1963 327/340 running hot

**Bob R.** · August 5, 2020, 01:31 PM

Re: 1963 327/340 running hot

There are many reasons why your car would run hot and I'm sure you will get other responses but a few things to check: What is your timing set at, how old is your radiator, what are you using for fuel, is the fan clutch working properly, is the antifreeze at proper level, are all the seals installed on the fan shroud, when the engine work was done did they bore out the engine. These cars will run very hot idling for any period of time and are not well suited for a parade.

**Bob A.** · August 5, 2020, 01:57 PM

Re: 1963 327/340 running hot

Originally posted by Bob Rosenblatt (38164)

There are many reasons why your car would run hot and I'm sure you will get other responses but a few things to check: What is your timing set at, how old is your radiator, what are you using for fuel, is the fan clutch working properly, is the antifreeze at proper level, are all the seals installed on the fan shroud, when the engine work was done did they bore out the engine. These cars will run very hot idling for any period of time and are not well suited for a parade.

Thx Bob.
Radiator is NOS 6-7 years old in perfect condition and has been tested, using 93 octane, fan clutch working properly, antifreeze is at proper level, seals have been installed around shroud, two-three cylinders were bored but slightly. I'll advise on the timing.

Is 200 degrees normal for a 327/340 on the open road at 90 degree ambient temperatures and a flat terrain?

Much appreciated! Bob

**Bob A.** · August 5, 2020, 02:09 PM

Re: 1963 327/340 running hot

Bob,
Engine was bored .060 over and timing was set at 10 degrees.
Bob

**Stephen L.** · August 5, 2020, 02:14 PM

Re: 1963 327/340 running hot

Did the car run at elevated temps BEFORE rebuild? Was the block water jacket boiled out during rebuild. Was the radiator flushed after rebuild? Was the water pump replaced?

**Joe L.** · August 5, 2020, 02:55 PM

Re: 1963 327/340 running hot

Originally posted by Bob Aquilino (32465)

Thx Bob.
Radiator is NOS 6-7 years old in perfect condition and has been tested, using 93 octane, fan clutch working properly, antifreeze is at proper level, seals have been installed around shroud, two-three cylinders were bored but slightly. I'll advise on the timing.

Is 200 degrees normal for a 327/340 on the open road at 90 degree ambient temperatures and a flat terrain?

Much appreciated! Bob

Bob------

I would say that 200 degrees running in 90 degree ambient is "on the edge of normalcy"---maybe 5 to 10 degrees higher than I would expect. My expectation would be that this 5-10 degree higher-than-previous operating temperature is a result of two things. First, is that it's a newly rebuilt engine and will have somewhat higher internal friction until it "wears in". Second, is the 60 overbore. Why did it need a 60 overbore? Did it have previous overbores and/or a LOT of taper?

**Edward J.** · August 5, 2020, 03:13 PM

Re: 1963 327/340 running hot

Bob, I would not lose sleep over it, the outside temp has been really hot lately everywhere, so figure about an added 10 degrees .sounds like you have the engine spec.s set. Temp. Is technically not overheating.drive it some more and see how the gauge does as the temp drops some.

**Bob A.** · August 5, 2020, 04:23 PM

Re: 1963 327/340 running hot

Thx Ed.

The temp gauge was running 200-210 prior to the recent heat wave although the ambient temperature at the time was around 90 degrees. Is it unusual for a 327/340 to run at 200-210 degrees under normal driving conditions?

Bob

**Bob A.** · August 5, 2020, 04:31 PM

Re: 1963 327/340 running hot

Thx Steve,

The car did not run at elevated temps prior to the rebuild. The block was completely cleaned prior to matching and assembly. The radiator was flushed and pressurized. The water pump was not replaced. Didn't see a reason for it. I guess the question is, is 200 degrees in the acceptable range for a 327/340 and can that engine sit at idle without puking?

**Mike T.** · August 5, 2020, 04:33 PM

Re: 1963 327/340 running hot

Bob - In your first post, you mentioned the 'sending unit and gauge' have been calibrated. The gauge I understand but what exactly did someone do to 'calibrate' the sending unit? A number of over the counter temp sending units have been the cause of abnormal gauge indications. One that is close to accurate is the Wells TU-5 that is sold from various vendors and it's not perfect either. As Edward mentioned, we're all seeing elevated temps this time of year but wondering if another reason for the higher readings is due to the sending unit and gauge being replaced and worked over. Maybe your engine was always running a bit on the high side temp-wise but the old sending unit and gauge just didn't properly indicate it.
As to the question you've been asking..."Is it unusual for a 327/340 to run at the 200-210 degree range", I'd say yes. One other thing to ask, will it continue to rise beyond the 200-210 or is it fairly steady at that point?

**Mark E.** · August 5, 2020, 04:37 PM

Re: 1963 327/340 running hot

What temperature thermostat is installed? If 195, running a few degrees above its setting is normal.

A lot can be learned by watching the temp gauge. From a cold start, does it steadily climb to thermostat opening, then oscillate around that temp as the thermostat cycles? In this case, cooling system capacity is greater than heat load.

A few minutes after thermostat opening, does the temperature continue to climb then settle at a higher temperature but not overheat? In this case, cooling system capacity is on the edge of being able to handle heat load. In this situation, when does the high temperature occur? Idle? Cruising speed? This can give clues (e.g. not enough airflow at idle, retarded timing at cruise RPM, etc.).

**Bob A.** · August 5, 2020, 04:48 PM

Re: 1963 327/340 running hot

Thx Mike,

You make a great point. It could have been running high prior to the rebuild and I wouldn't have known it. What I do know it that the temp gauge is the same as the head temp when checked with an IR gun. The readings match.
I will look into the gauge-sending unit calibration, don't know. On the road, it stays steady at the 200-210 max degree point. Sitting at idle, it continues to rise. It has not puked sitting at idle but if I let it, it would.

**Bob A.** · August 5, 2020, 05:03 PM

Re: 1963 327/340 running hot

Mark,

Good insights! It has a 160 thermostat. With the 160 and the gauge/head temps running at 200, tells me cooling capacity is lower than demand.
I'll will follow your suggestions in watching the temp gauge and advise. All good points on observing the timing of thermostat opening and temp gauge rising. The temp rises when air flow subsides at a stand still.

**Dan H.** · August 5, 2020, 06:18 PM

Re: 1963 327/340 running hot

Bob, did you rebuild the distributor? New VAC perhaps. Check the function of the advance to make sure it is correct. I had a repro VAC go bad on me, over heated etc. Also you might swap the temp sending unit just to be safe.
Dan

**Timothy B.** · August 5, 2020, 06:36 PM

Re: 1963 327/340 running hot

Bob,

A few thoughts, is the radiator cap holding 13lb pressure, if not the system will overflow when hot. The stock 340hp distributor has 24* centrifugal advance so you want to run approx 12-14* initial plus a vacuum advance the provides another 15* all pulled in at idle speed. This will yield a total idle timing approx 27-29*.

My engine has a .060 overbore also and runs hotter like you describe but I don't think it will hurt anything provided things I mentioned above are in good working order. I probably would not use it in a parade, these corvettes have a very confined engine compartment and they don't vent heat as good as some other cars.

Try to pop the hood and let some heat out if you get in a situation where the gauge gets near 210.

1963 327/340 running hot

1963 327/340 running hot

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