Too hot at idle. with a different twist
For the past year an overheating problem has been driving me nuts, and the usual suspects have been addressed with some success - BUT over heating at idle is still a problem. Here is the odd part the heat problem occurs when the hood is closed. Open the hood as little as a few inches (4" to 6") and the engine begins to cool and will idle forever with no temp problems UNTIL the hood is closed. Upon closing the hood the temp will creep up and usually about 225 the engine will vapor lock and die. The heat gauge is an NOS GM unit, I have verified temp with both an IR gun and a set of home made instruments with which I can measure outlet,inlet.ambient and oil temp. as well as battery voltage. The 210 mark on the temp gauge (1966) shows 210 when all of my gauges read within 1 degree of that metric. Ignition timing is spot on - and have experimented with a few degrees less and a few more. The vac is fully deployed at idle, the centrifugal is working. Have tried the stock fan (5 blade, 25 degree angle) along with the correctly dated and proper fan clutch, a new Hayden clutch, a 7 blade 34 degree blade for a 65 AC car, a clutch eliminator, two thermostats - both 180. One was a stant, the other was a "fail safe". China was the source of the stant, Isreal was the source of the Fail Safe. SOO. has anyone even run into this problem? Will gladly any questions you may have! I am desperate to make this overheating at idle go away! Many details left out of this narrative, but ask and they will gladly be provided. Please help make this crazy overheating problem go away.
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Re: Too hot at idle. with a different twist
Has your engine been bored out ? If so, by how much ?
Has your radiator been pressure tested ? How old is it ? Is it the correct material ?
What radiator cap are you running ? -
Re: Too hot at idle. with a different twist
Hi John,
Sounds frustrating! I'll ask the first questions:
Which year / engine?
How many degrees of timing at idle?
What is idle RPM?
What is vacuum at idle?
What vacuum advance do you have and have you verified that it is working properly?
Have you verified the fan clutch tightens when it should?
JoeComment
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Re: Too hot at idle. with a different twist
Frank, I cannot answer that question. I will get a borescope soon and peek inside and see if the oversize stamp on top of the pistons can be read. The engine is fresh, I have put two thousand miles on it and probably not much before that.Comment
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Re: Too hot at idle. with a different twist
What year? Which engine? OE equivalent cam? Manual or automatic? AC, and was it on? Is it an original emission controlled CA car? What's the number stamped on the VAC bracket? What is the actual initial timing in degrees? Is the distributor original and to OE spec or modified? Radiator - OE, Dewitts replacement, aluminum, brass?
Most modern replacement fan clutches are "tuned" for a 195 degree thermostat, so the clutch doesn't tighten until radiator outlet air temp is higher than original clutches designed for a 180 thermostat.
At 225 coolant temp is the fan much stiffer than when cold?
DukeComment
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Re: Too hot at idle. with a different twist
Joe, the car in question is a 1966 conv, 350 HP. The ignition timing is set at 8 degrees, vacuum line not connected when set. The idle speed at this time is 970 with an electronic tach, or close to 900 with the factory mechanical unit. Have increased to 1200 and 1500 trying to cool engine but once the heat begins to rise when hood is closed it just doesn't want to come back down. The engine vacuum at idle is 13".I do not know the number on the VAC, but is fully deployed at idle. The clutch that came with the car showed signs of leaking although using a timing light showed it to be only slightly slower than the engine speed, which seems to typical. The Hayden replacement was purchased and tried, but no improvement. a fan clutch eliminator is not installed so there is no doubt about the fan speed being all it can be. At this time along with the eliminator is a 7 blade fan (reproduction) for a 1965 corvette with factory air conditioning. In addition to more blades it also has a steeper pitch. The fan positioning is very good, with the center of the blade rivets centered on the trailing edge of the fan shroud.Comment
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Re: Too hot at idle. with a different twist
Normal L-79 idle behavior is 14-15" @ 750 in neutral. If your engine is only pulling 13" @ 970 that indicates some other cam with more overlap. You may need to lift the dist. cap to see the VAC number, but it's important to know.
With 8 initial and 16 full vacuum total idle advance should be 24, but since the OE centrifugal starts at about 700, higher idle speed will cause a few degrees centrifugal. In any event total idle timing should be stable within a narrow range. Check with a timing light and report.
After extensive idling does idle speed decline slowly and then stall, or does it stall quickly from the 970 idle speed?
Also need answers to the other questions in my previous post.
DukeComment
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Re: Too hot at idle. with a different twist
Duke, 1966, 350 Hp (L79). four speed, 3:36 gear, does not have AC. It is a 49 State car with no emission controls. Do not know the number on the VAC The initial timing with VAC unhooked as 8 degrees, and advances off the timing marks as soon as the vacuum hose is connected to the distributor The distributor I believe to be OE spec, the tag shows it is proper for the engine but have not had it on a stroboscope to verify. The 195 setting on the clutch should not be an issue since there is now have a fan clutch eliminator installed. I suspect the original clutch is not up to the job, and thus the Hayden was installed. The Hayden (new from NAPA) made no appreciable difference with either the original correct fan or the reproduction 7 blade AC fan. At 225 the Hayden clutch seemed more "stiff" than the original GM, but the problem persisted with either.Comment
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Re: Too hot at idle. with a different twist
Per my prior post we need the number on the VAC and total idle advance.
Also need requested info on the installed radiator. Original? Dewitts repro or something else?
After extensive idling and the temp gets to 220 measure exh. manifold temp along the lengths and report the range. Hold the gun close to the manifolds. IR guns typically measure a 4:1 cone, so if it's too far away and picks up cooler background radiation it will average the temperature, which will be lower than actual manifold surface temp.
DukeComment
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Re: Too hot at idle. with a different twist
Duke, out daughter and her family is here for Mothers day so unable to determine the Vacuum can number until Monday. Will give you a full rundown then. But Looking at my notes on this project, you may find this interesting. With an ambient temp of 85. the engine was at idle (750 RPM) for a little over one hour with a water temp of 185. The hood was closed and the temp began to climb and within 10 minutes was at 217. Test aborted since from past experience vapor lock begins at 225. When "Terminal Temperature" is reached the engine begins to stumble and within seconds sputters and expires. After cooking (mostly over night) one must crank an abnormal amount of time and pump the accelerator several times in order to restart. On one occasion I used the car to run an errand letting it run while I ducked in a parts store. Upon returning only a few minutes later it was just starting to stumble so I began to drive home (8 miles) and the first two miles were very "iffy" with stumbles and worrisome pauses. Never did quit and unsettling. Oh, and the intake to water pump is now plugged since Thursday . This seemed to help cool or prolong the temp rise, but still would climb when the hood was closed. Also tried restricting the heater hose coming from the intake to force more water through the radiator but no change at all from this, at least with the hood closed.Comment
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Re: Too hot at idle. with a different twist
Duke, the radiator is a Dewitts Stacked unit. I think it has been installed four years. I have drained and refilled with new Zerex premixed (the green variety) three or four times in the last year. Each time the liquid was clear and appeared to have no rust. Also tried distilled water and Water Wetter only (still had some residual anti freeze present of course. with little or no change. Will get manifolds temp readings Monday after our company leaves and report findingsComment
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Re: Too hot at idle. with a different twist
Well -- don't get talked into "re-clocking" the thermostatic spring on the fan clutch to have it engage sooner - that is a myth....
You can contact KirkConnell Corvettes - the top restorer of original fan clutches to hear personally why that "trick" is bogus...
They will demonstrate on a fan clutch "cutaway" why that doesn't work at any NCRS event they attend if you ask...Comment
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Re: Too hot at idle. with a different twist
How about a picture or two? Seems like with the hood closed it is creating some kind of vacuum and not letting air flow. How far from the radiator is the fan? Is the complete shroud in place? How long is the fan clutch eliminator? Do you have the correct pulleys?Comment
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Re: Too hot at idle. with a different twist
Terry, I am too stupid to post images on this forum. Will be more than happy to send images to you by phone if you are interested - maybe you can post them and that would be great. My phone is 217 971 7183 or email at j.w.murphy@comcast.net .Comment
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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*.Comment
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