C5 Occasional HPDE; new Radiator - EOC?
 

I'm planning to replace the original radiator in my basically stock C5 that I use for occasional HPDE days (1-6/year) in California. This would be preventative, as it's not leaking, but it is 16 years old, with >155,000 miles.

My next day at Thunderhill in the Central Valley will be in late August; temps could easily exceed 105*F. Typically, in a 25 minute session, I will see engine oil temps max out around 270-275*F with ambient temps >95*, so I don't think a separate EOC is justified, especially since 99% of my driving is on the street.

However, the reason I'm looking at a replacement is to avoid concern with those plastic side tanks, so I was looking at DeWitt's. The difference in cost is only +$80 for an integrated EOC (plus ~$250 for the block adapter and associated plumbing.)

On one hand, if I'm going to the expense of an all-aluminum, dual-core radiator, is there a downside (aside from cost) to an integrated EOC? On the other hand, is bringing down max engine oil temps ~30* really necessary given my limited track time?

Thoughts?

I was just at Thunderhill last weekend. On the west course doing an autocross. I have a Ron Davis with an internal oil cooler. My oil temp never got over 207. Granted it's just an autocross. When I'm usually autocrossing in Crows Landing my oil temp will get to 225 by the end of a run, get back to grid and by the time I start the car back up it's down to below 200. This was as recent as the 4th of July weekend.

I have a Ron Davis with the oil cooler and see temps around the 260-275 depending on the temp, track, etc. I would say if you are going to replace it may be a good solution but what oil are you running? May be a cheaper alternative to run a thicker oil for track days. I run Mobil 0w-40 but the general consensus is that the 300-degree mark is the cutoff. Keep that in mind.

I think it's smart. I have one, however never hooked up the eoc. There is some extra work to it, but seems like the ticket for your use. I'll be selling mine when I sell the car, but not in time for you probably.

:)

I run a DeWitts with EOC which I have not plumbed. I run a stand alone EOC and still see 270 so I know the radiator EOC would not be enough. With that said, I'd get the DeWitts with the EOC as it sounds like this would work for you given your current oil temps. Maybe not plumb it in until you need it. An unused internal EOC really doesn't degrade the cooling capability, but it's gonna save you money over a stand alone setup and is a better option for a mostly street car.

I have a DeWitts with built in EOC. I live in northeast with chilly spring and fall and cold winter. When street driven in colder weather the temp will stay around 170 unless I keep the revs high. This isn't good, its to low - ideal temp is greater than 200.

This may not be an issue in California with its warmer climate but in a car that sees cold temps and is 99% street driven I wouldn't recommend a EOC. Although a thermostat controlled bypass would probably solve the problem.

Hey Craig, I would go with a Ron Davis or Dewitts radiator without the EOC. I was always told running a stand alone EOC is better.

If you are dead set on an Oil Cooler I would say for your use the integrated Radiator/EOC is your best bet. If you with with a stand alone unit you're still looking at needing the sandwich plate and plumbing but then you'll have an extra radiator to place somewhere.

An oil cooler may be a good idea if ambient temps will really be 105+. You'll be glad you had it when you get faster and the oil temps get MUCH higher. On our tiny track here in Iowa last month in 78F ambient temp, I was still hitting 295F oil temp with no coolers. You'll get much higher than that.

This is a good point for winter driven cars in colder climates.

:)

I have an EOC - same occasional HPDE for now. I live in New England and run the low profile improved racing thermostat. No issues getting to temp around town. Plus you can run a bigger cooler for the track. I'll see how it performs on track next week.

always run your EOC seperate. you will get better cooling, and the rad will cost you less.
since your in california (like us here in Texas) and you only have a 6 quart wet sump, you dont need any help with oil warm up. which is the only advantage to a rad with EOC.

keep the seperate.

Are you talking water temp or oil temp? Are you talking cold weather or summer? Getting oil temp above 200 on a cold day with DeWitts is my problem. I even tried putting cardboard in front of the EOC side of radiator, no help. I'm talking just normal driving - you know, 1700 rpm going down the road kind of stuff. Driving hard, sure, that will warm the oil up regardless of ambient.

That's odd. I ran the Dewitts with internal EOC when I lived in NH with no problems getting oil to temp even during 6th gear highway commuting -- oil would usually run 10-20 deg above coolant temp in normal driving. I was running the stock thermostat, not the 160-deg T-stat.

You really need the temp-based bypass. In Florida weather, with the AC running, my car idles at 201 with an EOC. At Sebring, temps peak at around 275 after an hour of lapping, much less if running 30 minute sessions.

Thanks for the opinions and experiences, everyone. I think I know what I'm going to do - just a new radiator without integrated EOC.

I already have lots of track laps on this motor without an EOC, and with the number of HPDE events I do each year, it's unlikely that I'm going to get significantly faster, or start building much more heat. Plus, the sessions only seem to be getting shorter. I used to drive mostly with a group that only had 2 run-groups; 30 minutes on/30 minutes off. Now, I'm lucky to find an event with only 3 run-groups, sometimes 4, and they're usually running 20-25 minute sessions max.

If I do need an EOC, it sounds like a separate unit is preferable, although that choice comes with warm-up issues for street driving, requiring a thermostat.

:thumbs: Good call, that's what I'd do.

When I looked into it, there was some discussion and more than one complaint re: the thermostats being off or not working at all. Added complexity & all that.

:)

I'd run separate coolers. Easier to route cooling lines and more efficient.

After some thinking I bet you will see a slight drop in your oil temps with just the upgraded radiator. With the small amount of track driving this is your best best.

If you do get a oil cooler just make sure you get a thermostatic plate, this will make sure your oil is up to temp before it opens.