Last fall I traded my 66 convertible for a 68 L89 coupe that has been well restored. It's the first 68 I've had as well as a 427/435 L89 and a 411 rear end. I've been through most all weather temperatures in the last 9 months and none seem to affect the way the engine heats up, driving or idle. I'm experiencing a slow rise to high temperatures where the gauge easily reaches past 210 but peaks somewhere before the critical 230-240+ shut down stage. For one reason or another, the "experienced" I have spoken to have told me to expect it, that it will run hot. I did have the original radiator cleaned (it works well), adjusted all belts, checked the fan clutch, changed to a new 180 thermostat, (basically did the other "obvious" things) and in addition reset the timing to the correct 68 spec of 4 BTDC, from where it was purposely set at 10 BTDC by the previous owner. I am curious about the TI distributor and how it may be affecting from what all else appears to be an original, numbers matching set-up. The previous owner did tell me two things: 1. that he changed the jets in the center carb for more performance, and 2. that the current TI distributor is from a 66. Are the specs for this distributor the same as they should be for a 68 (L89) TI distributor and if not should my timing, etc, be set for the 66 or 68 specs? Does the year-make of the TI amp need to be the same as the year-make of the TI distributor? Could something like advance and timing, with this circumstance, be affecting the "over-heating" temps I have been experiencing, or do I need to quit worrying and be comfortable that this big block with a 411 runs hot? I'd like to know answers to all those questions as well as the advice of what diagnosis or adjustments I need to make, sit, or take. Thanks in advance.
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Tom----
There are some POSSIBLE configuration differences between 66 and 68 TI ignition systems. From 1964 through early 1968, the TI amplifier used a seperate, plug-in type of wiring harness. After early 1968, the design changed to an integral "pigtail" type harness which attached to another harness. However, the basic TI system remained unchanged. There may be some centrifugal/vacuum advance characteristics differences between the 66 distributor, depending upon which part number it is, and the distributor which is supposed to reside on your L-89. However, I seriously doubt that these differences would account for any of your overheating problems. I would definitely set the initial timing to the specs for your 68 L-89 which is 4 degrees BTDC.In Appreciation of John Hinckley -
Re: 66/68 TI Distributor, Overheating, Carbureatio
Tom----
There are some POSSIBLE configuration differences between 66 and 68 TI ignition systems. From 1964 through early 1968, the TI amplifier used a seperate, plug-in type of wiring harness. After early 1968, the design changed to an integral "pigtail" type harness which attached to another harness. However, the basic TI system remained unchanged. There may be some centrifugal/vacuum advance characteristics differences between the 66 distributor, depending upon which part number it is, and the distributor which is supposed to reside on your L-89. However, I seriously doubt that these differences would account for any of your overheating problems. I would definitely set the initial timing to the specs for your 68 L-89 which is 4 degrees BTDC.In Appreciation of John HinckleyComment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Thanks Joe. The car is an early 68 (Dec 67) and there are no modifications to the wiring. The engine runs well as is, not rough, and I'm trying to make sure that things like the 66 TI distributor are not there to eventually mess it up, even in the littlest bit. I still have suspicions about the jets in the center carb since supposedly they are bigger and it seems to me it really uses the fuel, when in reality it may or may not be the case (it could just be me). Buuuuut, that keeps me guessing if maybe there's more fuel or fuel-in-the-air mixture burning to keep my engine temp hot. I do run a 109 octane fuel (the real stuff) in it. And I still wonder about the "over-heating": IS it "normal". There's more I'd still like to hear if you or someone else picks up on it.Comment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Thanks Joe. The car is an early 68 (Dec 67) and there are no modifications to the wiring. The engine runs well as is, not rough, and I'm trying to make sure that things like the 66 TI distributor are not there to eventually mess it up, even in the littlest bit. I still have suspicions about the jets in the center carb since supposedly they are bigger and it seems to me it really uses the fuel, when in reality it may or may not be the case (it could just be me). Buuuuut, that keeps me guessing if maybe there's more fuel or fuel-in-the-air mixture burning to keep my engine temp hot. I do run a 109 octane fuel (the real stuff) in it. And I still wonder about the "over-heating": IS it "normal". There's more I'd still like to hear if you or someone else picks up on it.Comment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Tom, I would also check to confirm that the reading on the gauge is really the actual temperature. One common problem I've seen is the temperature sender. If it is not an original unit it is probably out of calibration. One of the past issues of the Restorer has a very good article about the senders and the corresponding resistance that they should have at various temperatures. Good luck. Let us know how you make out. MarkComment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Tom, I would also check to confirm that the reading on the gauge is really the actual temperature. One common problem I've seen is the temperature sender. If it is not an original unit it is probably out of calibration. One of the past issues of the Restorer has a very good article about the senders and the corresponding resistance that they should have at various temperatures. Good luck. Let us know how you make out. MarkComment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Tom, I bought a 69 435 coupe last fall and the owner said it always ran hot. He had added an electric fan that he would turn on manually whenever the temp got too high. It had no thermostat, just a restrictor plate. Anyway, I got rid of the fan, the restrictor plate, the new GM water pump an a useless fan clutch, which I think was the major part of the problem. Put in a new fan clutch, a Robertshaw 160 thermostat,a Flowcooler waterpump and the temp gage has yet to reach the 210 mark and normally runs between the first and second hashes. The cure was recommended by Steve Cataldo in one of last years Restorers. The Flowcooler looks just like the original but it won't be missed by a judge. But that temp gage reading really gives me peace of mind.Comment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
Tom, I bought a 69 435 coupe last fall and the owner said it always ran hot. He had added an electric fan that he would turn on manually whenever the temp got too high. It had no thermostat, just a restrictor plate. Anyway, I got rid of the fan, the restrictor plate, the new GM water pump an a useless fan clutch, which I think was the major part of the problem. Put in a new fan clutch, a Robertshaw 160 thermostat,a Flowcooler waterpump and the temp gage has yet to reach the 210 mark and normally runs between the first and second hashes. The cure was recommended by Steve Cataldo in one of last years Restorers. The Flowcooler looks just like the original but it won't be missed by a judge. But that temp gage reading really gives me peace of mind.Comment
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Some easy help is possible
GM changed the shroud design by '69 to help cool the big block Corvettes more efficiently. You probably have one of those communist round metal shrouds on your early car. They don't work well at all compared to the '69 type full coverage shroud.
Changing shrouds won't get you all the way home, however. I support the above advice about checking the sending unit accuracy. If a mechanical gauge says you really are running at 230-240 degrees, then your problem is probably in your heads.Comment
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Some easy help is possible
GM changed the shroud design by '69 to help cool the big block Corvettes more efficiently. You probably have one of those communist round metal shrouds on your early car. They don't work well at all compared to the '69 type full coverage shroud.
Changing shrouds won't get you all the way home, however. I support the above advice about checking the sending unit accuracy. If a mechanical gauge says you really are running at 230-240 degrees, then your problem is probably in your heads.Comment
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Re: 66/68 Overheating, Carburation
Tom, if all else checks out, why not do the easy work and change the center carb jets back to # 63's and try it out ? Verify the power valve while you're there. Have you read the sparkplug color ? (they should be AC43XL, not 43N's) Remember to let engine cool considerably before pulling plugs from aluminum heads. Anyway, the center carb is the economy unit; the performance comes from the end carbs.
As Jerry says, the problem may end up being in the heads. Assuming you have the 842's, you should have the correct head gasket for aluminum heads, with cooling hole patterns and sizes that match the head and block passages.
If anything, L89's should run cooler than iron-head L71's, because of the better heat transfer of aluminum, assuming the radiator, clutch fan and shrouding are not limiting. For sure, they should have less tendancy to "puke" coolant on shut-down, as less heat is stored in these heads.Comment
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Re: 66/68 Overheating, Carburation
Tom, if all else checks out, why not do the easy work and change the center carb jets back to # 63's and try it out ? Verify the power valve while you're there. Have you read the sparkplug color ? (they should be AC43XL, not 43N's) Remember to let engine cool considerably before pulling plugs from aluminum heads. Anyway, the center carb is the economy unit; the performance comes from the end carbs.
As Jerry says, the problem may end up being in the heads. Assuming you have the 842's, you should have the correct head gasket for aluminum heads, with cooling hole patterns and sizes that match the head and block passages.
If anything, L89's should run cooler than iron-head L71's, because of the better heat transfer of aluminum, assuming the radiator, clutch fan and shrouding are not limiting. For sure, they should have less tendancy to "puke" coolant on shut-down, as less heat is stored in these heads.Comment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
There is a lot in the archieves about 'overheating' and 'elevated' temp Corvettes branded as 'hot' running. Many respondants have given you solid advice on what might be wrong and alternatives to correct that are valid. My advice is to begin with SCIENCE instead of kneejerk.
This isn't a slap, it's a theme I see repeatedly. All starts with the owner looking at the temp gauge and taking its display reading for gospel. The place to start is by verifying the actual engine temp vs. what the gauge reads. If you don't take this step, you can spend needless $$$ and time chasing 'ghosts'....
Temp guages in Corvettes (and other GM cars of the era) are purposely vauge (imprecise graduations on face/scale). I believe this is because the allowable accuracy of the AC temp sender varied that much from unit to unit. Plus, there were running changes in the construction of temp senders (how they were sealed, whether the internal body of the transducer was oil filled or not, Etc.). If the temp sender body is breached, coolant can enter and eat at the ohmic contact integrity of the transducer causing its T/R curve to shift.
So, there are many considerations here, but my suggestion is to first verify the accuracy of the temp sensing system in your car vs. reality. If you find it's off (my bet), there are a number of solution paths. I just installed one of the first off-the-line reconditioned original AC temp senders from Fred Oliva at Vintage Automotive Research and BINGO I got a 10 degree difference (better/more accurate) in the reading of my '71 SB.
This is an interesting new service. Fred is taking original AC senders (marked on barrel), dissecting them, installing hand calibrated new tranducers, resealing the assy, refurbishing the exterior cosmetics and pressure/temp/water integrity verifying the final product. Good stuff!Comment
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Re: 66/68 TI Distributor, Overheating, Carbureatio
There is a lot in the archieves about 'overheating' and 'elevated' temp Corvettes branded as 'hot' running. Many respondants have given you solid advice on what might be wrong and alternatives to correct that are valid. My advice is to begin with SCIENCE instead of kneejerk.
This isn't a slap, it's a theme I see repeatedly. All starts with the owner looking at the temp gauge and taking its display reading for gospel. The place to start is by verifying the actual engine temp vs. what the gauge reads. If you don't take this step, you can spend needless $$$ and time chasing 'ghosts'....
Temp guages in Corvettes (and other GM cars of the era) are purposely vauge (imprecise graduations on face/scale). I believe this is because the allowable accuracy of the AC temp sender varied that much from unit to unit. Plus, there were running changes in the construction of temp senders (how they were sealed, whether the internal body of the transducer was oil filled or not, Etc.). If the temp sender body is breached, coolant can enter and eat at the ohmic contact integrity of the transducer causing its T/R curve to shift.
So, there are many considerations here, but my suggestion is to first verify the accuracy of the temp sensing system in your car vs. reality. If you find it's off (my bet), there are a number of solution paths. I just installed one of the first off-the-line reconditioned original AC temp senders from Fred Oliva at Vintage Automotive Research and BINGO I got a 10 degree difference (better/more accurate) in the reading of my '71 SB.
This is an interesting new service. Fred is taking original AC senders (marked on barrel), dissecting them, installing hand calibrated new tranducers, resealing the assy, refurbishing the exterior cosmetics and pressure/temp/water integrity verifying the final product. Good stuff!Comment
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