'74 Getting Hot

[Jon D.]

Re: '74 Getting Hot

Jon -

Could you expand on that or clarify it? In my 50 years of working on cooling systems, I expect to see the coolant temperature exiting the radiator at least 20* cooler than the temp at the radiator inlet, preferably 30* cooler for a properly-functioning system. Increased flow restriction in the core will result in a smaller temperature differential between the inlet and outlet.

John,
One would normally expect to see a higher drop in temp but more is not better in this case. At work we had a publication specifically for diagnosing cooling system problems and measuring the top and bottom tank temps was one of the diagnostic steps. I remember the 12 to 15 degree temp drop pretty well. If the core is plugged externally with things such as bugs, dust, dry grass clippings, or cottonwood seed fuzz the inlet and outlet tank temps will be very close to the same temp. If we did get a reading that we were suspicious of internal plugging, we would drain the coolant down and look inside the radiator through the filler neck or pull the top hose using mirrors and a flashlight for inspection. We never wanted to just start changing parts. Most service manuals that I remember did not have that information in them.

Another thing I remember is that it takes water to dissipate the heat rejection through the core. If the freeze protection is elevated it will not reject the heat from the coolant properly. Ideally one wants about -34 degrees which is about a 50/50 mix of coolant/good water. Use a refractometer to measure the freeze protection as the ball testers will not help for diagnostic work. A 60/40 mix can be used in specific cases but is not ideal for most applications. If the core is starting to have deposits build up internally this one can be an issue, not enough heat rejection.

The owner of our dealership owned many in many states. One of our emplyees that I knew well in another state purchased a 74 with a hot rod engine and transmission. He had heating problems from day one. He kept calling me for info because he knew I had a 74 and I was the service manager. He just kept changing parts without diagnostics and never did solve his problem. He finally sold the car.

Let us know what you find as thats the only way we gain knowledge.

Good luck

[Peter B.]

Re: '74 Getting Hot

I live in Miami (HOT TEMP). Same problem. Ended up being that the radiator was plugged up. A dip to get it cleared out ended up showing some pits that leaked so had the radiator re-cored. That means I used my side cans of the original and had the core replaced. Looks original and runs cool with the Hot florida sun and running it hard.

Good Luck

[Duke W.]

Re: '74 Getting Hot

I think that's the key, especially if the car runs hot at highway speed. Over time old fashioned "green" antifreeze builds up deposits in the tubes, which act as insulation preventing proper heat transfer performance.

The OP says the radiator "looks just fine" but unless he has X-ray vision he can't see the inside of the tubes. If a radiator has a cap on the end tank you can drain some coolant to expose the first few rows of tubes, and if you can see deposit buildup on the outside of the tubes that protrude beyond the end plates, it probably has similar buildup inside the tubes. External inspection of the radiator will only reveal leaks, which are evidenced by white stains.

If you have a brass radiator it can usually be "rodded out" to reduce the deposits or recored if there are any leaks in the tubes. Aluminum radiators cannot be rebuilt. A new DeWitts replacement is the only choice if you want to maintain originality.

Look for and remove the metal tag before you take the radiator to the shop. They will throw it away. When you get the radiator back, reinstall the tag.

Use of a modern HOAT antifreeze like Zerex G-05 will reduce the deposit buildup rate in the future.

Back in the mid-eighties at a Riverside event in July my Cosworth Vega was running 230F on the track at 105F ambient, so I had the radiator rodded out. Then about ten years ago it began weeping at the core end plates.

The shop said the core was fine. They ended up resoldering the end plates to the core then resoldered the tanks back on the core, and it's been like new ever since. I recall the job was only 75 bucks.

Duke

[Lenny K.]

Re: '74 Getting Hot

All good stuff....thanks a lot. I will drop the level in the rad and peer inside to see what I can see there....no sign of external leaks and I was running older prestone 50/50 mix so after I find out what is hoppening, I will consider updating my "technology" to newer HOAT. SHould get some time this weekend early morning (b4 the heat) to check a few things and I am about at the point of either getting recored or just replacing with a decent rad since my '74 doesn't flight anyway.....just a fun driver ....LK

[Duke W.]

Re: '74 Getting Hot

Once you drain out some coolant, so you can see at least the first half-dozen or so rows of tubes, if they have significant deposit blooms on the outside, pull the radiator and take it to a reputable radiator shop. They will pressure test it to 30 psi, then remove the end tanks so they can see the tubes. If they have interior deposits, they will "rod" them out, resolder the tanks back on, repressure test, and it should be good for another one to three decades if you use Zerex G-05 A "rod-out" is usually less expensive than a recore.

Don't just arbitrarily have it recored. If it does need recoring, get the tube and fin count and make sure the new core is the same or very close. This data should be in the AMA, specs and you can also manually count the fins/inch and tubes/in.

Don't forget to remove the metal radiator tag with the part number and production code so you can reinstall it. The radiator shop will want to install a tag for warranty purposes. Ask them to put it in an unobtrusive place.

You have an emission controlled engine that is intended to "run hot", and it will probably run hottest in low speed heavy traffic. You can reduce low speed heat transfer by converting the ported vacuum advance to full time and bypassing the TCS, if installed, but you may need a different VAC for this to be successful. Use an OE equivalent 195 degree thermostat.

If you want to go this route you need to report the ID number of the installed VAC.

Duke