Cool/Heat: 57' GH Overheat problem

[Pdskinner]

What is the sequence to fix this problem. It runs at 200-210 degrees on a hot ambient summer day when less than 50 mph. It heats up to 240 degrees at speeds of 65mph on a hot day. It cools at idling and runs at 180-190 degrees at speeds less than 45 mph.
If the guage is reading correctly.
What order of probability should I check to diagnose the problem
Thanks

[GrumpyOne]

1. Plugged radiator

2. Stuck thermostat

3. Is that baffle in front of the radiator top intact? If not, air will allowed to pass through above the radiator instead of being diverted to it.

4. Dirty block

I'm sure that a few others will chime in with good suggestions..

[64studeavanti]

Check timing. If none of the above work, do a cylinder leak down test to determine if you have a blown head gasket.

[jclary]

1. Plugged radiator

That includes external as well as internal. Are the fins full of bugs? If you have a bug screen, is it clogged? I have even seen bug screens that were too fine, and restrict enough air, to cause overheating on a hot day.

[jackb]

plugged radiator...

[JoeHall]

Since it seems influenced by RPM, what is the rear end ratio? Is the heat riser valve wired open? Take the supercharger belt off, and see if that changes anything. (It only takes a couple of minutes to remove.)

Does it detonate or vapor lock at 240? If not, the gauge may be wrong. They usually begin to vapor lock around 225, and will then detonate under load, if you can keep it running.

Do a compression test. If much above 150, it may be that someone put higher compression pistons in it, which do not work well, in combo with the supercharger.

[Jeffry Cassel]

is it really that hot Take its temp I use an infrared thermometer which is very accurate but you can use a candy thermometer be careful cause if it is overheating removing the cap will send you to the emergency room Do not trust the original equipment temp gage they can be very undependable after all those years are you putting moonshine in the car? DONT! had a hawk with a GH engine in college it had a two row radiator and never ran hot not even at one hundred thirty eight miles per hour nowdays everything runs hot must be global warming and the skunk urine they pass off as gasolene

[Tom Bredehoft]

If the trash hasn't been cleaned from your block (recently) that's where I'd start. Take out the soft plugs and clean out the accumulated 'stuff.'

[345 DeSoto]

May not be appropriate to your problem, but I chased around an over heating problem in my Rolls Royce. I did everything imaginable to find out/fix it, but it steadily got worse. FINALLY tracked it to a bad viscous fan. Replaced it and my over heating problem is gone.

[thunderations]

Sounds like a circulation problem. Have the block power flushed, pull the drain valves out to get a larger exit for the "stuff" to come out. Have the radiator rodded and checked for flow. Install a new thermostat and you should be OK.

[jclary]

What order of probability should I check to diagnose the problem
Thanks

Well...Mr. Skinner...seems we kinda lost track of the above part of your inquiry. Aside from suggesting that you "first" make sure there is a belt driving your water pump, I believe you have some very good suggestions of what to do. However, you may have to arrange the "order of probability," yourself.

[karterfred88]

Well summer is with us. Your description indicates you do have a fan belt that's working, but you don't have sufficient heat extraction from the coolant. I can't tell you the proper order but all of the above ideas will help, but may not cure the problem. I'd start with the power reverse flush of the radiator and block, if it is allowed where you live and there is still a radiator shop with the equipment to do it. New thermostat, coolant and drive it to see if it works. Next up would be a rod out of the radiator-but be prepared to have to replace it, if it has been blocked up to the point of flow restriction, rodding may perforate the tubes and a new core needed. Although cleaning the block and internal head areas will help it, it has been running for many years that way and probably not just now start causing it to overheat. Good luck.

[Flat Ernie]

Generally speaking, if it overheats at speed, but is fine a lower speeds, it is your radiator - lack of flow. Conversely, if it is fine while moving, but overheats sitting still, it is generally an airflow problem. However, as has been pointed out, there are other contributing factors. I think you may have a multi-faceted problem generating your symptoms, but I'd begin with a good look at your radiator.

[JoeHall]

An easy check, that is often overlooked: make sure the lower radiator hose has coiled wire inside it, so it does not collapse at road speed RPMs, and restrict flow to the pump. Its east enough, with motor cool, just reach down and squeeze the hose, from end to end. It should not be collapsible, and you should feel the wire coils inside it.

[Pdskinner]

The temperature with the infrared thermometer was 160-170. My guage is inadequate. I will replace the sending unit and check for corrosion on the wires. Then if that does not work I purchased a guage on eBay.