if the psi does drop and you have no external leaks then you have either bad gasket or head! If you end up pullin the head off and find a bad gasket, might as well take the head in and have checked cuz you don't know if the owner before had this problem and kept driving it this way! If they did it might have cracked the head! Usually inline 6's can handle the heat cuz there is so much material there!

 

Ok im updating this thread because I still am having an issue. I thought I had solved it and my overheating is greatly improved but I am still having an issue at highway speeds.

I pulled the head, there were no cracks that i could locate. I cleared the water jackets of any obstruction. Replaced the head gasket.

Things ive already done.

New original dimensions radiator
New 180 thermostat
Installed Refurb water pump
New upper and lower Rad hoses
Cleared water jackets
Replaced head gasket
Made some spacers to get the rad closer to the fan

Things im going to do

Check timing
Replace 13lb cap with 18lb cap
Anti-collapse spring for the lower hose

Things im considering doing when I can afford to $$

New 4 core aluminum rad
Electric fan


Like I said I thought I had it solved and my overheating is now much less severe than it was but its still there. Now I have to run it at about 20 mins hwy speeds to get it to overheat and I can get it the temp to come back down if I slow down or stop and idle. Soon im going to have to travel about 100 miles to my new home through hot houston weather and I need to get my truck to stay reliably cooled.

Please if anyone has any other thoughts as to what it could be please suggest away.

I appreciate any advice.

 

Do you have coolant loss puddling or have to add coolant frequently and are you using a 50/50 mix? Do you also have a recovery system?

So you know, the recovery system was one of the very first mods I made to my '66. I learned during my first go around on the '66 Mustang after repeated overheats to add a system. Once I added the system, the car stopped over heating completely. You can loose a tremendous amount of coolant at Hwy speeds and when the system stabilizes....if there is no recovery system.....all you're doing is sucking air. At least this was my experience. My memory is telling me this is a correct assumption so.........Hope it helps

 

I have basically the same setup as you, and I have quite the reverse issue. I put a slightly larger radiator I bought at Advanced Auto, and my truck barely gets to temp. I drive most of the day without any concern of of heating up much less overheating. Do you know that water is moving through the engine??

 

the coolant is just above the cores in the radiator right? or are you actually losing coolant?
also when you say that you could not locate any cracks did you just look for a crack or to you have it magnafluxed?

 

@ oldschool, No I dont have any coolant loss. Everytime I check my fluid its at the same level in the rad. What exactly are the benefits of a recovery system? I have a mix of 1/3 antifreeze to 2/3 distilled with water wetter.

@broomfield, Yes water is moving through the rad and it pumps water out of the top when im flushing it.

@fchase, No coolant loss, My fluid level is a little above the cores in the rad and stays there. I did not magnaflux the head, I visually inspected it as thoroughly as I could

 

Double post....... I apologize

 

A 50/50 mix is highly recommended especially if you are over heating. Water boils at 212F but when you add the coolant it's boiling point is substantially higher. In all my years I have leaned that you should not run anything else. Basically more water can cause the issue you are having and more colant is just a waste of money.
The recovery system captures the coolant and allows it to be automatically brought back into the radiator as it's needed. In a pressurized system, you should not have a huge airgap....just above the coils as you mentioned......and the radiator should be full at all times. If you're running the coolant water ratio you are, the added air space allows for things to reach the boiling point and then you overheat. I'm going back more than 30 years for unused memory so if I made a mistake in explaining things, please excuse me but.....I think I've got most of it down still. My 300-6 runs a constant 190 with a recovery system.

This is not saying you NEED a recovery system but every vehicle I've ever owned has had one installed either by the factory or me. Regardless of the technical reasons, it does save cash in the long run too.

Have you tried a pressure test to see if you are loosing pressure in the system. That could be an issue too. Pin-holes in the core, the thermostat not seated properly ,even a loose hose clamp can all contribute to things. Not trying to imply anything or say you missed this but have you checked the thermostat to see if it's in backwards? The copper cylinder or button faces the cylinder head.

Have you wire brushed the thermostat housing and cleaned the surface completely for the seat between the hose and it and itr and the engine? That's another culprit.

I'm out of ideas now....other than a cracked head, bad freeze plug or cracked block (but you would have coolant in the oil on that one) so.....unless I can think of something else....that's all I have.
Good luck with things.

 

should have magnafluxed the head! my shop does it usually for $40-$50!

 

Since you're still at a loss in your fix I'll throw this out just for the heck of it-are you sure the water pump or head gaskets are not partially blocking any ports?You might check to see if the fins on the rad are not all bent and not letting ENOUGH air to pass through.And at the risk of sounding stupid I've actually taken things apart to fix 'em and finding nothing wrong put it together and it mysteriously works fine.But thats just me.Of course I also always make the wrong turn first at a "t" in the road no matter what I do!

 

change the water pump first wondering how much distance between fan and the radiator

 

You mentioned that you have a flex fan. Those aren't necessary on these sixes. The standard issue steel fan is fine. The flex fan might even be contributing to the issue.

That also leads me to wonder about a question asked above....do you have the spacer in place between your water pump pulley and the fan? If the fan isn't positioned correctly, distance-wise, from the radiator, it will contribute to overheating.

When you had the water pump off, did you take some time and spray/flush out the water passages that are front-and-center there in the hole that water pump sits in? Cylinder number one is literally sitting right there and you can look and feel around in there and get a rough idea of how clean things are, at least at that end of the water passages.

Both of my slicks have been sixes. My first one was a 300 and the current one is a 240....and with both of them, my issue has been with them running too cool. If you have overheating issues with your 240, it'll probably end up being something of consequence and not something nitpicky like the water-to-coolant ratio not being perfect.