Too hot at idle. with a different twist

[John M.]

Re: Too hot at idle. with a different twist

Mike, we live in central Illinois. The altitude is 600 feet. After setting the static timing and the idle mixture the vacuum at idle is now 16.5in. with idle speed 750 - 800.

[Glenn B.]

Re: Too hot at idle. with a different twist

John, I don't recall the exact ohms/foot value - from memory it is in the 800 to 1K ohm range. What I noticed when I measured mine was that I could not get a steady reading on the ohmmeter on most of them - it jumped around - which I believe was because there were intermittent opens in the leads. If you can get steady stable readings - this is probably not your issue - the coil wire is obviously the most critical to check.

[Mike T.]

Re: Too hot at idle. with a different twist

Looks like we can scratch altitude as contributing to the lower 13" vacuum reading.

[David M.]

Re: Too hot at idle. with a different twist

Back up a bit and bring it back to the basics. A view from an engineer who should be in bed not on the computer at 130am...

Has this a change in operation occurred after you changed something? If so what changed?
Are all the cooling system components OEM spec parts(with exception of the eliminator)? Were talking pulley diameters as well.
Do you see any signs of the belts slipping? Now on to the deeper...

I agree the fan depth is not optimal. Blades need to be half way in and out of the shroud as well as very close to the inside diameter of the shroud. Your current fan looks much to small in diameter. This will drastically decrease the fans mechanical efficiency. Its basically looping the air flow or trapping it between the fan and back of the radiator verses a nice draw through. Which would explain why cracking the hood cures it to some extent. Your breaking that stagnate air block by giving it a less restrictive path...convection style out of the hood gap. Once the cumulative heat has built up it magnifies the effect which also explains why the temp stays high. Thou a road trip should see it drop if my theory has any meat.
Have you tried to run it without a T Stat just to see what uncontrolled flow results produce? (Noting the upper and lower hose temps)

If its running OK at speed..."182*F , yet heats up when static, this indicates to me:
1. That the fan isnt pulling air over the radiator well at idle. Does a C2 have all the rubber seals and baffels around the core similar to that the early C3s have?
2. Or the water pump impeller is suspect either out of spec with relation to the housing or slipping on the shaft or eroded. (so a fluid flow prob)

I know this sounds counter intuitive but try a 192 or 195*F HD Stant T-Stat. The HD T-Stats have better control or less hysteresis than the non HD regulars or the cheapos. And with a few degrees increase in T-Stat dwell it allows for a longer coolant dwell in the radiator, allowing more time for heat rejection. This worked for my BB Olds 442. It ran at 215-220*f with high ambient 90*f+. The 192*F HD Stant cured it.

In conclusion the low hanging fruit would be to optimize fan to shroud alignment radial, axial and even angular.

[John M.]

Re: Too hot at idle. with a different twist

David. today it was 90 F. On the humid side as well. After installing a 195 thermostat as you suggested the following was noted: warm up time diminished greatly. And the temp rise when at idle slowed greatly as well! After a 9 mile cruise on the highway and letting the car idle for 10 minutes while filling the tank with the highest octane Mobil gasoline ($55 and change for 16 plus gallons), returned home and let vehicle idle for 35 minutes. Temp at 35 minutes was 235, or just at the edge of the yellow zone on the heat gauge. A two mile ride down the highway netted temp back to 200 or possibly 210. Shut off car and could hear about 20 seconds of rumbling in the cooling system but car did not puke any coolant. Vapor lock did not occur today at any time. Not sure if vapor lock was cured by different gasoline (better?) or the fact that tank was full, but for whatever reason all was fine. The following conditions are present: air flap on top of radiator to seal core support to hood (reproduction part), pipe insulation on each end of flap to complete the core support sealing. The bypass hose between water pump and intake manifold is blocked but the heater circuit seems to let plenty of water circulate until the thermostat opens. The square opening in the fan shroud directly in front of the alternator is blocked and the stock 5 blade fan (non AC) and factory fan clutch are installed. The large triangular splash shields are removed. I feel that this condition will permit normal driving to and from Indy to attend Bloomington Gold in a couple of weeks. Upon return I will check and tailor the distributor advance curve to Dukes specs and reinstall the 7 blade ac fan. Will keep all posted on progress when this happens. Thanks to all for your help and stay tuned for more after the last week of June.

[David M.]

Re: Too hot at idle. with a different twist

Glad to help....The fact that temps come down on the road confirms that the fan is the likely culprit. Does the factory OEM fan closely match the fan shrouds diameter? If so install it and the idle problem should go away as well.

[Glenn B.]

Re: Too hot at idle. with a different twist

Unfortunately - that's not necessarily the case. There are multiple reasons you can overheat at idle but not on the road. The fan clutch, the radiator, and the plug wires are just 3 examples. Good luck David.