cdrag264

I know this has been asked numerous times, but I just can't find the answer. I'm hoping someone will have a fix. I have a '64 327 it was originally a 300 hp engine. It is putting out about 350 hp due to replacing the stock cam with a Comp Cam (CL12-212-2), a new Holley 1850-10 600 CFM (Model 4160) and I went to a stock 365 hp alumimum intake manifold (3844461). It runs great, BUT, I keep having a problem with the water temp max. out. The car has been completly rewired, new temp sending unit, new gauge, new alumimum radiator. Everything under the hood has be replaced. It was running great, temp wise, until last week. While driving its fine, but when I get into any type of traffic, or stop and go driving the temp gradually increases and will go to 240 deg. I've had 3 temp sending units in, new thermostats. Could the fan clutch be a cause? Any input would be greatly appreicated.

MikeM

Assuming you have verified the temp guage is reading correctly........

Are you sure the block doesn't have an air bubble in it? Crack the fasteners loose at the thermostat housing. That will let any air escape.

There's probably more archived posts on overheating than any other subject.

62Jeff

Is your car overheating, or is the temperature gauge simply telling you that it is?

Donald #31176

Ascertain first the actual engine temperature with an IR thermometer taken from under the upper hose. Check the air flow thru the radiator by putting a towel in front of the radiator. Check to see whether the correct vacuum advance canister is on the distributor. I suspect with a high overlap cam you have low vacuum and need a more aggresive VAC.

cdrag264

Not sure about the air bubble, but I will check for that. At times it has pucked water out the overflow tube, but not always. I will also get an IR thermometer and check under the hose to see if gets the same readings.

MikeM

I'm sure you know the surge tank is supposed to be only half full, hot. Also, have the pressure cap checked to see if it holds pressure.

toddalin

Yes, by all means check the fan clutch. Also, make sure that all of the seals between the radiator and fan shroud are supple and sealed so that ALL air must pass directly through the radiator. These seals play an important role than many overlook.

Interesting that I had my '64 out yesterday and up on the freeway on the way out to California Speedway, the car was running right at 180 degrees in the morning. But later in the afternoon (when it hotter out), on the way home it was running at 160-165 where it usually runs (160 degree thermostat). I think either my thermostat was sticking and self-unstuck, or I burped a bubble.

MikeM

This would seem to eliminate a LOT of possibilities:


"It was running great, temp wise, until last week."

65 vette dude

I'm betting the fan clutch is a goner.

cdrag264

How do you check to see if your fan clutch is bad.

BarryK

bring motor up to operating temp than shut motor down. Fan blade should come to a complete stop within 1-3 revolutions. If it takes longer than that or simply free spins the fan clutch is bad and needs to be replaced.

JohnZ

What work was done on it last week?

foliva

I would check the following:

(1) The temp sender/gauge pair may not be accurate. The senders have a very large variation in their characteristic. This can be checked a couple of ways. The first would be to use an IR gun as previously mentioned. In this case, shoot the sender case with the gun, and see if the gauge is reading what the gun reads.

The other way to check the sender/gauge pair is to remove both from the car, and wire them both up to a 12-14 Volt DC supply on the bench. Immerse the sender bulb in a pot of water heated to 180 deg F.
The gauge should read the same value. I use 180 deg because that is the center reading of the gauge.

(2) Check the fan clutch(as mentioned). The fact that the car overheats in traffic is an indication that the clutch may be bad. Is the clutch an original unit, or is it new? On original clutch probably is bad -- very few originals are still good. Note that new replacement clutches are designed to engage at a higher temperature (around 200+ deg). If the clutch is bad, the 1-3 revolution rule of thumb mentioned is a good one. You'll find that if the clutch is bad, it'll freewheel FOREVER when the engine is shut down.

(3) Check your ignition timing - both initial AND running. I'd use a dial-back-to-zero light & make sure that you're getting an appropriate amount of timing advance throughout the entire RPM range. Since the car has been modified, it may be tough to determine what the correct advance curve should be. I'd do a comparision against your stock curve as a sanity check.

(4) Check your thermostat. It could be that the thermostat is not opening. This is unlikely based on your description of the problem, but, it's easy enough to check with a pot of hot water. Be sure to use a thermometer to determine at what temperature it opens at.

(5) Make sure your radiator/surge tank cap is sealing properly. You can use a pressure tester to do this.

(6) After all this stuff, you might want to pull the radiator & get it checked. By the way, remember that water has better thermal transfer properties than coolant. If you don't use the pre-mixed coolant, be careful that you get the mix right.

Hope this helps.

cdrag264

Thanks for all the advise. I've been working nights and just didn't have the time to do everything. tomorrow I'll start and check all you have mentioned.
foliva-the clutch is not a new one. That is probably the only thing I didn't change when I restored the engine/engine compartment. Stupid me. I'm going to check the clutch tonight. Again thanks for all the help. You guys on this forum are have a vast amount of experience and knowledge. Us novice guys really appreciate that.