I placed the following post on offshoreonly.com. This is a site dedicated to high performance offshore boating. A marine engine will typically see extended periods of high rpm use. Oil temperatures are controlled by running seawater through a cooler, much like an air to air cooler only it uses water prior to entering the block. Cooling water flows through the block and is discharged with the exhaust gas. I posted this question but not many on there are engine builders so event though it is not apples to apples I am hoping someone here could answer this question. Basically what I need to know is if using 1/2" line with the fittings being .450" and about 60" of hose if this is restricting oil flow. To answer this we would need to know the flow rate of a high volume oil pump at 5000 rpm. Take a look at my post and see if you have any input Tim T. Post from OSO I am installing an oil cooler. The setup will include an oil thermostat and a large cooler from Eddie Marine. The size of the cooler (3x16 + 3x4 P/S) will require that I use the thermostat to ensure that the oil does not run too cool at cruise speed. The use of the thermostat requires that I have a total of four oil lines external to the engine. One to the thermostat, one out of the T-stat to the filter and two to the cooler. A local hydraulics shop can make the lines. The lines that they can make are for ½” NPT using a ½” ID line that will take 400 psi and 450 degrees. The only downside I see is that the fittings reduce the ID somewhat. The smallest ID of the fittings is 0.450”. The oil thermostat is from Perma Cool and is rated at 20 GPM. Is the ID of my 4 oil lines with the smallest size at the fitting of 0.450” using 4 lines with a hose ID of 0.5” large enough? What would be the flow rate of a high volume oil pump in a 502 using Mobil 15W-50W at 200 degrees at 5000RPM be? I anticipate with the large oil cooler that my oil thermostat, which opens at 190, should keep the oil around 220 or so max. Are my oil lines large enough? Tim T.