OVERHEATING ISSUE

[VETTE1966]

I have a 66 convertible 327/300, no air or much else dragging on the engine. The car's temperature on hotter days (85++) tends to creep up whenever I am at a light for more than 30 seconds. It backs down a little when it start driving again but over a half-hour to hour of this city driving, the needle starts to push the 210 mark. And if I stop for a slightly longer time after that (like waiting in a line to park at a car show) it'll hit 220 +.

I have replaced the radiator, fan clutch, all hoses and have a new 180 thermostat (which I have tested) in the car. The gauge is OK as I have a laser tester that I tested the temp by the thermostat housing. While I know the car is old and the hot weather is hard on it, the temp seems to creep up faster than one would expect in traffic--I can't keep my eye off the gauge. It seems other C-2 owner's I talk to don't heat up so fast unless they're in a big traffic jam.

So am I missing something here...or do I just learn to live this and be thankful i don't drive too far or long on hot days? Thanks.

 

[67HEAVEN]

You've done plenty of good things already. I assume that when the rad was switched out, you (or they) flushed the engine too.

There's a possibility that, although new, the fan clutch may not be operating correctly.

 

[JimVette]

I had the same problem years ago on my '66 327/350. Mine started after I replaced the clutch. I suspected the clutch was defected. After I had the fly wheel resurfaced and replaced the clutch again it never ran over 200 even on the hottest days in traffic.

 

[JohnZ]

What kind of "new" radiator do you have?

Is the shroud in place?

What's your initial (base) timing, and have you verified the correct operation of the vacuum advance unit?

 

[VETTE1966]

THANKS for the insight; It's a perplexing problem as I had a good mechanic friend check out my water pump and clutch and they're OK. My Radiator was a new Dewitts correct aluminum replacement bought 2 years ago. The shroud is in place and the vacuum advance was replaced last spring.

I don't want to have the motor torn down to clean out whatever 40 year old gunk is there so I'm thinking I'm going to try to generate more airflow thru the radiator. I just replaced the fan with one with six blades (vs. five) and a steeper pitch to see what that does. We'll see--thanks again.

 

[Kid_Again]

i don't think it will do anything....

JohnZ's advice about ignition timing is right on....seen his advice work on a couple of cars....i bet it's either timed incorrectly, you have the wrong vacuum can or the advance mechanism sticks

 

[VAroute66]

I had the same aggravating problem with my '66 327/300, and it was the fan clutch. After you check your timing, and although you said you checked/replaced your fan clutch, make sure that when you shut your engine down, it continues to spin only for a couple of turns. If it keeps spinning it is bad. This helped fix my problem, but soon after I also found that my water pump was bad. If you change your water pump, replace it with a stock pump. I replaced mine with a high flow design and although my engine stays at about 180, I have a strange fuel vapor lock issue. How old is your water pump? Good Luck.

v/r

Dan

 

[JohnZ]

My Radiator was a new Dewitts correct aluminum replacement bought 2 years ago. The shroud is in place and the vacuum advance was replaced last spring.

OK, we know you don't have a radiator problem, you have a low-speed airflow problem, possibly aggravated by ignition timing. The fan change may help, but you also want to make sure your timing and vacuum advance are set up correctly.

Your base timing (with the vacuum advance disconnected) should be between 8*-12*, and the vacuum advance can should be connected to a full manifold vacuum source and fully-deployed at normal idle so it adds another 15* of timing at idle - this is VERY important for idle and slow traffic cooling. The vacuum advance unit must be matched to the engine's idle vacuum characteristics, and must be chosen so it's fully-deployed at least 2" Hg. BELOW your normal idle vacuum. Tell us what your idle vacuum is and we can tell you the advance unit you need.

 

[Viet Nam Vett]

OK, we know you don't have a radiator problem, you have a low-speed airflow problem, possibly aggravated by ignition timing. The fan change may help, but you also want to make sure your timing and vacuum advance are set up correctly.

Your base timing (with the vacuum advance disconnected) should be between 8*-12*, and the vacuum advance can should be connected to a full manifold vacuum source and fully-deployed at normal idle so it adds another 15* of timing at idle - this is VERY important for idle and slow traffic cooling. The vacuum advance unit must be matched to the engine's idle vacuum characteristics, and must be chosen so it's fully-deployed at least 2" Hg. BELOW your normal idle vacuum. Tell us what your idle vacuum is and we can tell you the advance unit you need.

What John Z has posted here is Very Very Important..!! Do yourself a favor and check thses items out. I'm sure you will find that this will help. If your motor is running retarded at idol in trafic on high temp days..You will over heat..!

Good luck on your cooling quest..

 

[vigman]

Engine timing 101

Just to be SURE I get this
( since it's been a while that Vac has controlled timing on my rides).

Initial timing 8-12 deg BTDC right? W/O Vac advance hooked & plugged
( or whatever the book states ) Let's assume 10 degrees BTDC

Hook up the advance.. you should see a additional 15 degrees of timing change?.. I assume this will push things ADVANCE so now were at 25 degrees of total timing @ idle. Or 15 degrees ATDC@ idle

The vac source is ported vacumme BELOW throttle plates...

So when you ROMP on it.. the timing will move BACK twds BTDC ( which in my mind is advance.. because the spark happens earlier ).

So how does mechanical play in.....?

In other words... as I rev the motor ( using the timing light ).. the timing pointer should move BACK twds BTDC... not FWD ATDC as the RPM climbs
( RIGHT?)

Haven't had to deal with this for a bit.. want to make sure I get it...

Thanks
Vig~

 

[Viet Nam Vett]

Just to be SURE I get this
( since it's been a while that Vac has controlled timing on my rides).

Initial timing 8-12 deg BTDC right? W/O Vac advance hooked & plugged
( or whatever the book states ) Let's assume 10 degrees BTDC

Hook up the advance.. you should see a additional 15 degrees of timing change?.. I assume this will push things ADVANCE so now were at 25 degrees of total timing @ idle. Or 15 degrees ATDC@ idle

The vac source is ported vacumme BELOW throttle plates...

So when you ROMP on it.. the timing will move BACK twds BTDC ( which in my mind is advance.. because the spark happens earlier ).

So how does mechanical play in.....?

In other words... as I rev the motor ( using the timing light ).. the timing pointer should move BACK twds BTDC... not FWD ATDC as the RPM climbs
( RIGHT?)

Haven't had to deal with this for a bit.. want to make sure I get it...

Thanks
Vig~

Heh Vig,
Go to this Link....

Barry K has put alot of info together on his web site from the experts like John Z and Others..

Scroll down to the ingnition section and you will find tech articals on timing and Vacuum set ups...



http://www.lbfun.com/Corvette/Tech/vettetech.html

 

[JohnZ]

Scroll down to the ingnition section and you will find tech articals on timing and Vacuum set ups...



http://www.lbfun.com/Corvette/Tech/vettetech.html

Scroll down to "Timing 101.pdf" - right-click to download it, left-click to read it.

 

[vigman]

Ok I read it.....

My behaivor is different...

1) The carb is a Holley and seems to have only vac port.. which only has vac when the throttle plates open up a bit ~1000 rpm ( 750 single pumper Vac secondaries).

2) I have a REALLY SMALL Harmonic balancer which is MILES AWAY from a timing pointer.. it looks like the initial is set to 8 deg BTDC.. disconnecting the vac advance has no effect @ idle 600rpm. and the timing tab is welded to the front of the chain cover ( after market chrome jobby ).

3) When winging the motor.. it looks like about 30+ degrees of total advance I do not have a delay timing light....

4) I opened up the distrib and found a very thin piece of plastic ( round flat ) like a sticker internal of the distrib.. pulled that out.. checked the mechanical adv. Now it moves freely ( Petronics module & MSD blaster).I also checked with a vac gauge that the vac advance works.. and it does.
Leaving the Vac hose off the carb.. the mechanical works, now returning SMOOTHLY to base timing.

5) I dialed a few more degrees of retard in it...


The result
The car had a problem misfiring/backfiring in a off idle slow acceleration.
Still has it.. maybe a bit worse now.

The car idles round 180 deg.

So If I understand the post ( and not meaning to hijack it )

The Vac advance is not hooked correctly and should be hooked to BELOW throttle plates to manifold vac.

Still confused though.

Vig~

 

[Rowdy1]

Shopvac?

I have nothing, no nothing. A BIG Victor Jr. intake with a massive opening, ONE big hole, no issues with street driving, can idle around all day, take it out on the "big" road, smash it and pull 7,000 plus in every gear. I ran the original plugs in it from break in to just last year and never had to replace one, 13,000 miles. Timing mark, pointer? What's that, I have ears................

 

[JohnZ]

So If I understand the post ( and not meaning to hijack it )

The Vac advance is not hooked correctly and should be hooked to BELOW throttle plates to manifold vac. Vig~

That's correct. Dunno which Holley you have, but if it has a vacuum diaphragm on the passenger side (choke pull-off), the hose that feeds it from the front of the baseplate is full manifold vacuum (below the throttle plates); tee into that hose for your vacuum advance line.

 

[vigman]

Thanks John

Well... the pass side does have a vac port.. but it doesn't pull vac till 1000 rpm.. and here in So Cal.. I don't have a choke... all gone.

So I'll have to do some sniffing where I can tap in....

It's starting to make sence


Vig~

 

[JohnZ]

Try the FRONT of the baseplate - just about every Holley has a full manifold vacuum port there, on an angle pointing toward the passenger side of the engine.