I've spent the last few days reading posts on here regarding cooling issues and possible solutions, and I'm still having problems with my 383 after trying some things.

The motor is a 383, stock-ish heads, HEI Supercoil ignition, holley 650DP. Comp Cams 280H cam. 180 degree t-stat with two 1/8" bypass holes drilled. Installed in a 67 camaro. The motor is freshly built with only 300 miles on it. Running 10-30 oil with one oil and filter change after cam breakin. Initial timing is set at 8 degrees BTDC. Stock size pulley's, "high flow" water pump (at least that was the description of it).

When driving the car, the temps stay around 180-190, sometimes close to 200 when I'm climbing hills (during 100 degree weather), which is fine. However at idle the temp will slowly rise for what seems as high as you let it. I normally shut it down when it reaches 215. Originally I had a stock SB radiator and fan shroud, mechanical fan. Air fuel mixtures on carb set for highest vacuum.

Things I've done so far:

- Replaced stock radiator with larger aluminum radiator and 16" electric fan and shroud. Fan kicks on around 185 degrees. This seemed to slow down the speed at which the idle temps rise, but they still within time will rise to 215 (and above if I let it). It does take awhile to get to this temperature, maybe 5-10 minutes if it was previously at 180.

- Replaced thermostat with another 180 degree with two 1/8" bypass holes drilled. No change.

- Drained coolant, replaced with 20-30% coolant, and the rest distilled water and a bottle of Watter Wetter. Noticed very little change if any.

- Did plug check, noticed car is running a little lean, stepped up Holley jetting from 67/73 to 70/76. Noticed increase in performance, but little to no change in idle cooling.

- Checked if Vacuum advance was working, it was not. Ported connection was not producing enough vacuum at idle for the can. I moved the connection for the advance can over to the Manifold port. Vacum advance is now working and idle timing is higher then the initial 8 degrees. This had little to no change in cooling.

Not sure what to try next. The radiator and fan setup was purchased new off of ebay and is the same setup I've seen other members of the forum use. I thought of maybe trying to replace the fan with a higher rated CFM fan. I looked and according to the seller's description, the fan is rated at 3000 CFM. I tried to find one that was rated higher, and noticed that the 3000 CFM rating is close to the highest they sell. This makes me question how true the actual rating of this fan is. The fan seems to be drawing some air through the radiator, a plastic bag will stick to the outside of the radiator, so some air is flowing through at idle. However putting your hand an inch away from the outside of the radiator, you feel very little suction if any, so I'm thinking the fan may not be as good as was advertised. I have an actual Flex-a-lite 16" fan arriving in a couple days that has a known rating of 2500 cfm, so we'll see if that makes a difference. The other thing I noticed is that there is a gap in some places of an 1/8" to 1/4" between the shroud and the radiator. I plan to seal this somehow and see if that makes a difference.

Anything else you would suggest I try? Should I bump my initial timing higher? It seems some people say that you should set it at 12-15 degrees BTDC.

Is maybe my alternator/battery not supplying enough power to the fan at idle to run full speed?

Thicker oil? The weather around here has been around 100 degrees.

Any other ideas?

Thanks!

- Colby

EDIT - I've also tried a different 16LB radiator cap. I've run the system without the cap up to temperature a few times to try and get any air out of the system.

Since your driving temps in adverse conditions are fine you have an air flow issue when idling. By swapping to an electric fan and alum radiator you've proved there was nothing wrong with your old radiator and the mechanical fan did about as well as the electric under the conditions you have.

Start looking for reasons the fans are not moving enough air at idle. Do you have AC or a trans cooler blocking the radiator core? Excessive header heat or something else not letting the air flow you have work? Something else to look into is if the water pump is flowing enough at idle. What happens when you are stopped and bring the rpm up about 500 over idle?

As for the ported source not adding timing at idle it shouldn't. You have to crack the throttle before vacuum is present on a ported source..

Here's a quick answer to cooling issues: airflow!

If the vehicle can drive down the road and the engine stays cool, the water is being sufficiently cooled by the radiator, and sufficiently moved through the cooling system. The air flow through the radiator is dissipating the heat.

If the same vehicle overheats while at idle, it can only be that there is not enough air moving across the radiator core to dissipate the heat, or that the water is not being moved through the cooling system fast (or sometimes slow) enough.

Since the cooling system restricts coolant flow until the t-stat opens at 185 slow moving fluid is not normally the case.

Think about what is happening when you are driving down the road and the engine is being cooled. . .air is being pushed through the entire core of the radiator at whatever speed you are driving. Every square inch of the radiator is removing heat from the coolant and passing it on to the air.

Now what about when you are sitting in traffic? Worst case, you have a single fan without a shroud (and most likely a "boated" cfm rating). Air is only being pulled through the radiator where the fan blade is. . .so only a 16-inch diameter area for most cars. The rest of the radiator is not seeing air movement, and is mostly useless.
So you add a shroud. Now, if you sealed the edges, and the fan has enough a$$, the entire radiator core is being utilized. However, if your shroud has openings the fan will pull air around the shroud before it pulls it through the radiator.

Now, all you need is a powerful fan. Take a look at how the manufacturer rates the cfm of a fan. If you look at SPAL you'll see they provide a "Static Pressure" chart with each fan. The high cfm ratings you see are normally taken in "free air" (no resistance). As soon as you mount a fan on a core, you have resistance (the fan must pull air through the radiator). So your 3000cfm fan doesn’t really pull near that amount.

I had almost the exact same problem with a 383 I put in my 68. I had an aluminum radiator with an electric 3000 cfm fan I could switch on manually if I wanted but it still wanted to climb in temp. My engine guy reccommended a 160 t-stat whichh I did but didn't seem to help much.

I'm not sure if I have it completely solved yet, but going from 6-8 degrees BTDC to 16-18 degrees BTDC made a big difference. it idles smoother and runs cooler. I still need the fan when not moving, but on the road it's fine.

Also, I didn't set the mixture for max vacuum. I started at 1 1/2 turns out and was getting some backfiring, so I bumped it to 1 7/8 and it's better now.

Hope this helps.

Thanks for the responses. I don't have a trans cooler or anything else blocking the radiator. The headers are old headers I used on my old previous 350 motor that didn't have any cooling issues. I haven't tried revving the motor a little to see if it cools down (water pump flow issue).

So the suggestions so far are:

1. Seal the radiator shroud
2. better fan (such as spal)
3. bump timing to 16-18
4. Possible water pump flow issue at low RPM.

I'll give these a shot, thanks.

..........3. bump timing to 16-18


I'll give these a shot, thanks.

Bump the initial to 16-18 provided the total is around 36. If you have only 8 right now that would suggest your mechanical is around 28.

I don't know why my set-up works but it does work "GREAT". I have only seen my temp go up to 200 degrees after a 35 mile run down the freeway here in Fort Worth in 108 degree weather and I got off and sat at a stop light for about 5 minutes. My cruise RPM on the freeway is 3000-3200 @ 60-63 MPH. My temps are always between 180-195.

I have a Stock SBC replacement Summit aluminum radiator (only because it was cheaper than replaceing my stock 4 core after I damaged it). I also run a 180 T-Stat, a stock SBC fan shroud, a 17inch flex fan and an Edlebrock aluminum water pump. I have the largest Perma Cool trans cooler with -6 AN fittings infront of the Rad.

I used to have a 14 electric pusher fan in front of the rad for just incases but in 5 years of running the car in Atlanta and now here in Fort Worth I have not used it so I removed it.

You can see pic of my set-up in my signature at my Photobucket page.

My engine is a 388 with Iron heads, 10.9:1, timing is 16-18, carb is dead on, and a healthy Comp solid lifter cam.

- Checked if Vacuum advance was working, it was not. Ported connection was not producing enough vacuum at idle for the can. I moved the connection for the advance can over to the Manifold port. Vacum advance is now working and idle timing is higher then the initial 8 degrees. This had little to no change in cooling.

That says that your vacuum advance unit isn't properly matched to your engine's idle vacuum characteristics. You need an advance unit that's fully-deployed (pulled to its stop) at a vacuum level at least 2" Hg. below your manifold vacuum level at normal idle. What's your manifold vacuum reading at normal idle?

:beers: