74 cj5 Overheating intermittentently

I hope I'm not violating any rules here. I posted this question at the end of the '258 running hot 230-240' thread, but noticed that problem was solved so maybe the thread died. Here goes.

I've followed this thread (above) and will check the 'air in the system' thing tonight. I just flushed my cooling system Saturday, and ran it both Saturday and Sunday. On Saturday, it seemed to stay right at 180 or a little below. I'm in So Cal, cool outside. But Sunday, I was coming back from home depot and it started to creep up to about 200 or so..maybe a little above. It was still climbing when I got home and shut it off. I've had this 'intermittent' over heating problem for a while. It's a 74 cj5 with a chevy 350 and custom aluminum radiator, electric fan. I've thought in the past that maybe the fan is intermittently switching off (it is not connected for therm control so it should run all the time) but it seems that it is always on so I don' think that's the problem. I changed the thermostat out a while back and that seemed to 'fix' the problem, but now it creeped back again, so I flushed the whole system, replaced hoses etc. So MY question is....could AIR in the system cause intermittent over heating problems? I should have drilled the t-stat when I had it out on Saturday. One other note..when re-filling the system, I was surprised at how LITTLE coolant it held. I barely got 2 gallons (8 quarts) in it before it was 'full'. I've checked and rechecked after each short drive, and I've added maybe a couple quarts to keep topping it off. Since it's an aftermarket radiator, I really don't know how much it should hold, but I was thinking more like 15 or so? This also leads me to believe there may be air in the system.

Thanks,
Steve

 

the radiator at a minimum should have a core the same size as the cubic inches of the engine; in other words, the core should measure 350 square inches ( L x W); this doesn't include the number of rows, 2, 3 etc.
Novak has good cooling info on their site.
I'm not a SBC engine guy, but I don't recall hearing about any air lock issues with them.
Beside all that, just the normal things to check:
t/stat
rad cap
actual water temp with a thermometer
movement of water thru the radiator off idle
etc

 

Air COULD do this...but I don't think that's your problem.
How long has it been getting higher than average temps? In other words...did it just start out of the blue one day...or has it done it ever since you have owned it?

 

Kind of hard to pinpoint. I've had the jeep for about a year. It did it several times in the first 4-5 months, but there was a time in the winter (again, So Cal..so not REAL cold) where it seemed to run too cool. But then outta the blue, it'd heat up again. The first time it got 'real bad' was last February or so, we were out trailin and the temp started climbing, then got to the point where it began to boil over a bit. I shut it down, waited a while, and then drove it the rest of the day without a problem. When I got back from that ride, I went to town, got a new t-stat, and that seemed to fix it. But every now and then, it'll heat up again. I will definitely replace the t-stat again just to rule that out and also measure the radiator dimensions tonight based on the prior response to my thread.

Thanks for the help.
steve

 

Collapsing hose on the suction side of the water pump?

 

You would not by any chance be running a TBI on your 350 would you?
This is just a total shot in the dark here...Because you did not say what carb (or lack there of) you have.
The reason I even bring up the question is I had a similar problem with pick-up that I did a TBI conversion on. It took me forever to figure out what was going on...it would run 190 for months...then all of a sudden it would get hot...and it would not even be warm outside. I found that the closed loop was sending some incorrect info and would make the truck run lean every so often. Not bad enough to make it run poor...just bad enough to make it heat up. I hooked it to a wideband tuner...and waited for it to heat up again...Took a few months before it did it...but when it did...the Air/fuel went really lean.
I highly doubt this is your problem...just thought I would throw it out there because of the similarities.

 

As a matter of fact I AM running TBI. I converted earlier this year, however, the symptoms I described happend both before and after the conversion. I also replaced the hoses this weekend, so I don't think it's a collapsed hose. I'm going to replace the t-stat this weekend. Very strange!

 

Just throwing some things out there that have caused me some grief, do you by chance have a heat riser valve that is intermittently sticking or broken?
Something to share with my new jeep friends, I had a 1 1/2 ton truck for some years that would overheat and run rough for no apparent reason every time it was pushed hard ( but not outside what it should handle ). Everything was within spec from one end to the other, Drove us nuts for over a year until we replaced the exhaust system and found the problem by accident. The exhaust manifold on the passenger side had the chock hot air tube running through it, When we got the manifold off to put new gaskets on there it was. The manifold casting around the choke hot air system was bulged out on the inside ( a bad casting ) leaving a slot only 1/4 inch wide by 1 inch long for all the exhaust from that cylinder to get out.
We found another manifold and man did it run then!

 

Well now THIS is interesting. I do not have this specific problem as the V8 has headers, but there IS a 'pinch' in the cross tube that connects the right and left headers under the jeep. It appears that at some time (the PO) the front drive shaft 'hit' the pipe and pinched it. Now mind you, this is not in EITHER of the two main exhaust pipes, but rather in the tube that connects them together (to balance I think). Not sure if this would cause the problem, but the symptoms are EXACTLY like was described in preceding post...if pushed a little, it heats up...or if it sits at idle for a long time. But it does NOT happen ALL the time. I will replace the thermostat when I get back out to the river after Christmas and see what that does but since I've already done that once, I'm not too confident it will fix it.

 

Nope...it's just a balance tube...you could cap it off and it would not cause heating. Do you know what kind of fan you have? I know you said electric...but any idea who makes it or how much CFM it's rated at?

 

I should know but I don't. I think it's a pretty good fan. I need to find a way to be able to tell if it stays ON when it should. I half think that it is 'shutting off' intermittently, but I can't tell while I'm driving it. I thought about removing the hood and having a friend ride up there to watch it while I'm driving, but then I read the 'fan came apart' thread and decided against!!! (just kidding). Actually, I've thought about wiring a light or something that I could monitor from the cab. Might see about doing that.

 

:iagree: The balance tube ( or lack thereof ) would not cause the overheating. Is there some kind of Coolant Temperature Override ( CTO ) switch that activates the electric fan that could possibly be defective? I dont have to much experience with electric fans but I thought they had both high and low temperature sensors that controlled when the fan came on and off. Assuming everything else to this point has been ruled out.

 

Yeah...I'm thinking it's the fan too.
One way to tell if it's the fan would be to get out and open the hood when it's getting hot...if it's not running...then there you go.

 

Well now....THERE'S a hell of an idea Macgilacuddy! Did you see my 'tag line'....It's almost ALWAYS the simple things. Next time it gets hot, I'll LOOK at the fan....Doh! It really DOES seem like it's something like that. I don't believe the fan is hooked up in such a way that it senses heat and turns on or off. I believe it's hard wired to always be on, but I believe it DOES have the capability to operate based on temp. I'll definitely take a peek next time it gets hot.

 

Let us know what you find, Look and see if there is a CTO on or near the thermostat housing ( it could be on manifold elsewhere if yours circulates coolant ) that is disconnected, Maybe there was one and it went bad then the PO disconnected it and wired it direct.

 

So I'm not familiar with these 'CTO' switches. My manifold DOES circulate coolant, but I'm unaware of any switch etc near the thermostat. I DID run the jeep the other day, again a 'warm' day but probably only high 70's. It ran perfect, held 180, even idling in fast food line, but as SOON as I started up the grade to my place, it started creeping up toward 210 or so. The grade is pretty steep, but only about 3/4 mile or mile at the most. At the top, I have about another 1/4 mile or so to the house which is flat or down hill, but it really didn't come back down to normal in that amount of time. I DID check that the fan was still running when I got home. Unless there are any other suggestions, I'm going to swap the thermostat out on Thursday, probably drill a hole in it to eliminate the possibility of air in the system, and see what happens. I'm almost thinking the radiator is just not big enough to handle that motor. I measured the area of it, and it was something less than 350 (like 340 or something). Someone posted earlier that it should be at least as many sq inches at the ci of the motor.

 

I know this has been frustrating for you, Assuming the fan is constantly pulling a sufficient volume of air its starting to sound like the radiator is just to small or its core is partially plugged by deposits, Either way they will heat up under load.
I have had to replace three radiators over the years that had these same symptoms, All three had flow hampered by deposits building up in the core.
I am almost out of ideas unless there is a very lean fuel condition or timing problem.
Just for reference the core on my 55 Cj with the 134F-Head measures 16 * 16 and its three rows deep. I think I will measure the core on my Cherokee with the 360 tomorrow and let you know what it is.

 

Thanks Brian. I actually put in new thermostat today, after drilling a small hole to eliminate any 'trapped air' issues. I ran it a bit today, several times up that hill, and while it got above 180, not much. It WAS cooler today than the other day when it pushed toward 205-210. I'm pretty sure the radiator is gonna be the problem. I think it might only have ONE row. It's pretty thin. I'll get to test it out in the desert this week, so I'll know soon enough.

Thanks for all your help and suggestions! This forum is AWESOME!

Happy New Year!
Steve

 

For reference, the core on the radiator in my Cherokee with the 360 measures 25" wide by 16" tall. It is three rows deep.
I have seen several 25 * 16 cores two rows deep in Wagoners with automatics, I think the three row core version was part of a towing package.
And you are correct about it being a little cooler, It does not take much of a change in ambient air temperature to influence radiator performance, Especially if its marginal to start with like a partially plugged core.
Good luck and let us know what you figure out.

 

I would hate to have you just start throwing money at this...But....from your description...I'm kind of thinking that maybe it does not have enough fan. Too bad you are not in my area...I would give you a high CFM one to try. Or...you can go to a wrecking yard and find yourself an electric fan off of a 90 to 95 Ford Taurus...these pull A LOT of air (I think the Lincoln V6 had the same fan, but not sure)...In any event...You would have yourself a good fan.
And like Brian said, a slight change in ambient temperature can make a ton of difference.