my 65 valiant boils in higer speeds....i have tried everything(fixed the radiator,changed thermostat and water pump,and i have also checked the headgasket for leaks and flushed/cleaned the engine block)none of thees things helped,ingnition and carb is also tuned in god.but i read a topic here about radiator caps that it should be a 13lb cap on it........i noticed that my is a 7lb could this bee the problem??it runs hot only in higer speeds!!like after 50mph,i have had this problem 2 sumers now and im going mad sone

Have you checked to make sure your lower hose isn't collapsing at high speed? Is your heater core plugged? A 13lb cap will raise the boiling point off coolent, but make sure you don't have any other problems first.

sorry about my english skils,what is the heater core?some electric wire that gos to the heater??

The heater core is what the smaller hoses from the water pump goes to....a small radiator in the fire wall that supplies heat to the interior.

oh,yes the heater cores are conected....

most cars that are working with 7 pounds caps have shot radiator and/or possibly shot heater cores. But your overheating might be caused by the combination of several causes: collapsing lower rad hose, retarded timing, maybe your carburetion is lean at cruise and it's overheating, etc

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

An abnormal rise in temperature usually indicates a restriction or head gasket problem. Since you've checked the head gasket (did you use a leak down test or compression test?-a leak down is more accurate) I would check for a restriction. You could by-pass the heater core to eliminate that as a problem. You said your radiator was checked, are you sure it's flowing properly? Make sure the lower radiator hose is hot after the engine warms up (you'll know if the t-stat is operating ).
I would recommend eliminating all of your cooling components from problems first (that's normally the problem). If that doesn't solve your problem you'll have to start digging deeper.

By the way your English is fine, I've seen much worse from people who were born here. Good Luck, Dale

i have checked the head gasket bye taking of the head,the reason to this was to check if there was any dirt in the water chanels and to see if the gasket is ok.the gasket was ok but there was litle dirt in the block so i removed the dirt and bolted it back together and hoped it would be fine but to my disipointment i notised that nothing had changed i dont know yet if the lower hose is colapsing but i dont think it dos(i will check that sone too)and i am going to disconect the heater to but i dont belive the problem is there either(had the heater to the radiator shop too last vinter)but just too meantion i hav notised that every time i start my car after it have been staying some while......it sounds like there would bee some air traveling through the heater radiator??

i have now checked the lower hose colapsing thin and it dosn´t colaps,disconecting the heater didn´t help either.............what next

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Plymouth Valiant 1965
225/4bbl/904/7 1/4
HEI ignition/msd blaster 2 coil/mallory module

The low hose can fool you, after it get hot it get weaker & on the highway it even gets a vacume from the pulling of the water pump and it can suck it shut. If the hose doesnt have a spring in it put a spring inside it to totally cure this even being possible.


If this does not cure your problem then I would have to say it is the radiator. To over heat on highway does say it is a flow problem, now this can be caused by the radiator not flowing enough, or not enough air flowing through the radiator, or the water pump not flowing the water when the engine is at these speeds.

Most of the time it is the radiator, the only way to know for sure is to take it apart and check the tubes for flow because only part of them can be stoped up & just looking down in to test for flow will fool you on the results.

Now also the water pump belt can be a little tricky. It may seem the belt is tight but I have seen warn belts or pulleys or it just not being tight enough do this and not give any problem until you are at highway speed.


Do the spring in the hose first, then check the belt/pulley on the pump. If no cure is found here its time to go to the radiator.


There is one other uncomin thing that can happen and it would be the water pump propeller getting damaged enough that it doest move as much water as it should, I have even seen them rust away or be the wrong one to give proper pumping.

There is also the possibilty that one of the pulleys have be changed to the wrong ratio & it just does not spin the pump fast enough.



Jess

Agree!
Airflow isn't the problem here—inadequate airflow tends to cause low-speed/stuck-in-traffic overheating. At high road speeds, there's plenty of airflow through the radiator caused by the forward motion of the car. One cause of waterflow-related heating that hasn't been mentioned here is rust and gunk buildup in the engine block. If it gets to serious levels, you have to remove the core plugs and physically scrape/dig the crud out of the block, then flush it out with a high-pressure hose.
Probably not the problem. Not only would such a problem tend to show up at low engine speeds (not high speeds), but it's tough to find a different-diameter water pump pulley with the correct offset and bolt pattern to fit on a slant-6!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Just offering any possible idea that could cause the problem. And depending on things such as ( possible card board being put in front of the Rad and forgot about ) or mods in any way that could restrick air flow could & probably would cause high speed over heating from the higher levels heat being made. But it was one of the last things I meantioned as to be something out of the norm.



I think it was meantioned that the head was removed and water jackets cleaned in the block so maybe he is alright there, but still could be some that could not of been clean from this methode.

A diff pulley would be odd be people will do some strange things when in need and could of had one fitted from another brand engine, and resulting in slower flowing of the coolant.


But my guess would be that either, bottom hose, Rad or pump belt slipping is his problem. Maybe he will figure it out now with the different subjects that have been touched upon.


Jess

the radiator should flow good,the radiator shop dude didn´t only flush it whit some super cleaning stuff he alsoo take the "ends" compleatly of it and cleaned it bye hand(i wonder if i explained this in a way it can be understod?)anyway the rad is 100%clean and flowing.i will test the spring thing in the hose during this week(if i have the energy to do so,my motivation begins to bee low on this engine sone.....if i woant find the solution sone i pul it out from the enginebay and blow it up )and i already mentioned that i have a 7lb cap,and i read somewhere that it should be 13......which should add more presure?shouldent it keep up the presure in the hoses to which would prevent it from colapsin??(or is this only one of thous ideas i get when im too tired?? )and the way i checked the hose colapsing was whit a hot engine(alsoo the hose)i had it runing and i gave it some revs (3000-4100)for a while and the hose gave no since of colapsing...........

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Plymouth Valiant 1965
225/4bbl/904/7 1/4
HEI ignition/msd blaster 2 coil/mallory module