68 302 Cooling issues

faastfixx · 02-19-2013, 11:31 PM

Hello all,

I am having a bear of a time tracing down a cooling issue on my '66 Coupe with a 68 302 powerplant. I have put about 900 miles on the car since I purchased it second hand. Ran like a top, then started slowly overheating, but only under a load. Engine has the standard .30 rebuild and a mild cam, nothing crazy. Stock heads, some underdrive pulleys (which I read could be a problem) I have done the obvious:

New thermostat (Yes it's in correctly and working at an idle in the driveway)
Inspected Gano inline filter and replaced it (It was clogged with what looked like bits of liquid gasket and small pieces of metal. From what I have read, a product of electrolysis from the silica in the coolant and the aluminum radiator.
Removed the Northern Aluminum radiator and had it flow tested at a radiator shop. They say its flowing perfectly.
I tried to belch the system with the radiator cap off and didn't get anything.

Water pump is not leaking, but looks to be flowing when I have the radiator cap off from what I can tell.

Talked to a local Mustang shop and they are at a loss as well.

Please, anyone out there have the same issues? HELP!! I searched the forum with no relative results.

Many thanks!
Jeff

Dylans '66 · 02-19-2013, 11:38 PM

If there is any air in the coolant lines, that can cause overheating. Have you tried running the engine with the radiator cap off to see if any air bubbles come loose?

-Dylan

faastfixx · 02-19-2013, 11:46 PM

Yeah, sure did. Ran it with the cap off for about 10 minutes or so. Never saw any bubbles, nor did the coolant level drop at all. It only overheats when Its under a load which makes me think there may be some sort of blockage in the block somewhere. Coolant was clean, no scale and radiator was clear. Likelihood of the blockage in the engine? I was told to try to run a garden hose through the bottom hose before I put the radiator back on.. frustrating

1969sag · 02-20-2013, 12:05 AM

I have a 69 with a built 302 and a 66 ranchero with new built 289. I have had similar problems. Mine with slow, hot cruises.
I suggest first jacking up the front of the car about a foot or two and then burping it with the heater on. It will surprise you how much more air will come out.
I recently used water wetter for the first time last summer. It did work great.
As always you should use a fan shroud, and you might want to upgrade your fan blade if haven't already.
Also carb could be running way too lean.

turbo2256b · 02-20-2013, 12:25 AM

Whats your timing set at?

wheelsup351 · 02-20-2013, 01:08 AM

food for thought.

how close is the fan to the radiator?

the timing could be too far advanced under load.

do you have a spring in the lower radiator hose? if not, it could be collapsing under load.

what t-stat are you running? 180 or 195?

how old is your heater core? any leaks there?

you could also be spinning the water pump too fast with an u/d pully.

Black65 · 02-20-2013, 07:40 AM

Define :slowly overheating.

What temp?
What kind of load?
How long does it take to "overheat"?
Does it cool down afterwards at idle?

turbo2256b · 02-20-2013, 08:55 AM

Not enough advance will overheat too. Have to figure out the ballance there.

One place AIR is always trapped is the water pump impeller cavity. Only vacuum filling or adding a bleeder in the pump will fill it completely.

69mach351W · 02-20-2013, 10:01 AM

Is the head gaskets installed properly??,,,,That would be a huge problem of overheating.

GT289 · 02-20-2013, 01:25 PM

I'm guessing the head gaskets were on correctly when he took custody
of the car. (drove it 900 miles apparently)
However, the head gaskets could be going "south." Maybe time for a
check for combustion gasses in the coolant. (block tester)
Another thought is the water pump impeller spinning on the shaft and
not connected solidly.
Head porting job where the exhaust port is now leaking into the water
jacket?

Chessgeezer · 02-20-2013, 02:46 PM

Is it possible that your temp guage is not working properly? You may want to pick up one of those infrared temperature guns and use that to check the engine temp.

turbo2256b · 02-20-2013, 04:01 PM

Some maybe most head gaskets have a tab somewith V notches that stick out the between front of the head /block when installed properly.

Pauly_J · 02-20-2013, 08:15 PM

Have you checked to see if your hoses are being pinched when the engine revs? may sound like a rookie mistake but alot of times the springs that keep them stiff go bad, happened to me, twice!

faastfixx · 02-21-2013, 12:27 AM

Thanks for all of the replies, some great things to consider here.

A few things I will add...

When I say "Overheating" I am referring to running it down the road and back after the car is good and warmed up. Bouncing off of the thermostat at 180 degrees when sitting in the driveway down to 160-180 degrees. As soon as I run it about a mile down the road up to 60 MPH or so and back. Sitting at the stoplight and running through my neighborhood, the temp climbs up to the 200 degree mark on the gauge.

I inspected the lower radiator hoses in response to Wheelsup351 suggestion about a spring in the lower hose, I dont see one visible, but I didn't notice that the hose is more pliable when I squeeze it one way verses the other. As if the hose may have worked a crease in the rubber. Really wishing I would have paid attention to that hose when I was revving the car! I guess I should just replace the hose since I'm there and they're cheap.

Another note is, when I drained the remainder of the coolant out of the radiator, it was an orange or rust color, could this be the pinkish residue from the "water wetter"?

I noticed some metal looking particles in the hose as well. Normal?

Thanks again for all of your responses, best forum for info I have ever been on by far! A true wealth of knowledge...

Best,
Jeff

faastfixx · 02-21-2013, 12:32 AM

Also, not too sure what the timing is set at, kinda curious why the previous owner ran "Water Wetter" in the car in the first place? Maybe there were some issues in cooling he tried to address.. Car seems to run perfect, no issues starting or anything leading me to believe timing is an issue.

Also would like to add that I am running a 180 Deg thermostat.

I have no heater box/core as it is blocked off at the waterpump. I am hoping there is air in the system and I can belch it as 1969sag mentioned, by jacking the car up in the front. Any other tips to burping the system without a heater system in place?