Too hot at idle. with a different twist

[John M.]

Re: Too hot at idle. with a different twist

Now for specific heat numbers. After a 30 minute idle time to stabilize all of the "players", the temp at the top radiator hose was 192F and the bottom radiator hose was 150. Ambient air on the front side of the core support at the level on the right side horn. Shut hood at 48 minutes of run time with same readings and at 50 minutes 208 at top hose, 176 at bottom hose. at 55 minutes the top hose read 219 and the bottom hose was 184. At 55 minutes the temp in front of the care support same place as previously mentioned, was 131, and oil temp at this time was 199. Ambient temp in my shop was 85. By the 58 minute mark the following temps were: top hose 223 and bottom hose 186 and so tests were stopped and engine turned off. Exhaust manifold temps were as follows: Left (drivers) side from front to back 418, 521,516 and 445. At manifold-exhaust pipe junction was 420. Right side: 438,515, 505 and 490. At the heat riser - manifold joint on the thick flange of the manifold 420. A new thermostat 180 was installed before these numbers recorded this morning, was not happy with the fail safe previously used as warm up time was forever and open road water temp was about 140 - 150 - too cold for my taste. The present thermostat had no effect on the overheating with the hood closed. Idle air mixture was established using both a vacuum gauge and a tach and is stable at 750

[Domenic T.]

Re: Too hot at idle. with a different twist

I'm with terry. The odd thing here is the hood open and running cooler. Then closed and running hot!

Dom

[Don S.]

Re: Too hot at idle. with a different twist



The above photos are the fan and shroud on John's car. He was having trouble posting them so I did it for him.

[Duke W.]

Re: Too hot at idle. with a different twist

The fan hub is too short, The blades should be half inside/half outside the rear edge of the fan shroud. This may not totally solve the problem, but it should help. An OE fan clutch should place the fan at the proper depth.

Duke

[John M.]

Re: Too hot at idle. with a different twist

Duke, did the centrifugal and vacuum advance numbers or the exhaust manifold temps reveal anything to you? The shroud has a cutout almost directly under the snout for the top radiator hose, and while at idle the fan sucks hot air back into the shroud area - a piece of paper in front of the opening would be sucked in if not tethered. Used masking tape to seal the hole, not much difference in water temp but extended the time until overheating. Also removed the two larger triangular shaped splash shields under the car. Made the floor and rocker area very hot and was able to idle (after reaching a stable 182*) for 25 minutes before getting to 215* at top radiator hose. When reading 215* radiator inlet temp, the lower radiator hose temp climbed to 200. Upon opening hood the bottom radiator hose quickly dropped in temperature to 185. Top hose dropped to 200 shortly thereafter. Anyone with any experience with this kind of behavior or similar problems?

[Leif A.]

Re: Too hot at idle. with a different twist

John,
I just re-read this entire thread and I'm not so sure you have an overheating problem. In post #16 you state that the car was idling for 58 minutes before it got to a temperature of 223* at the top hose. When you shut the car off at that point, did the coolant puke back thru the overflow hose on the surge tank? I would think that a classic car idling for 58 minutes in 85* temperature and NOT overheating would be some kind of a miracle. Duke's advice on the fan is spot on but, again, I don't think you have an overheating problem. In normal driving (highway and around town) does it ever truly overheat? Again, coolant puking when you shut her down. If not, then I think you're probably just fine.

[John M.]

Re: Too hot at idle. with a different twist

Leif, the car will run at the minimum thermostat setting (182*) on the road. When at idle it will slowly creeps up, and at 210* my instruments and the factory gauge are in agreement. As it runs longer the temp will continue to rise until vapor lock occurs at about 225* and the engine will sputter and die. And yes, the coolant will boil and the overflow hose will puke in a few moments. IF the hood is opened at 220* the coolant temp will begin to drop, first the outlet water temp at the bottom radiator hose and thereafter the temp at the thermostat housing will also begin to drop. Close the hood and the temp creeps up again. This is with the intake to water pump by pass hose blocked. a 7 blade A/C fan blade and a 182 thermostat. With the stock configuration (5 blade correct fan, bar type original fan clutch and by pass hose open) the temp goes up rapidly, say 7 - 10 minutes from 180 up to 220. It will puke while running at idle then if not watched and turned off. As it is one can use the car and at normal highway speed is just fine. When starting with a warm engine (fresh from the highway, it takes right now about 25 minutes before temps get to critical point) The next step is to install a core support seal between the core support and the hood. Also I hope that Duke will chime in and let us know how the distributor advance map looks to him.

[Duke W.]

Re: Too hot at idle. with a different twist

Duke, the following is the information you requested. If something is left out just ask. First, the Vacuum advance is stamped "236" and found out yesterday from the previous owner it is a reproduction from Paragon. The initial timing is set at 8*, vacuum line disconnected and plugged, RPM set at 500 RPM. Vacuum and centrifugal advance at specified speeds are as follows. 750 RPM, 16.5 " vacuum and 22.5 degrees total advance. Timing advance obtained with dial back light, no stroboscope available. 1000RPM netted 17.5" Vacuum, and 23.5 degrees total advance. 1500 RPM was 19.5 " vacuum and 28.2 degrees of total advance. 2000 was 30.4 advance at 21" vacuum. Add the 8* initial to those to see what the engine is feeling. To be more specific about one of your questions, the centrifugal and vacuum at idle speed of 750 was 30.8*.

I can't make complete sense out of your reported data, but the VAC needs to be checked for proper spec. There are repro "236 16" VACs out there that aren't even close to correct spec, which should be start @ 4", 16 deg." @ 8". Check it with a vacuum pump to verify that it starts to pull at 4" and is at the limit at 8"..

As I said previously, normal L-79 idle behavior is 750 @ 14-15". If it's not in this ballpark the engine doesn't have an OE equivalent cam.

Total idle advance should be the 8 initial plus 16 from the VAC, which is 24, and there may be a degree or two added by centrifugal is it starts at 700, but you reported 30.8 @ 750 with 16.5" manifold vacuum.

It could be the dist. has been modified for a quicker centrifugal, so you need to the RPM start point, then at 1000 rev increments up to the limit. The OE L-79 centrifugal is start @ 700, 30 @ 5100.

Report exhaust manifold temps after idling for at least five minute. Hold the IR gun close to the surface, so it doesn't pickup cooler background radiation. Report the range.

To summarize:

1. Report start and stop points (manifold vacuum) for the VAC.

2. Check again for idle behavior - idle speed, manifold vacuum, and total idle advance.

3. Start point for the centrifugal curve (RPM), maximum centrifugal, deg. @ RPM and some intermediate points.

4. Exh. manifold temp range.


As mentioned, it is not unusual for engine temp to increase during extended idle in warm to hot temperatures, but the engine should not boil over at 225F. With a 50/50 blend of ethylene glycol and water with a 15 psi cap the boiling point is 265F. Most parts stores have cap testers, so test yours to ensure that it doesn't release until 15 psi.

Modern cars with 15 psi caps often don't have fan engagement until 230F and they don't boil over.

Duke

[John M.]

Re: Too hot at idle. with a different twist

Duke, is there an available vacuum advance unit that is specific for a 66 L79? Used the search feature and found a NAPA number but upon calling my store found that this number is no longer stocked and not serviced by NAPA any longer with apparently no substitute number.

[Duke W.]

Re: Too hot at idle. with a different twist

The L-79 spark advance map is a real head scratcher. It combines the lazy 300 HP centrifugal curve (30 @5100) with the aggressive 236 16 VAC that was used on 30-30 cam engines, and it didn't change for the 4 years this engine was in production.

Given L-79 idle behavior the 12" B26 (NAPA VC1765) is the least aggressive that meets the Two-Inch Rule, and lighter springs should be installed to bring full centrifugal in at 3000-3500. If the same engineer who set up the 30-30 cam engines set up the L-79 centrifugal would probably have been 26-27 @3000 with a 12" VAC, but it's obvious that these two calibration engineers were from different planets.

As a last note I can't tell you how many people have a "L-79", but the idle behavior is not even close because it has some aftermarket hotrod cam, in which case apply the Two-Inch Rule, so check your engine's idle behavior before you buy.

If you want to know of a good L-79 spark advance map setup that is inexpensive to implement, search for a Dec. 2012 thread started by me - L-79 dist. blueprint overhaul.

Duke

[John M.]

Re: Too hot at idle. with a different twist

Located a DT504 Sun distributor tester I can use to check distributor function. Getting ready to attend Bloomington so it will be in early July when this happens. Will post results then. John

[Glenn B.]

Re: Too hot at idle. with a different twist

John - I did not read every post in this thread carefully, but have you confirmed that there are no problems with your spark plug and coil wires? I spent countless hours chasing my overheat at idle issue (heat riser, fan, fan clutch, radiator, timing, shroud, etc, etc) to no avail. I finally checked the resistance and behaviour of the resistance of my plug and coil wires and discovered that was my problem. In my case the wires were old and had developed cracks in the internals are were much higher Z than spec. Replaced them - car runs cool at idle - no issues.

Good luck - been there.....

[Timothy B.]

Re: Too hot at idle. with a different twist

Plus, it's possible the fuel is getting hot and boiling or expanding, this can reduce the spill distance between the fuel level and nozzle then drip and flood the engine. Try it with the float level lowered (primary and secondary) about five flats or one complete turn to see if that helps.

The long idle time and temperature reported does not sound like a problem. I am not saying you can't make it better, get the rubber A/C flap that goes over the top of the core support and make sure the sides are closed off so the fan pulls only through the radiator.

[John M.]

Re: Too hot at idle. with a different twist

Glen, do you know the resistance of the faulty secondary wires. I will check ours - seems that the rule used to be about 1K ohms per foot of wire was acceptable. Is that near what you found on a good set? And Timothy, I have installed the top "flap", as well as blocking the rather large hole that is on a 66 shroud (to cool the alternator or so it appears) . Also removed the large triangular splash shields under the car. Neither the upper flap or removal of the splash guards helped when done by themselves, but the combination of the two seems to allow a little longer idle time before the temp gauge started it climb. At this time the vapor lock limits my testing since the engine sill stumble and die at about 230. Restart requires cooling off for one half hour and cranking excessively while pumping the throttle. All is fine upon restart. Car starts as if one had run out of gasoline and then dumped a few gallons in the tank after waking a mile to fetch gas.

[Mike T.]

Re: Too hot at idle. with a different twist

John - You mentioned you get a vacuum reading of 13" at idle and that appears to be a bit lower than an L79 should produce. Maybe I missed it but has anyone asked what the altitude is at your location? Just wondering if you're far from sea level and that's why the 13" looks lower than it should be. I moved from about sea level in Northern California to 5K foot elevation here in Prescott AZ and all the cars seem to register about 3" less than they did back in California.