Years ago I had my 1965 327/365 engine rebuilt. I spun a bearing. That's what happens when you drain the oil and replace the filter but don't refill the oil in the same day. Yeah, the memory doesn't get better with age. The shop said they shot peened the pistons to expand the skirts and replaced the bearings and rings. After that the engine would run cool as long as you were moving, but let it idle and the temp would climb quickly and boil over. No changes to the radiator, probably the same water pump, but I did change cams. I never figured out what was wrong, I sold the problem. Any ideas? Now I've bought a Ralley 350 Olds with the same problem. Tried different radiators, fans and shrouds no effect. This engine seems to have a very radical cam (loop and no vacumn at idea, probable the W31. Can a cam effect cooling as I describe?
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Re: Over heating sbc
Robert -
I've never seen a cam cause or cure a cooling problem, but I haven't seen them all. Idle cooling issues are usually airflow-related, and are aggravated by inoperative or improperly-connected vacuum advance units. -
Re: Over heating sbc
Robert,
I agree with John, the camshaft makes such low idle vacuum that the advance control does not work, the total idle timing is just the inital setting. Hot cams like rich mixtures and that can also contribute to hot idle condition.Comment
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Re: Over heating sbc
Had this engine ever been overbored?
Peening, and "knurling" (an anacronism from a past era), sounds like a half-azzed answer for needing to hone the bores...a lot. If the bores were that rough, it probably should have been overbored to the next available piston size. However...that is a lot of additional expense, and stock piston sizes, along with casting wall thickness, set the limits for overboring.
My old engine rebuilder always preferred boring to the next size...but, he never rested comfortably until one of his overbored engines had run without overheating. It didn't matter if it was the minimum overbore or the maximum available. FWIW...this likely has no application to this problem.Comment
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Re: Over heating sbc
Robert,
I'm not a mechanic, but I have been dealing with an issue with my engine that turned out to be timing related. After a lot of research online and with the help of NCRS members, I learned that aggressive cams require more distributor timing. Your total mechanical timing (with the vacuum advance disconnected and the line plugged) should be 34 to 36 degrees all in at 3,000 RPM. With the vacuum can connected, total timing should be between 50 to 52 degrees. If your initial timing at idle is higher than 20 degrees when connected to the carb manifold vacuum port, you can connect to ported vacuum which won't add any additional vacuum advance timing at idle. Not only will you get some additional kick in the seat of your pants and perhaps better highway MPG's, the advanced timing will have your engine running cooler. I didn't have a cooling problem, but learned about this from my research - and I have noticed that my engine does run cooler than it did before. Make sure that you don't get any "pinging" when you go out for a drive as that is damaging to the engine. If so, retard the timing 2 degrees at a time until the pinging stops. Those that know more than me are welcome to chime in if you think I got something wrong
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Roger (50141)Comment
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Re: Over heating sbc
You need to do more research - you got it wrong. Most "mechanics" don't understand it either. They may understand (vaguely) the spark advance requirement for maximum wide open throttle power, but they are usually clueless when it comes to understanding the requirements for a SPARK ADVANCE MAP that covers the entire engine operating spectrum including idle and part throttle operation across the rev range.
Vintage Corvette engines need TOTAL IDLE SPARK ADVANCE in the low 20s to low 30s degrees range. This is usually achieved with the sum of initial advance and full vacuum advance with a vacuum advance control that complies with the TWO-INCH RULE connected to a full time vacuum source .
Low overlap cams can live at the bottom to mid-point of the above range, and high overlap cams need the mid to upper portion of the range. Failure to get total idle spark advance in the proper range can cause high EGT, which tranfers heat to the cooling system, which can result in high idle and low speed operating temperatures.
All the whys and wherefores are on the Web, particularly in a paper by Lars Grimsrud with an add-on article by me. (You should easily find it with a Google search.)
Total WOT timing - the sum of initial plus full centrifugal should be in as soon as possible, but may be limited by detonation. The "3000 RPM" is just a beginning guideline, and measuring at this speed may yield erroneous results because some OE centrifugal curves are not all in until as high as 5100 revs. Each individual engine can only be optimized with road testing.
An article in a recent Corvette Restorer issue reported that dyno testing of a vintage 327 yielded best across-the-range torque/power with 38 degrees total WOT timing and also explained the road/dyno test procedure used to optimize the fuel and spark advance maps for best fuel economy and best detonation-free torque/power from off idle to peak revs.
Ported vacuum advance was necessary for early emission control. It resulted in poorer throttle response and lowered fuel economy, but that was a price that had to be paid to meet emission requirements.
DukeComment
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Re: Over heating sbc
Duke,
Let me start by saying that I respect your engineering knowledge when it comes to engines and realize that I don't know a fraction of what you know in this subject. However, I did extensive Internet research regarding my engine issue which was resolved by advancing the timing due to the "more aggressive" cam in my engine. I don't need to look up Lars' paper because it is on the top of my stack of printed documents already, and the final piece that helped resolve my problem. The paper below that is one written by John Hinkley. I don't know if it makes a difference, but in addition to the modified cam, Robert's engine is a 350, not a 327. Quoting Lars, "most GM V8's will produce peak power at WOT with 36-38 degrees of ignition timing. Peak fuel economy and driveability at cruise is achieved with about 52-54 degrees of advance. Best idle quality has a much wider range depending on cam & engine, but tends to be in the 12-24 degree range." He goes on to say, "radical cams often require quite a bit of advance at idle. An appropriately selected vacuum advance unit, plugged into manifold vacuum, can provide the needed extra timing at idle to allow a fair idle, while maintaining maximum mechanical timing at 36. You must select a vacuum advance control unit that pulls in all of the advance at a vacuum level 2 in. Hg below the manifold vacuum present at idle." Now for the main point of this thread and hopefully the answer to Robert's cooling issue. As Lars puts it, "advancing the timing at idle can assist in lowering engine temperatures. If you have an overheating problem at idle, and you have verified proper operation of your cooling system components, you can try running manifold vacuum to an appropriately selected vacuum advance unit as noted above. This will lower engine temps, but will also increase hydrocarbon emissions on emission-controlled vehicles. If, however, your engine idles best in the 12-16 degree range due to a mild cam, plug the vacuum advance control unit to a ported vacuum source to eliminate the vacuum signal at idle. You will still obtain the 36 degree WOT total, and you'll still have 52 at cruise." As you can see, I posted what I learned from Lars, John, and others. Lars not only put it all together for me in one neat paper, he was also communicated with me via e-mail and commended me for making the proper adjustments to my engine timing. Duke, I don't think that I previously stated anything that was wrong based on Lars' paper. However, I agree with you that "each individual engine can be optimized with road testing". Robert, I would suggest trying to set your timing per Lars' and Duke's specifications and see if that fixes your overheating problem. You can easily put your timing back to where it is now if that doesn't help. Let us know how it works out for you!
Good luck,
Roger (50141)Comment
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Re: Over heating sbc
there are rebuilt water bumps use a stamped steel impeller which does not curculate the water like the original cast iron one. there is a company that sells a brass "disk" that can be attached to the stamped steel impeller to improve the flow.Comment
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Re: Over heating sbc
There is one bad post here, but all of the rest is good advice. Most often, idle overtemp is caused by insufficient spark advance or airflow problems across the heat exchanger fins. Your engine is an Olds, so I can't address specific timing specifications. I can only suggest that your spark timing works in accordance with the Olds Shop Manual for your engine. ONLY if your Olds engine calls for ported vacuum feed to the advance cannister, then a changeover to full manifold vacuum will help also. I would NOT make this modification until AFTER you have fixed your problem, as it will serve to INCREASE your idle overtemp safety margin. Make sure that your fan clutch is working properly. Make sure that your fan/shroud configuration and orientation is as it should be per Olds technical specs. Be sure that any and all air baffles are in place between the radiator and shroud so that no bypass air leaks out before passing thru the radiator. Seek help from Oldsmobile experts rather than Corvette experts for the specifics as they apply to your engine specs and dimensions. I very much doubt that a water pump impeller issue is causing your problem. If insufficient coolant flow was indicated, then this would show up at steady road cruise speeds, as this is when the cooling system is at maximum steady state load.
One more very important fact: If your cylinder bores were improperly honed, or if the hone employed too coarse a grit stone, then extreme friction would result, causing overtemp which will become more apparent during prolonged idling.Comment
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Re: Over heating sbc
Would a front license tag have any effect on the pass thought of air to the radiator?Comment
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Re: Over heating sbc
Lars and I are usually on the same page (He's also an engineer.), but the following statement you made in the first post raises a caution flag.
"If your initial timing at idle is higher than 20 degrees when connected to the carb manifold vacuum port, you can connect to ported vacuum which won't add any additional vacuum advance timing at idle."
Do you really mean initial or should this be total idle timing? They are not the same thing. I suspect you may have misinterpreted what Lars was trying to say.
The maximum vacuum advance of pre-emission control Corvette engines was usually no more than 16 degrees, however, there is at least one exception I can think of, and that is the '64 or '65 250/300 HP engines that had a 20 or 24 degree VAC. This was a one year anomaly and Chevrolet went back to a a 16 degree VAC for the '66 300 HP engine.
It took from '62 to '66 to get the 300 HP spark advance map somwhat optimized. Maximum centrifugal is 30 @ 5000, but the curve is non-linear and most is in by 3500, and 8 degrees initial yields 24 deg total idle timing, and 38 degrees total WOT timing above 5000.
The map can be optimized by bringing the centrifugal in quicker as we did with John McRae's Special 300 HP engine, and it produced better than expected low end torque.
1962 to 1964 mechanical lifter engines have a linear 24 degree centrifugal advance, so 14 degrees initial is necessary to achieve 38 total WOT advance, and this will produce 30 total idle advance, which is what these high overlap cam engines need. The '62-'63 SHP/FI engines had a lazy centrifugal - all in at 4600, and the 15.5" VAC didn't meet the Two-Inch Rule for the 340 HP engine. This was a moot point for the '63 FI engine because it had ported vacuum advance - another one year anomaly that Chevrolet fixed for 1964.
The '64-'65 SHP/FI centrifugal curve of 24 degrees is all in at 2350, and this represents and optimum curve if the engine does not detonate.
Things get more complicated if you are dealing with an emission controlled engine. The spark advance maps of these engines generally had short, lazy centrifugal curves with lazy, but high vacuum advance of 20-24 degrees at 18" or more vacuum. Again, these were emission control oriented spark advance maps with ported vacuum advance, and converting to full time vacuum advance REQUIRES installing a VAC with no more than about 16 degrees. If you don't change to a 16 degree VAC, you could end up with too much total idle timing, especially on base engines. Further optimization requires modifying the centrifugal by increasing the total and quickening the rate of advance. If the total centrifugal is only 20 then it would take 18 initial to achieve 38 total WOT advance, and if the VAC is 20 degrees ported and swapped to full time you end up with 38 total idle timing, which is way too much for a base engine or even SHP. This is probably what Lars was trying to get across.
Optimizing the spark advance map on an emission controlled engine is more work than on their pre-emission antecedents. It usually requires replacing the VAC and grinding out the slot in the weight base to increase total centrifugal. Pre-emission engines may only require different springs to bring the centrifugal in quicker.
As a general rule, base emission control engines can be optimized by starting with the '66 300 HP map, and SHP emission controlled engines can be optimized by starting with the '64-'65 SHP/FI map.
Your Olds engine will respond similarly since it is not that different, architecturally, from a Chevy Small Block. You didn't say what year, so I don't know if it's an emission controlled engine as originally built or not, and it sounds like it might have an aftermarket high overlap cam, but once you find out what you have, the guidelines for optimizing the spark advance map on a SB should apply.
The first thing that comes to mind, considering that it may have a higher than OE overlap cam, is that the VAC doesn't meet the Two-Inch Rule. Guys have been replacing OE low overlap cams with aftermarket high overlap cams for over fifty years, but few understand that such a change also requires modifying the spark advance map in order to maximize full rev range performance and prevent hot running at idle and low speed driving conditions.
You should be able to find the OE spark advance map in service literature. Then use a dial back timing light vacuum gage/pump to determine what you actually have. Then use what you now know about optimzing the spark advance map, and you will probably eliminate or mitigate the overheating as long as all your cooling system components are in good working order.
DukeComment
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Re: Over heating sbc
since you are posting about a olds engine does it have a water pump that is part of the timing gear cover? i remember some GM engines with this set up will over heat if a certain sheet metal baffle in not in there. not sure which GM engine this is. my reference to the sheet metal impeller is for chevy enginesComment
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