose is the cutting of the stainless steel braiding. If you aren’t careful, the braiding can quickly become unraveled which makes it useless. A chop saw works quite well, but most of us don’t have one handy. Instead, I found the easiest way involves a cable cutter. Harbor Freight offers a 28” cutter for $20 that works well if you are careful. Some trimming with side snips post cut is needed, but other than that, it’s cake. Also, I strongly recommend the use of a heavy lubricant like a gear oil when assembling the fittings. It makes the process much easier and you’re less likely to gall the threads (aluminum likes to weld itself together under intense load). Search the internet for tips on assembling “AN fittings” for more information.

As an alternative, Aeroquip has started to offer a special type of high pressure barbed setup which is designed to handle up to 250psi. It should be a bit cheaper than the reusable hose ends, but the ends aren’t swiveled and I don’t think you can get anything but straight fittings. Something like this:

In either case, the hose and fittings conform to AN specification which mean the following:

1) ID of the hose matches the OD of hydraulic hardline that has an ID of some fraction of 16. For example, -8AN is equal to 8/16 + 2 * hardline wall thickness (~0.030). So a -8 hose has an ID of about 0.500 + 2*0.030 = 0.560

2) The fittings have a 37 degree flare and are sealed without lubricant (kind of like your brake hoses). It’s similar to Japanese Metric spec flare except that the threads are SAE (i.e. American) and not metric.

What size hose do you want? Well, as you are working with a small displacement engine, unless you upgraded to a high volume oil pump then -8 is just fine.

Oil cooler radiators are typically offered in two forms, one is a standard tube and fin design:

The other is a stacked plate style:

The latter is considered more efficient though slightly higher priced.

When shopping for sandwich adapters and oil coolers, you will find that most come with NPT fittings. NPT is an SAE spec tapered thread. Unlike AN fittings, NPT requires a sealant/lubricant like Teflon tape. It seals by deforming the threads which creates a seal. In my opinion, they’re a bitch to install because you never know exactly how tight to make it. Too loose and they leak. Too tight and you crack the part. The matching NPT size for -8 plumbing is usually 3/8”

It’s funny that you ask about this now as I just finished installing the oil cooler on my car this past weekend:

For my 3.0L engine I decided to use -10 lines, which is probably slightly too big, and I realized too late that Summit sells the thermostatically controlled sandwich adapter from Earl’s. In addition, the fittings on the thermostat and sandwich adapter are 3/8" rather than 1/2" like I originally wanted. So it’s not a perfect setup, but it will probably work pretty damn well and I like how well it’s hidden.

Direct link of a couple photos:


No clue on the performance yet but I'll be at the track next month for an open track event with NASA. I'll post results.

10-05-2006, 04:53 PM
Quick question, what's the cast part ziptied to the front crossbeam?

Adrian Avgerinos
10-05-2006, 06:30 PM
Oil Thermostat from Perma-Cool.

10-05-2006, 08:45 PM
Ah, get you now. I misunderstood with you saying you hadnt realised about the thermostat-sandwich plates being available meaning you had just used a normal sandwich and the casting was possibly a fancy thread converter AN to BSP/NPT etc.

How did you go about sizing the core for the cooler? From what I've read the 3SGTE used on track seems to need a 10row which doesnt interfere too much with road use. I'd imagine you'd be about the same size with bigger engine but no turbo heat to deal with?

Adrian Avgerinos
10-05-2006, 09:35 PM
As I bought the cooler nearly 3 years ago, I honestly don't remember how I chose the size you see here. It was probably something like "Well, that ones a bit small, and that one there is a bit big. Ah ha! This one's in the middle. I'll go with that."

That said, I'm actually finding I can't get the oil past 180 degrees on the street so I may fabricate a shield to block airflow for street driving. For this engine I'd really like to see oil temps around 200 since I do a lot of short distance driving.

10-05-2006, 10:52 PM
As I bought the cooler nearly 3 years ago, I honestly don't remember how I chose the size you see here. It was probably something like "Well, that ones a bit small, and that one there is a bit big. Ah ha! This one's in the middle. I'll go with that."

That said, I'm actually finding I can't get the oil past 180 degrees on the street so I may fabricate a shield to block airflow for street driving. For this engine I'd really like to see oil temps around 200 since I do a lot of short distance driving.

Yeah, one of the lads in the GT4dc over here found the same with a 13 row cooler on his ST205. Believe he fabbed a plate to shield some of the cooler from the airflow on the street but was ultimately going to revert to a 10 row cooler.

The problem seems to come from the thermostats being analogue devices. Dont know if digital ones exist but I'd imagine they arent cheap. :eek:

Adrian Avgerinos
10-18-2006, 06:33 PM
Back from the track. From this thread:


Oil and Coolant Temps were well within accepted levels. During the hottest part of the day (80 degrees), Coolant and Oil went no higher than about 215-220. I'd like to get the coolant temps down a bit, so I may look at improving the airflow through the radiator (I lost the stock duct panels).

I'm quite happy with the results. :bigthumbu