On my 85, I currently have a stock radiator, and the Z51 oil cooler/warmer sandwich above the oil filter.

On my last trip to the track I hit 265F coolant and 305F oil temp on a 70F day, because of the sustained high revs. I pulled the shroud but didn't find any blockage in there. There's a small 1/2" gap under the a/c condenser that I blocked off to keep debris out... some say that hurts airflow to the radiator, but it's very restrictive anyways due to the shroud plastic, so I'm not convinced. But I'll remove it anyways and use a screen to keep debris out.

I'm avoiding putting in a racing radiator because it's going to require me to replace my a/c condenser with a thinner one and dealing with capturing the R12.



Option 1: I can do an external plate oil cooler for about $80 mounted on the cross member behind the radiator fan, plus $100 for a oil filter adapter with thermostat, and $170 more for all the fittings. Solves oil problem but not coolant problem. Add aftermarket radiator later ($500) and replace condenser, recharge R12.


Option 2: Install racing radiator with internal oil cooler. Nobody makes one for the 84-89. Ron Davis wants $200 extra to add one to their $540 radiator. I haven't asked DeWitt yet, but I presume it'll be close to that also. I still need the fittings and hoses ($170) plus an oil filter adapter (no thermostat) for $40. And then I'll have to still change the condenser.

Option 3: Shift sooner and run slower lap times.


First choice is a little cheaper, but takes up more space and leaves me with more fittings. Also the oil thermostat opens from 160-180 which I think is a little cool for street driving.

But the 2nd choice just dumps more heat into the radiator, so it won't cool either the coolant or oil quite as well.

What do you think? Am I missing anything?

I like the Dewitt idea.

The stock radiators just do not have enough surface area to cool things off. Toss in that pointless oil heater and it only transfers more heat to an already taxed system.

I would consider a separate oil cooler, with a remote filter. It would add another quart (at least) to the system. Same with the Dewitt, it adds a bit more coolant to the system.

I question how important the thermostat in the adapter would be especially where you guys live. It would probably work just during initial warmup.

Some guys at the track with inline thermostats have been taking them out, mainly because they weren't working correctly.

I have an Derale external cooler with the oil filter adapter for sale. New never used. Summit p/n DER-15503 - Summit-$88.00
$50 plus shipping.

Remote filter just adds cost. The filter adapter goes where the stock cooler is, but instead it sends the oil out to the external cooler or radiator. It also can contain a thermostat to bypass the external cooler if the oil is cold. (Not needed for a internal cooler in the rad, because the coolant helps warm it up.)

Hey, it still freezes in CA. The car sees some 40F driving conditions, and if I'm headed up to my dad's place a few hours away it could be below freezing.

The oil cooler is going to result in pressure loss, and if the oil is cold, that's going to be huge and might be starving the top end of the engine for oil.

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Didn't think it got that cold down there.

I wonder what the pressure loss would be. I've never seen any calcs.
And the oil pressure's higher when the oil's cold. I get 110 lbs cold in a dry sump and 55 hot.

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Don't forget though, an internal radiator EOC won't begin to warm the oil until the coolant thermostat opens up. I have a Dewitts with an EOC. In cool weather, I plug up an oil warmer, set on a timer to come on a few hours before morning. The warmer is an external pad adhered to the bottom of my oil pan. It raises oil temp about 30-40 degrees above ambient temperature.

With a remote filter you can relocate it so it's not sitting right next to a header.

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We use those external warmers on the drysump tanks. Some of them are fairly fast, like 20 minutes to hit 140.

Good point on the Dewitts with the EOC. With an external plumbed cooler, the warm up won't be affected much if you're at a stand still. And if you're driving in cool weather, the warm up's only going to be a couple of miles further.
I usually warm up the C4 to 100 degrees before I drive it and never hammer it until the oil's hot.

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Higher at the sending unit. But that's just an indicator of how thick it is, not that it's flowing well.

It's amazing to me how much hotter your car runs compared to mine. I do have my hood vented in multiple places though. Also an aftermarket water pump. Have you cleaned the cooling system at all? I've run some of the Prestone cleaner in it and done full drains from the block. Perhaps all you need is a pump that's decent at higher RPM.

I have a stewart pump with larger impeller in a stock housing, high flow stat, cooling system is flushed about yearly. Radiator is an oem replacement and not the heavy duty 2 row.

I wonder if they gave you the non HD radiator? Just a thought. By high RPM, how much are you turning? I have the inner fender liners off, the cowl seal cut, the underhood lights out, and holes drilled in the upper fenders plus the leading edge of the hood. Hard to believe that would add up to 70° cooler. Might be worth trying some venting.

I don't think the HD radiator is available anymore. There's some turns at the track where an extra shift would slow me down, so I'm hitting up to 4800, even though my shift light is set at 4200.

Why do you have to replace the condenser? Is there less space up front in the early C4's? I have a '93 with a Ron Davis radiator, the stock condenser, plus an external tranny cooler and oil cooler in front of that. Everything runs nice and cool, even here in AZ.

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The 85 has a different radiator and cooling setup.

Kevin, have you looked at possibly converting to the 90 style in your car. You should be able to pick up all the mounting stuff from a salvage yard.

But on a side note. I think your best bet is to get a heavy duty rad from RD or DeWitts and then do a stand alone oil cooler and get rid of that piece of crap GM incorporated into the early cars.

I've considered that. I'd have to take a close look at both setups side by side to see how feasible it is. It would also make the radiator cheaper since Dewitts has one for the 90+ with oil cooler in it, for $150 less than the custom price quoted by Ron Davis.

But I'm gonna give the air-cooled oil cooler a shot. If anything, it'll mean a little less heat going into the stock radiator (via the factory sandwich cooler). So that buys me a little more wiggle room with the stock radiator.

If you can use it CC, I just posted a NIB B&M Super Cooler in the F/S section. It's their biggie.

I would highly doubt the factory sandwhich cooler is doing much good, as it is ingesting coolant into the sandwhich. It's not doing much cooling of anything.

Best bet is to yank that thing out, plug it off and get a canton adapter and go from there.

Theirs are pretty pricey and don't have a thermostat built-in. Without a thermostat, the rad with EOC is a better choice.

Thermostats, you don't need one. Just block off the cooler.

Hey Kevin, here you go.

http://forums.corvetteforum.com/showthread.php?t=2170396