65' l-76 overheating - city driving

[David K.]

[Joe L.]

Re: 65' l-76 overheating - city driving

I'm getting tired of the situation……..Changed coolant with Zerex G-05 in 2015 (500 miles ago), and changed out the thermostat with a Robert Shaw 180o unit same time.
After running car for about 5-6 miles (I admit it's short distance back street driving between stop signs)….the temperature gets up to about 200-205 degrees. Settles down to 190 when I run on open road for about a mile. IDLING AT A RED LIGHT WORSENS THE SITUATION.
Exterior temp is about 85F. The car ran last year at 180f steady……….. What are possible causes ? I have an extra (new) thermostat on hand, and have already topped of the expansion tank with coolant.

Thanks in advance.

Dave------


Are you sure the reading is accurate? Have you checked it with an IR gun? Have you run a block test to see if combustion gasses are getting into the coolant?

In any event, based upon what you described and assuming the temp reading is accurate, I'd suspect a deficient fan clutch.

[Gene M.]

Re: 65' l-76 overheating - city driving

I'm getting tired of the situation……..Changed coolant with Zerex G-05 in 2015 (500 miles ago), and changed out the thermostat with a Robert Shaw 180o unit same time.
After running car for about 5-6 miles (I admit it's short distance back street driving between stop signs)….the temperature gets up to about 200-205 degrees. Settles down to 190 when I run on open road for about a mile. IDLING AT A RED LIGHT WORSENS THE SITUATION.
Exterior temp is about 85F. The car ran last year at 180f steady……….. What are possible causes ? I have an extra (new) thermostat on hand, and have already topped of the expansion tank with coolant.

Thanks in advance.

David you need to provide more information. Original radiator, water pump engine rebuild, overbored size, assume no air condition added, fan blade and clutch, are radiator and shroud all intact, with fan in proper position. Did this just start problem, was timing changed? You see the background may help the guys diagnosis your issue better.

[Harry S.]

Re: 65' l-76 overheating - city driving

David, did it start after the coolant change and the thermostat? If yes, sounds as if you have air stuck in the system.

[Timothy B.]

Re: 65' l-76 overheating - city driving

Why did you need to top off the overflow tank? What pressure rating of radiator cap and are you sure it's holding pressure and not letting fluid out while driving causing low fluid in the system.

[Duke W.]

Re: 65' l-76 overheating - city driving

A common cause of low speed traffic overheating is an inoperative VAC. The OE 236 16 should start to pull at 4" and be fully deployed at 8". Check it with a vacuum pump, and be sure that the signal hose shows manifold vacuum, about 10", at idle. Also check total WOT spark advance. With the VAC disconnected, verify that the centrifugal is all in at the OE 2350 spec, Then rev a few hundred higher and set it at 36-40 with a dial back timing light, as high as it will tolerate in that range with no detonation. If a new VAC is needed the Airtex 4V1053, stamped B28 is the correct OE replacement. Also as Joe says, check the fan clutch. It should have much more resistance to hand turning immediately after shutdown with the temp gage at 200 or more than when cold, and when hot it should take the about the same force to turn it through a complete revolution. If the amount of force varies, the silicone fluid is low.