Hey guys I hope someone can help pleeeease. I have a 68 camaro 396, 4 speed, 12 bolt rear end. It has normally been running around 180f. I recently changed the intake and carb. The only thing I messed with was changing the thermostat and the timing. The thermostat is a 180f NAPA part and the timing is at 33 total advanced around 2500-2800rpm, at idle it is 12 advanced from what my friend said he set it at .

Now my car runs almost to the "H" if I let sit and idle for 10 minutes, but runs around 160-180f when I start driving it, what the heck can it be? All suggestions welcomed.

I installed another 180f thermostat and changed the coolant again 70%coolant, 30% water with water wetter added. Also changed sending unit.

Are you sure you installed the thermostat right-side-up?
Did the overheat start as soon as you changed the manifold and carb?

Thermostat is correct and yes this started after modifications, all I did was take out the high rise manifold and shot carb, and reinstalled the stock L78 manifold.

I would guess your initial timing is way retarding compared to how it was, or your vac advance is hooked up diferent (was manifold, now ported?)

Could be timing , and jetting on new carb.

I agree with the others...things I would check:

1) Timing incorrect...you may have inserted the distributor off by one tooth
2) Thermostat installed backwards...that will do it.
3) Incorrect seal between intake and heads, allowing exhaust gases into the cooling jackets.

Good luck,

Dave

Hey guys I hope someone can help pleeeease. I have a 68 camaro 396, 4 speed, 12 bolt rear end. It has normally been running around 180f. I recently changed the intake and carb. The only thing I messed with was changing the thermostat and the timing. The thermostat is a 180f NAPA part and the timing is at 33 total advanced around 2500-2800rpm, at idle it is 12 advanced from what my friend said he set it at .

Now my car runs almost to the "H" if I let sit and idle for 10 minutes, but runs around 160-180f when I start driving it, what the heck can it be? All suggestions welcomed.

I installed another 180f thermostat and changed the coolant again 70%coolant, 30% water with water wetter added. Also changed sending unit.

thanks guys I will recheck timing and recheck how distributor dropped in.

Also, the glycol antifreeze isn't an effective coolant. Only run as much as you need to protec the engine from freezing. Run as much water as you can. You may not have enough water in your system. I'd say that you probably have too much timing at idle as well.Beween these twoyou'll probably find your problem. Never use more than a 50/50 mix of anti freeze/water.

Is the fan shroud in good condition? Is the fan belt loose? How close is the fan to the radiator? If it's a clutch fan, is the clutch working? 70% glycol is too much. As was said, maximum glycol should be 50%.

At idle, the only air movement across the radiator is created by the fan blades, so a car that runs in normal operating temp while driving could easily overheat at idle if there is a problem with the fan or shroud.

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Probably a good idea before installing a t-stat, is to test it in a pot on your stove and see if the spring is working (opening/closing).

Regards,
Den
'67 Camaro RS

What do you guys think my timing should be set at idle, it currently stand at 12 advanced with no pinging.

Fan shroud and fan belt are fine, like I said it ran very well and cool until I changed carb and intake.

I checked thermostat in water and it works fine, the fan clutch is good.

Tomorrow morning I am installing the old set up and see what happens if it stays cool again then I do not know what the heck is going on. I may just stay with the old set up if it works, I was just trying to get my car back to stock by installing the L78 intake back on.

Set the timing at 15* initial with no vac advance hooked up if you have it. Big blocks usually like about 15* initial and 20* mechanical for 35* total to run their best.
before you make any changes it is always a good idea to check timing, vacuum etc... so that you have a benchmark for later.
As far as the distributor being 1 tooth off all that would do is require you to turn it farther to get the correct timing possibly hitting the firewall. Don't bother pulling the distributor.
Also check to make sure that you don't have any air in the system, sometimes it gets trapped causing cars to run hot.

Couple minor things come to mind. First, any chance there is air in the system? I usually drill a 1/8" hole in my thermostat flange to help burp the air out when refilling. Second, those OEM cooling systems need about 1-1/2" of air in the top of the radiator or else they'll burp out the excess. Some folks have retrofitted a puke bottle to their cars for this. In either case, is it possible that the car isn't actually overheating but rather puking out a little coolant due to one of these two issues?

thanks guys for all your help it is greatly appreciated

........... I usually drill a 1/8" hole in my thermostat flange to help burp the air out when refilling.............

That's a great little tip. I'm gona start doing that.

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Classic symptoms of either inadequate airflow at idle or not enough idle timing. Is your vacuum advance connected to manifold vacuum or to "ported" vacuum, and is it working? You should have around 27* advance at idle for good idle cooling (12* initial plus 15* from the vacuum advance). The vacuum advance can should be spec'd so it's fully-deployed at least 2" Hg. below whatever you're showing for idle manifold vacuum.

:beers:

Well here's my experience and some help hopefully.

JohnZ as usual...has beat me to the punch! Full manifold vacuum advance is the ticket at idle. Usually at least 22* or more is a good thing and sometimes depending on your VA it can be as much as 40 without a problem. I would stay under 30* however. If timing is not the issue then read on.

The fact that the radiator cools at cruising speed is a good sign..and usually indicates an airflow issue at idle. But, more can be at work.

So, first......do you have a clutched fan? If so, how old? This may be a tell-tale sign of things to come with a clutched fan going away.

By sitting for 10 minutes or so and gradually rising... I am sure it's not air. But, you can drill a hole as one has suggested to make sure however this compromises the thermostats temperature point management and will sometimes (depending on hole size and how many) will cause the engine to never reach full operational temps...which should be at least 175...and makes for a poor heater usually too. 160 is simply too cold for any efficient and power making range.

As others have also pointed out, 70% of antifreeze is too much. Actually you have more protection with 60% solution..which is the absolute. But, 50% is recognised as the "default standard" for solution mix and as others have suggested... the more antifreeze and less water, the less BTUs get carried away due to the specific heat number diminishing with the solution.

http://www.gi.alaska.edu/ScienceForum/ASF6/images/680.jpg

Lastly, quite frankly...the "H" part of the gauge is an unknown quantity! I would shoot the intake thermostat housing with a good IR gun to see what it's really reading at that indication for a base calibration. YOu might be surprized. And... running at least a 12psi cap and as long as you are NOT losing coolant, I wouldn't worry too much.

Keep everyone posted on your trials and tribulations. Good luck.

I wonder if your just loading up at idle look down the carb when hot , check if fuel is coming out main jet, Even just a liitle drop from their would cause it to get hot at idle.. or for that mater how rich is it set?

Found problem guys, the temp sending unit was for a idiot light not gauge. Boy do I feel like the idiot.

thanks to everyone for there input and help

JERRY