Ive got a problem with my '69 with a 351w over heating when driving 70mph for 20 or more miles . If I slow down below 65 it’s fine,and can also drive around town in the heat with no problems. Any thoughts?
Do you have a thermostast in place?
Might check and see if the internal spring is still in place on your lower radiator hose. A quick squeeze to the hose will tell, it should feel stiff,…unable to compress by hand. The spring is in there to prevent to collapse of the hose under high rpm and heat.
Yes it has a thermosat in place,put it in four months ago. I will check the hose when I get off work tomorrow.
Thanks for responding.
what’s the rpm at 70mph?
Cooling requires two things: circulation of enough coolant, and circulation of enough air. At 70 you are getting plenty of air. That means that you are not getting enough coolant circulation. Most likely this means that the radiator is partially plugged up.
I agree that a plugged radiator is the most likely cause. But too much coolant flow can actually cause overheating at high engine speed because the coolant does not spend enough time in the radiator to cool down. No Tstat, wrong Tstat or stuck open Tstat etc. Ford FE engines had too much coolant flow from the factory and need an under drive on the water pump if the engine was run at high rpm for an extended periods.
Bill
Bill, You have the right reason, but they wrong location. Let me explain.
Guys that work on lots of cars see cars that over heat because they have no thermostat installed. The common belief is that the water circulates too fast ans doesn’t have time to cool off in the radiator. The part that is true is that there is a circulation problem, but is is in the engine, not the radiator. The thermostat does act to restrict flow, the purpose is to insure that every coolant passage in the engine is always filled with coolant. If an area does not fill, then it gets hot and when coolant hits it, it flashes to steam. The hottest part of the engine is the top end: the heads. Water wants to seek its own level, and stay low in the block.
There are two other reasons why it is impossible for water to go through the radiator too fast for it to cool off. First, the rate of heat exchange is a function of the difference in temperature. Hot moves toward cold, and the bigger the difference, the faster it moves. If the radiator is almost as hot as the coolant, it could stay there all day and never cool off. If the radiator is cold, the greatest amount of heat transfer happens very quickly. This is the concept that you have to get your head around. It isn’t how long the coolant stays in the radiator, it is the temperature difference that counts. If you drop a burning coal into hot water, it cools off almost instantly. Hot water in a cool radiator does the same thing. The closer in temperature the coolant and the radiator become, the slower the transfer rate. So if you don’t have enough air carrying the heat away, and the radiator gets hot. The car will over heat.
Then there is the hardest part to get your head around. In a closed system, the faster the coolant flows it still spends the same percentage of the time in the radiator. This is why guys buy high volume water pumps. They want the water to make two trips through the radiator in the same amount of time as a regular pump. Think of it this way. If it takes 30 seconds for your stock pump to circulate 4 gallons of coolant through the system, the coolant will spend about 25% of that time in the radiator. If the high volume pump can move the coolant twice as fast, then the coolant will pass through the radiator twice, in 30 seconds, but it is still spending 25% of the time in the radiator. And the biggest cooling bank for the buck happens the instant that the hot coolant hits the relatively cold radiator.
These are not my opinions, just physics.
It feels like part of the spring is missing / rotted away. I guess i’ll have to get a new one.
I don’t know what rpm it running at 70, but at 60 its turning 2500rpm.
Also it does have the small radiator and no a/c.
thank you Bill. I am so sick of all the B/S about coolant not staying in the radiator long enough to cool down if you remove the thermostat.
The function of a thermostat is to keep coolant in the block so it heats up to the most efficient operating temperature. The water still circulates at the rate goverened by the capacity of the cooling system and the speed and efficiency of the water pump. air flow over the surface area of the radiator that has coolant in it (when it is blocked the coolant cant circulate and capacity is reduced) maintains the coolant temperature, in conjunction with the thermostat. A fan and a shroud maintains airflow efficiency
Ford Australia used to run fixed blade fans (no clutch) on most of its V8s and the hot weather kit included 24" three row radiator and 160 degree thermostat, until the emmission controls kicked in and they went back to 180 for emissions efficiency
These guys have designed and built radiators that do multiple passes through the core to assist with cooling
Going to agree with Mr. Bill B. on this one. No such thing as too fast of coolant flow. If you feel around the radiator after a short drive and feel spots that are cooler than others, then the radiator is likely plugged up in spots.
I also think I get what Andy is looking for. If the RPM’s are real high, then the water pump could be cavitating and loosing flow, but I don’t think this is the case at around 3000 RPM at 70. Cavitation doesn’t usually kick in until closer to 5000.
Newb question, then…in a “topped off” closed system, wouldn’t cavitation be unlikely, if not impossible?
Lets get to basics first: Systems under pressure will have a increased boiling point - adding ethy-glycol or other additives also increase boiling point (under correct perecentages), cavitation is indicative of poor design since the fins/rotors “beat” the fluid rather than push it. (rarely the problem). Things that are common problems are things like rad hoses collapsing under highewr RPM’s because they are to soft under heat or the run is to long - a spring/wire support helps relieve that. Other things - not holding pressure (#1 cause - bad cap/loose hose/bad hose/pin hole in rad/freeze plugs/head gaskets), wrong head gasket orientation (very easy to do on SBF), lack of flow restictors in clevo’s (“hat” under thermostat), plugged up rad, bad timing, warped heads, probably a few things not covered here. Pressure test is a good starting point if nothing is obvious - then drill down
Actually the boiling point goes up with the increase in pressure, and the spring is there to keep the hose from collapsing when the factory pulls a vacuum on the system to fill it during manufacturing.
Not trying to beat anybody up, just checking few myths…
From Kevin Marti…
I need a spring for my radiator hose. Where can I find one?
The thought that a spring is needed in a radiator hose is a common misconception, that springs (pun intended) from two events.
The first is that many (although not all) lower radiator hoses on the production assembly line had springs in them. The reason for this was the method by which the assembly lines filled the cooling systems. To save time, a special vacuum/fill fitting was placed over the radiator fill connection (the place where the radiator cap would eventually be placed. A vacuum machine was turned on to evacuate most of the air out of the cooling system. Once completed, the fill portion was turned on to introduce the coolant into the system. This process avoided entrained air preventing the system from being completed filled. The purpose of the hose spring was to prevent collapse during the vacuum portion of the fill cycle.
The second part of the story that has led to the “I need a spring” myth is that some people have observed their lower hose collapsing when they rev the engine. This is the result of a clogged radiator or a cooling system that has not been brought up to standard operating temperature. If an engine is revved up while still cool, there is only atmospheric pressure in the system. It is possible for the lower hose to collapse slightly due to the water pump drawing water out of the lower hose faster than the gravity-fed water from the radiator replaces it. Once the engine has been warmed up, the coolant system operates under pressure and this condition doesn’t exist in a properly maintained cooling system. However, if the radiator tubes have restrictions, as the engine is revved, the water pump pulls coolant from the lower hose faster than water can trickle past the clogged tubes. This can result in a reduction in internal pressure that would cause the hose to collapse.
Note that the events that lead to the thought that “I need a spring” are based on either an insufficiently warmed up engine or a clogged radiator. The spring does not take care of these events. It merely masks a symptom. If, after your vehicle has reached normal operating temperature but you experience a collapsing hose, have your radiator tested.
As an additional thought, have you ever wondered where your original spring went? Did you ever find bits and pieces of it scattered throughout the cooling system? Being made of ordinary steel, they corrode with time, small pieces gradually breaking off and either scoring the water pump impeller, tearing the water pump seal, or clogging the radiator. They aren’t necessary for the functioning of a properly maintained cooling system.
OOPS your right - got the boiling point backwards - LOL thinking one thing wrote another.
Ever seen a large ship, like a ferry, leave a wake of churned up white water, even though the props are submerged?
Mike guessed what I was asking.
Sure, but those are close enough to the surface, and not a closed system. Not doubting you by any means, just trying to understand the “how”…maybe our Physics professor can chime in…oooh, Adam??
Nevermind…just read up on it…gotcha. From Wiki…
Major places where cavitation occurs are in pumps, on propellers, or at restrictions in a flowing liquid.
As an impeller’s (in a pump) or propeller’s (as in the case of a ship or submarine) blades move through a fluid, low-pressure areas are formed as the fluid accelerates around and moves past the blades. The faster the blades move, the lower the pressure around it can become. As it reaches vapour pressure, the fluid vaporizes and forms small bubbles of gas. This is cavitation. When the bubbles collapse later, they typically cause very strong local shock waves in the fluid, which may be audible and may even damage the blades.
So, basically it’s akin to when you see a fighter doing high g’s, and the air(fluid) condenses into visible vapor…correct?
yeah, that’s a good analogy.
If you take a walk through the parts books, or google, you’ll notice that the higher performance engines like Boss 302 and 351 (the twitchy high revving engines), always used a different part number than the grocery getters.
Impeller design can minimize cavitation at rpm, or it can exacerbate it. So, all water pumps are not created equal.
Even the remarkably simple fix for diminishing cavitation on a mundane water pump just involves pop riveting a sheet of metal to the back of the impeller to prevent water cavitation around all of the impeller blade.
Just because the water molecules are together at rest at NOT doesn’t mean the H+ and O2 in there won’t separate under acceleration, vacuum presence, and heat. And then, of course, when you add ingredients like coolant, you get more chemical reactivity potential.
A lot of guys are building these high winding strokers nowadays from the W series (or torque beast 427’s) and the parts store water pumps (new parts, not reman ford stuff) that are being sold over the counter can have the cheapy cheap cheapest impellers made. They work ok in a work van plodding along at 2500rpm, but they cavitate when you put them in a performance engine and move the rev range out of the sweet spot.
So, all water pumps are not created equal because all impellers are not created equal. A sudden increase in heat can indicate cavitation due to loss of efficiency and volume of fluid pumped. Additionally, cavitation can cause hot spots and steam pockets in the heads, which can crack the head, chamber, etc. and cause a generally bad day.
So, if someone has an issue with cavitation, it’s something that needs to be addressed.
The change at 70mph was in the possible sweet spot for a car running a 3:89 or so gearset to be out of the intended efficiency range of a stock water pump. So, that’s why I axed.
Details like this are really subject to Ockham’s razor and I suspect the radiator is just clogged.
Thanks! I appreciate the education!
I was going to trade out my radiator with one I have from a '70 Moostang that had a 302 with factory air. But found out they aren’t the same,different lower hose location and mounts.Not as interchangable as I thought. Can a better/bigger core be put on the smaller radiator tanks or should I just buy a bigger radiator?