Robinhood 1977 dodge 440 heats up on freeway

Can you hear the fan clutch cut in?

Fan clutches run intermittently based on the sensing element for the clutch on the front of the fan axis. You can normally hear the "roar" when it cuts in, the temperature will then drop very rapidly and the clutch element will put the fan back to idle. The fan then spins over in idle until the whole process is repeated, if and when the temperature climbs back up.

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Does it have a thermostat in it? The engine will pass coolant so fast threw the engine that it will not cool with a bad or missing thermostat at speed.

Typically, the fan is not involved at highway speeds unless the configuration has a lot of restriction to air flow. Highway speeds are generally able to move more air through the radiator and engine compartment due to movement than the fan is able to impart.

A common issue is "chalked up" radiator (internal) tubes which are too restrictive to flow volume and in which the deposits ("chalk")insulates the coolant from the tube and so reduces heat transfer. The radiator may appear to be clear but having it checked by or pull and take to a radiator shop. They should be able to flow test the core for volume.

+1 on ronfisherman's reference to the lack of a thermostat. No way to know what you mean by "I have been through the cooling system" but please do not take offense by the suggestion that you may not have the expertise to identify issues. We used to see this frequently when was still in the business as the causes are not always evident to the inexperienced. The problem created by not having a thermostat installed is not excessive coolant flow rate but rather turbulance and changed flow path.

A bad thermostat is a common cause of the symptoms referenced because a thermostat which has a partially depleted wax pellet will be unable to open completely. Any time and engine is overheated, IME, the thermostat should be replaced.

Another possible is that the lower radiator hose is collapsing and so restricting flow. These hoses usually have a coil spring inside the hose or a reinforced wall structure to resist collapsing under "suction".

The Chrysler V8's of that era were bad for filling the cooling jackets with sludge/mud and often would benefit from flush using a back-flush machine using air bubbles.

If you have not compared radiator inlet & out;et tank temperatures under load, you may be advised to do so as this will indicate heat transfer efficiency.

Another possible is that there is so much heat introduced into the cooling system from the automatic transmission that this is driving the cooling system over its ability to extract heat. A large transmission cooler can be the solution to this issue, but again, measurements by an experienced professional may save you money in the long run.

Of course there is the possibility that the engine is not actually over heating....? What are the indications of excessive temperature? If the dash gauge, have you checked to ensure that the temperatures are actually high?

Hope something here is helpful.

NormK wrote:
Another possible is that the lower radiator hose is collapsing and so restricting flow. These hoses usually have a coil spring inside the hose or a reinforced wall structure to resist collapsing under "suction".

First thing I thought of. That's where my money is.

I'm with NormK on this one. Cooling system gradually loosing ground with the normal heat generated by the engine. Partially restricted radiator probably.

. . .Gradual heating up at Freeway speeds would indicate that the radiator is plugged up - suggest looking in YP for a Radiator Repair Shop!!! Also, the MoPar 440 engine REQUIRES a BALANCED SLEEVE Thermostat & WILL Run Hot if you install a REVERSE POPPET Thermostat!!! Robertshaw is the ONLY Mfg. of the Balanced Sleeve Thermostat. . . If your air cleaner is intact you will see a decal on the air cleaner stating this!!!!!!!!!!!!!

I'm thinking restriction too. Does "been through the cooling system" mean the radiator was replaced? If not, just replace it. They are pretty cheap.

If the unit has a viscous fan clutch, and the clutch has gone south the fan will block air from passing through the radiator.

At freeway speeds the fans with fan clutches actually turn backwards in the air stream, and you will see the temp go up if the fan is actually turning with the speed of the engine, the fan is runing to slow for the air coming into the radiator area, and actually creating a wall or air in front of the radiator.

navegator

That is really the classic symptom of a clogged radiator. It certainly would not be a waste of money to have it boiled out by a radiator shop and I'm sure it could use it by now.

I agree with ScottG.

What I learned was many radiators after 10+ years start becoming less effective. It can be due to cooling fin separation from the tubes/crud inside or a combo of the two.