Hey guys,
In case anyone is interested, I thought I'd post up my work trying to address my overheating issues. Maybe it will help someone out there somehow.

I haven't posted much of anything lately because my family has been on a debt payoff blitz, and we haven't budgeted anything towards car projects or hobbies. Lately I've been able to sell a bunch of stuff around the house and decided to use some of the proceeds to attack my overheating problem.

Background
I put this 409 SBC in the car in late 2008. I only had a couple weeks to do quick tuning & basic debugging before putting it up for the winter. In the spring and summer of 2009 I rebuilt the front & rear suspension & differential and TIG welded a new exhaust system (starting with a Magnaflow kit for the raw materials) and resumed tuning in earnest. In-town tuning went fine, and when I was feeling comfortable I took it on a road trip to Kansas City from central Illinois.

On the road trip, it became evident that I had a cooling problem that didn't show up in town. That's right, at slow speeds/idle/in town it didn't overheat at all. I had done all the right things that had always worked for me before- new engine, new GM water pump, new hoses (yes the lower hose has the spring), flushed radiator, new H/D fan clutch, original pulleys, 50/50 water/antifreeze mix, new 180* thermostat (brass high-flow), iron water neck, original shroud, original air dam in place & serviceable, etc etc etc. I experimented with timing and watched the fuel mixture on the laptop (using an Innovate wideband A/F gauge) although I didn't have a timing light with me- AutoZone was kind enough to let me use one in their parking lot once. When I got to KC I borrowed Dad's timing light and bought a vacuum gauge to monitor about everything there was to monitor, but nothing helped. At 60 MPH, the temperature was steady. Below 60 MPH, all was good. Above 60, the temperature rose without bounds- I couldn't stand to run it over 235* so I usually slowed down when it crept up to 225-230*.

Anyway, after going through the carb (working with Cliff Ruggles), it is now running sufficiently rich that the mixture is ruled out as a root cause, and it's still getting hot at highway speeds.

Digging for root cause
I've been digging through tons of old CorvetteForum.com and DigitalCorvettes.com posts trying to figure out what to do.

I'm convinced that the aluminum heads are conducting enough extra heat into the coolant that the stock radiator's heat dissipation capacity has been exceeded. 60MPH must be the tipping point beyond which the engine's heat generation is beyond what the radiator can handle. I think I've pretty much eliminated any other variable.

Time to get to work
I just pulled the car out of storage in early June. I had to fix the rear window first (it was actually falling out!) so I upgraded it to a removable one. I finished this (other than getting some new or used halo panels) last week. Now that the window is done, I can get to work on the cooling.

This week I ordered a new DeWitts radiator. I also swapped the H/D fan clutch for a Hayden Severe Duty one (as came on the '73-74 big blocks). While the original radiator is out of the car and the new one is on order, I took the time to do a little engine compartment cleanup.

I powder coated the hinges, radiator/shroud brackets, core support bracing rod, the lower 90 degree brackets, and some misc. bolts in semigloss black. I had the core support powder coated semigloss black at a local shop. I also made some brackets for a new transmission cooler out of aluminum tonight and plan to powder coat them semigloss black tomorrow. I bought some new blackened stainless bolts to mount all this stuff from Totally Stainless and ordered new core support/shroud seals, radiator cushions, and a replacement air dam from Dr. Rebuild. I also washed out the engine compartment with soap & water, painted the frame crossmember with semigloss black RustOleum and painted the inner wheelhouse walls with Eastwood underhood black using my airbrush. Here are some pictures of all that:



This weekend I need to drain the block, powder coat the transmission cooler brackets, make up some steel lines to plumb as much of the new cooler lines as possible with hard lines, and maybe start mounting the amplifiers (I never got around to it before we decided to get out of debt, I already had them) in the jack/storage compartment if I have time. I can't do a lot more until the radiator shows up.

Geeze the prep work alone is incredibly impressive! I'm looking forward to seeing the results on the temperatures.

Matthew

Wow awesome work Doug, can't wait to see the finished results in person.

Thank you, guys! I'm looking forward to another get together too, Matt. I don't know when I can make that happen, but it needs to happen sometime. Maybe we can try again to meet up with Curt.

Quote:


Curt lives in New York now, but he'll be in town he's thinking the 9th of this month.

Don't know when the next time after that would be.

The new radiator arrived on Monday, and I took yesterday off to get it installed. DeWitts makes some quality stuff. The only real fitment problems I had was that the petcock interfered with the radiator support a little bit (a little love from a bench grinder took care of that), and the radiator filler neck position was correct for the overflow tube but the cap isn't in the correct position when it's fully locked into place. Pretty minor gripes really, and I'm not building a Bloomington Gold piece here, so all-in-all I'm satisfied. Delivery was 2 weeks instead of the quoted 2 days, so don't believe DeWitts when they tell you when it will ship. I had to make it up to the wife when the car was broken down in the garage for a week and a half after I told her it would be running.

Here's the finished transmission cooler mount on the newly powder coated core support:



The new radiator:



Putting it in the car:



Ready to take a drive:



Hopefully tomorrow (Friday) night I can get some highway tests done to see if I've licked this problem or not.

Well, I can't seem to get to the full-size pics, but it looks good from here.

Looking forward to the post-drive report.

So Doug, you got an automatic radiator...cooler tank on the side, and then ran an external cooler? Had you planned that at first?

See I did the same thing but I ordered a manual car radiator so it wouldn't have the tank on the side or the dead bungs...just radiator.

Yes I did. I consulted my transmission guy and he told me that the radiator tank "cooler" is really more intended as a transmission heater to get it up to temp quicker in cold weather. I figured it didn't hurt anything and it didn't cost a penny more. He recommended I do it this way- plumb in the radiator and put the external cooler in series with (but downstream of) the radiator heat exchanger.

Quote:


I thought about the same thing but figured being so close to the radiator the heat transferred from one to the other would still warm up the transmission fluid with the engine coolant. My transmission cooler is on the side of the radiator that has a T-stat controlled fan, so it's not even on until 185 degrees.

OK, pictures are fixed. I'm sorry for the mixup!

Test drive report:
Night-and-day difference. I drove it to work today, and the temperatures were consistently under control in town. When I drove it around town after work, the ambient temperature was about 90 degrees F and engine temp was considerably lower than with the old radiator. I drove it on the highway long enough at 75 MPH to be confident that engine temperature would remain under control, and it was. Highway temperatures were steady at 184 degrees. I did notice some light detonation at heavy throttle. In town, engine temperature rose to a maximum of 195 degrees.

I let it sit in the driveway and cool until after dinner with the hood up. After dinner I tinkered with the hood latch a bit (the left one had been releasing while driving) and took 4 degrees of timing out of it and made the following measurements:

Baseline: 34* BTDC @ 3000 RPM W/O vacuum advance
14* at idle (825 RPM) W/O vacuum advance
29* at idle with vacuum advance
(therefore I'm getting 15 degrees from the vacuum advance)
16" Hg vacuum at idle in PARK

After adjustment:
10* at idle W/O vacuum advance
25* at idle with vacuum advance

I took it for another drive. Detonation seemed to be gone, throttle response was FUN, and there was still no sign of overheating on the highway. In fact, temperatures DROPPED on the highway to 183*F. I noted that at 75 MPH the engine was humming along happily at 3500 RPM and wanted to go faster. Speed control was not easy as throttle response was immediate, so it was hard to avoid speeding up or letting off a little too far and dropping speed.

I'm a little tempted to see how much MPG I can get out of it by tuning the carb, but EFI is calling my name. Now that I have the overheating under control, I think I have a sufficiently robust foundation to consider the jump. I'm also pulling together the bits for a roller cam conversion, which I'll probably try to do at the same time as the EFI conversion. Now that it's finally keeping cool enough, this is getting fun again!

Glad it's worked out. Great job, too!

Matthew

Man, that's great!


And for future EFI and roller cam conversions.

Minor update- I was able to get this to the track in October. I drove it there- about 100 miles each way, she ran a 12.99 without modifications of any kind- and drove nicely home. I ran over a half dozen passes plus the round trip on a tank of gas. It was great!

Next year, I'm hoping to do a roller cam conversion and EFI. It should be good for another 75hp easily. Tuning the quadrajet has been great, but EFI won't be held back by an intake manifold that has to fit under my hood along with the quadrajet and stock single snorkel air cleaner assembly.