47-55.1 Radiator question

[1project2many]

Unless that radiator is plugged, it should be more than capable of cooling the engine. Between aluminum construction and sheer size you should be more than covered at low load. Pusher fans are fine but I would try to build simple box or tube shaped ducts between radiator and fan to prevent air dispersing rather than install a shroud that restricts airflow when moving. And yes, the shroud in the pictures is very restrictive.

An air duct under the radiator can be very effective. The goal is to create a low pressure pocket behind the dam which draws air down through the engine comparment. It can be so effective that you can see the hood get sucked down on the highway. If the truck is overheating at idle the air dam is not the answer.

I'm not sure why folks say retarding timing will cause overheating. This is generally not true. When spark occurs it initiates a reaction which takes time to complete. We use spark advance to try and match peak combustion pressure to crank angle at 6-20 degrees after TDC. We start combustion before the crank is at TDC and the reaction continues even after the piston reaches BDC.

Retarding timing will effectively make peak pressure occur at a greater amount of crank degrees ATDC. To a point, the crank angle is greater, mechanical advantage created by the lever arm of the crank is greater, and cylinder pressure is lower but more effective. This means less wasted energy is used to heat the pistons, head, and block. But it also means the combustion reaction continues into the exhaust and can heat headers / manifold.

If spark is advanced we see a different result. Pressure begins to increase as the piston is forced to TDC by the crank. Pressure created by combustion attempts to force the piston down the bore while momentum and force created on other pistons is working to move the piston up. If there's too much spark advance we start to see big pressure spikes and heat as the "up piston" and "down piston" forces in the engine collide. First, engine oil endures extreme pressure as the rod bearing is forced toward the crank. This very quickly heats the engine oil which can result in oil thinning and even contact between bearing and crank. If the engine continues to operate with excess advance, energy that cannot be used to move the piston down is shed in the form of heat. The piston tops, cylinder head, and block are be quickly heated. Heat will transfer out of these parts but it happens more slowly than it is being added. The only way for pistons to cool are through contact with oil, by splash or from oil cooling jets, and by contact with the cylinder walls and minimally through windage. The primary cooling method for the heads and block is through heat transfer, first to coolant then to radiator then to air. It's very slow and can easily be overwhelmed. If you have old, heavy cast heads and / or a block with poor circulation paths it only delays heat transfer. And if any steam pockets form, well, you've just reduced heat transfer to near zero in those areas.

The absolute best approach is to reduce the amount of heat that's transferred to the heads, block, and piston. Especially on an engine that doesn't need to achieve maximum power or efficiency. I can tell you from experience that 2-3 degrees too much advance at cruise is enough to quickly take out bearings on a forced induction engine without any audible or performance signs there's a problem.

I would not be afraid to reduceg peak advance by 2 - 3 degrees and then monitor coolant temp. I would seriously consider installing an oil temperature gauge to monitor the effects of timing changes and changes in weather or fuel. And I would think about using a "wide band oxygen sensor" to check the air:fuel ratio of the engine as it operates through idle, acceleration, and cruise. Either I would buy one to use while driving or I would rent time on a chassis dyno. These tools and methods are frequently used in todays world of EFI tuning. When these tools are used correctly engines achieve higher levels of power without sacrificing reliability.

I would also consider adding an engine oil cooler to help ensure engine oil is not overheated. The engine oil cooler could be placed in a different location so as not to affect air intended for radiator cooling. An oil cooler placed under the radiator, like an air dam, might be very effective.

Your mileage may vary.

[TX3100Guy]

The saga continues, but hopefully I have the problem on the run. Here is what I have done so far to get a cooler running truck.

1) Adjusted timing
2) Installed a 160 degree thermostat
3) Replaced the multi-section lower radiator hose with one with spiral coil inside
4) Temporarily removed the AC condenser to get a free flow of air to the radiator
5) Re-gapped my spark plugs, not sure this does anything, but it is a change
6) Installed an air damn directly under the radiator support
7) Went from one pusher fan of 3,000 cfm, to three 2,000 cfm fans for a total of 6,000 cfm





I'd be driving it right now, except I seemed to have misplaced a plastic insulator that goes between the magneto cap and the internals. Until the replacement shows, up I can't run the car. It shoud be here by this weekend, so more to come......

[nvrdone]

you mentioned you replaced the lower hose with one that has a coil inside. Does the top one also have a coil? If there is no coil in either hose, they could be compressing and causing a flow restriction, there by causing an over heat problem. I had a 392 hemi that had what sounds like the same problem. The correct hoses solved the problem.

[e015475]

Running a 160 degree thermostat is going to hurt you, not help you. It may take the engine a while longer to overheat, but you're reducing your cooling capacity with this thermostat. A low thermostat isn't doing your engine any good either.

The rate of heat transfer out of a radiator is always a funtion of the temperature difference between the radiator and the outside air. To maximize heat transfer you want the radiator as hot as possible relative to the air going over it.

6000 cfm of fans is likely overkill and your truck is going to sound like a vacuum cleaner going down the street, especially if they're in front of the radiator. Doubling or tripling the flow through the radiator isn't likely to make it cool much better and will just make it noisier - cooling capacity isn't linear with flow velocity

I'd suggest that you install a PWM fan controller with a temp sensor to slow the fans down and match demand.

Also, water has better heat transfer than antifreeze. I'd only use as much antifreeze as was necessary to protect from freezing in your area and no more. The ideal situation would be water and some Lubeguard for corrosion protection, pump lube and some wetting agents.

Just my 2 cents...............