Odd engine heating prob.
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Senior User
Joined: Apr 2004
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From: Spokane, WA
Odd engine heating prob.
I have a '78 F250 cc, w/400 and 4:10 gears. The truck never gets hot in the city but will heat when driving on the freeway about 60 MPH. The shroud is in place and the fan is a 5 blade 17" flex fan. The shroud has a 21" hole. Do you guys think it would help to use a 19" 7 blade fan with a clutch? I have never had a rig that heats on the freeway, they usually heat when sitting in traffic. If I pull over and idle the temp drops slowly, and driving around on dirt roads at 35-45 mph it doesn't heat at all.
Thanks in advance.
Thanks in advance.
Postmaster
Joined: Jul 2005
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- Check the water pump for wear.
- Verify that the fan blade is installed correctly.
- Check radiator hoses for deteriation externally and internally.
- Check radiator for build up of contaminints or corrosion.
- Verify the water pump belt is tighten properly.
How dirty is the radiator fluid?
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Senior User
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From: Spokane, WA
The fan is 80% in the shroud but I do not like the 1.75" space between it and the shroud. Fan is installed the correct direction. New rad hoses. New coolant. Water pump belt is good. I have not checked the water pump, but I have a new Edelbrock sitting in the garage I got a super deal on. Do you think the larger 7 blade fan will improve things? This would shrink the space between the shroud and the fan to 1". It seems odd that it only heats on the freeway. Perhaps the flexfan is actually impeding airflow at high rpm?
Elder User
Joined: Jun 2003
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From: Houston/Hope BC
This is a lack of heat exchange capacity problem. You are only having trouble when the engine is producing beyond a certain level of HP (heat) independent of airflow. 30 MPH will provide as much or more airflow than any fan. Prime (but not only) candidates would be corroded/impaired radiator, T-stat not fully opening, poor pump.
Open the cap and observe flow as the engine warms up. Put a few K RPM to it and you should see a virtual torrent of flow. (Be careful of your eyes.) How does the radiator look through the cap? Is there a bunch of mineralization around the tube openings? Fins staight and clean? Run it without a T-stat temporarily and see if the problem goes away, this is fast and almost free, and gives you a chance to boil the T-stat and see it works. GL
Open the cap and observe flow as the engine warms up. Put a few K RPM to it and you should see a virtual torrent of flow. (Be careful of your eyes.) How does the radiator look through the cap? Is there a bunch of mineralization around the tube openings? Fins staight and clean? Run it without a T-stat temporarily and see if the problem goes away, this is fast and almost free, and gives you a chance to boil the T-stat and see it works. GL
Elder User
Joined: Dec 2004
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From: Springfield, OR
Check to see that the spring is present in the lower radiator hose. At higher rpm's the hose can suck in on itself and restrict coolant flow and give you overheating. Your symptoms are classic signs of that.
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I have a 300 6cyl that is doing the same thing. Great in the city, but when im cruising at 60 - 65, she heats up to the hot level. Never boiled over though. I was gonna replace the rad and heater core as my rad looks shot. Also I may of plugged it all up using BARS LEAKS to fix a heater core problem. Circulation may be restricted if you used that in your rad. thats what im suspecting happened to mine. Other than that she runs good. Its a 79 f250 .
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Joined: Dec 2001
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From: Louisville,Ky.
Yes the radiator is suspect. The coolant is moving much faster at highway speeds, especially with 4.10 gears, so if it is partially clogged, what coolant that is circulating, isn't staying in the radiator long enough to properly cool off. Stop leak will definately clog a radiator.
Since these radiators are down flow, as sediment settles to the bottom, all flow is restricted. Make sure that there is a thermostat in the engine, because without it, coolant flows too quickly to cool as well. Like mentioned above too, make sure that the lower radiator hose isn't sucking closed and restricting flow.
Since it is staying cool at low speeds, this would rule out the fan or shroud.
Since these radiators are down flow, as sediment settles to the bottom, all flow is restricted. Make sure that there is a thermostat in the engine, because without it, coolant flows too quickly to cool as well. Like mentioned above too, make sure that the lower radiator hose isn't sucking closed and restricting flow.
Since it is staying cool at low speeds, this would rule out the fan or shroud.
Postmaster
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Oops,
This computer is quick, here the thread. https://www.ford-trucks.com/forums/s...ght=vapor+lock
This computer is quick, here the thread. https://www.ford-trucks.com/forums/s...ght=vapor+lock
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Senior User
Joined: Apr 2004
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From: Spokane, WA
Thanks guys, will do some checking and as soon as I have an opportunity. I have never used stop leak, but who knows about the past owners. I did put the spring back in when I changed the lower hose. I will have to get my other car fixed before I can put the truck out of service for a while. I suspect the rad. as well.
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Senior User
Joined: Apr 2004
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From: Spokane, WA
Hello again,
I got looking at my truck today aqnd checked the timing. With the vac line off the dist. it was set at 12*BTDC. Then I plugged the vac. line in and it went to over 30*BTDC. If I am not mistaken shouldn't the dist. only get vacuum when the throttle is open? I am running a Edelbrock 1406 and the dist was plugged into the driverside vac. port full time vacuum. I moved it over to the passenger side and now I can see the timing advance only when you rev the engine. The idle also dropped about 100 rpm when in neutral when I moved the line. I have now hooked the Egr to the fulltime vac. port (drivers side) think this is a problem? The line runs from the carb directly to the EGR. I noticed that my book shows a rather elaborate control system for the EGR, that is completely missing on my truck. I am also worried about what jets the previous owner may have installed in the carb. I still need to pull a plug and check the color. Anything else I should check? Am I on the right track?
I got looking at my truck today aqnd checked the timing. With the vac line off the dist. it was set at 12*BTDC. Then I plugged the vac. line in and it went to over 30*BTDC. If I am not mistaken shouldn't the dist. only get vacuum when the throttle is open? I am running a Edelbrock 1406 and the dist was plugged into the driverside vac. port full time vacuum. I moved it over to the passenger side and now I can see the timing advance only when you rev the engine. The idle also dropped about 100 rpm when in neutral when I moved the line. I have now hooked the Egr to the fulltime vac. port (drivers side) think this is a problem? The line runs from the carb directly to the EGR. I noticed that my book shows a rather elaborate control system for the EGR, that is completely missing on my truck. I am also worried about what jets the previous owner may have installed in the carb. I still need to pull a plug and check the color. Anything else I should check? Am I on the right track?
Postmaster
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From: okc
i had this same problem with my 460, i replaced everything in the cooling system trying to figure out the problem with no luck....since your overheating on the highway (like mine was) the fan and shroud are ruled out because you get more airflow from highway speeds than any fan can give...i fought the problem for 3 years and went crazy in the process....turned out my block was clogged....i recently tore my engine down and put new gaskets on everything, when i took the heads off i noticed the back half of my engine's water jackets had muddy brown water while the front half had clean green antifreeze....the radiator sealer i used clogged the water jackets and only half my engine was being cooled....on city streets it never got hot, but on the highway at 60+ mph it would climb all the way to 280 degrees!!! then drop to normal as soon as i slowed below 55!!! i hope this isnt your problem because you have to tear the engine down to fix it...FYI: i flushed my engine 10 times or more so i thought it was clean...till i pulled it apart and got that nasty surprise!! good luck with it........