Water will cool like anti freeze, just the same. and the proper mixture of antifreez to water is 50/50 as recomended by the jugs and such. I just buy the pre mixed, works fine.

What are you useing to flush the system? Did you buy a flush kit from parts store?

Mine had me put in a T bracket on the hose to the heater core, and then i drain the coolant that i can, then, close valve, open radiator cap and install nozzle, and plug the water hoze into the T, and let it flush out all the old stuff, then it has me start the engine while the water is going in and comming out constantly.

This seems to me, would clear out any air pockets inside the engine.

Isn't standard heater core temp 180?

 

Thats the weird part, you siad in one post i believe, that you slowed down on backroads and it dropped? This makes it weird, since we all know that at 60 we have more air flow then even our fan can provide. The thing we all need to figure out here, is what is happening at 60 that foes not happen at 50. Or is it purly timing? If you drive it for an hour at 50 will it get hot? Or is it only at high speeds?

have run into this before, and you may need to take a couple of well planned test runs. really isolate the problem. Other engine problems could be the cause, and it could ba as simple as a inner fender or air damn out of place, and the back pressure only shows at certain speeds.


But, check this, if its not overflowing at 230, is it really overheating at all? Got a friend with a lazer thermometer? check it at vatious times various places, and note the temps.

Never seen it on these engines, but some gm v6 are very air prone, you can try what i do with them, and pull the t stat. fill the rad till you see it rising in tje block, when the block is full( dont overfill, getting it dry to reseal is tricky) replce t stat and housing, then start and fill.

How is the heater working? does it get hot or cold when this happens?

And lastly, when you say you replaced this stuff, was it new, or did you get it from salvage? I have this alot since i wrench out of a junk yard, sometimes i put on stuff that is as bad as what i took off.

I know this is alot, but this is not a problem that you should be having.

 

To save you from rereading my posts, I'll repeat my problem and what I have done. My '91 e-250, 6 cyl auto, begins to overheat after I've sustained speeds of 60-70 for 15-20 miles depending on which direction I go (hills?).
My radiator is 1 year old. There was no stat in when this problem began. I've replaced the : pump, fan clutch, belt, cap, lower hose (has spring in it) and replaced stock gauge with a mechanical one. I get off of the highway when it hits 230 degrees, although last time it hit 240. the cap has not released water into the overflow on any of these overheats. When I lower my speed the temp goes down. I ran two block gas tests on it, the second one on gases released into the overflow bottle during an overheat. Negative. I ran a batch of cooling system cleaner thru it the other day. The new lower hose didn't come with a spring, so, today I drained the system to put the old spring in it. Even though the radiator had stopped draining for some time, when I pulled the hose off of the radiator a quart, or, more of water came out, that had to be above the level of the petcock. Does this indicate anything?
I filled the radiator up to the bottom of the neck and watched as it came uo to temp. The water level kept rising, little bubbles would appear and a couple of big bubbles, then the water would drop. I thought the bubbles were probably air being displaced, but, I performed a third block gas test. Negative! Suspicious of the blue liquid in the test kit, I tested the exhaust at the pipe and it turned yellow!
I topped it off and came in to type this.
Last week I took a 20 mile trip and kept it between 50-60 and no problem. Tomorrow I am taking a 100 mile trip. I will see if I can make it at the lower speed, but, I might try 65 if it behaves.
any more ideas?
lloyd

 

The fact that you're not getting any overflow at or above operating temp is a BIG clue. It's abnormal for a hot engine not to overflow.

What kind of water pump did you put in? If you used a cheapie, it might be cavitating*, which can lead to all sorts of cooling system problems, including the ones you're experiencing.

The fact that it only overflows at higher speeds would seem to indicate an airflow problem, though. My best guess is that you actually have two problems going on (which is why this all seems so weird and unexplainable). The airflow problem doesn't have anything to do with the lack of overflow, and vice versa.

My advice, if you're tired of dealing with it, as I would be if I were you, is to talk to several mechanics that you trust in your area, and get a consensus as to who is the best cooling system guy in your area.

Mechanics don't like to admit it, but they're not all experts. Some of them know a lot about some systems and cars than they do other systems and cars, some of them know very little altogether, but very rare is the mechanic who knows everything about every car.

* Cavitating is the same thing that happens to submarine propellers in the water. The screws turn so fast that small pockets of air form behind the blades and then immediately collapse. It makes a sub very easy to trace via sonar because of the noise of collapsing bubbles. It also physically damages the blades when it's sustained. The very same principles apply to the blades in your water pump, damage and all.

 

Check your temperature sensor. Maybe it is not overheating at all. I believe the Haynes manual tells you the specs on the temperature sensor. Of course that does not explain why it cools down when you drive slower.

I once had a problem with my Honda Accord doing the same thing. It was even losing power at high speeds. Turned out the valves were tight (don't think that is the problem though, your truck has hydraulic lifters right?). It could be an engine problem not a cooling problem. Maybe the valves are floating from weak valve springs.

 

I was thinking a cavitating water pump but that one was taken already . Has the belt tensioner been checked? Just a thought.

 

i had this same problem with a 302 and i replaced everything you have and my problem was the radiator. I took it out of the vehicle, laid it flat on the ground left the cap on and put water hose in the return(bottom)outlet and it puked a whole lot of nasty black stuff out the top. I didnt see where you mentioned anything about taking it out and flushing it backward. My bronco only overheated at inerstate speeds(60-75)but would not at 55< I was also puzzled, after new clutch fan, thermostat, water pump, and sending unit. Afterall youve been through try this one too.

 

I just fixed the same problem on my 89 f150. It turned out that my radiator that U had bought just under a year ago was clogged and leaking. Replaced it and no more overheating. Just an idea.

 

I Took a 200 mile round trip from Hartford, CT to Keene, NH today. On the way up I kept it at 55-60 thru most of the first half of the trip. I moved it up to 65 for the last 10 miles or so of the highway part. No problems.
On the way back I kept it at 65-70. After about 30 miles of climbing hills ( the Berkshires) it went from 190 to about 210. Slowing down stopped the temp from climbing, but, it did not drop much as I was still climbing hills. When things leveled out, it went back to the 190-195 range.
I think my running a batch of cooling system cleaner thru it is what improved the situation and I will do it again and try the thing with the radiator.
Thanks to all
Lloyd

 

I have a sugestion if I may....if you are over heating or running a higher temp at higher RPMs then you may have a restricted EGR valve.....this would casue higher combustion temps and cause the coolant issues you have described at low speeds the egr is closed low rpm {lower vaccum} and higher speeds egr is open {higher Vaccum} as recirt gases enter the intake they lower the combustion tempature....hope this helps I went through the same problem replaced all componets of cooling system only to find out that it was the egr causing my heat over load on cooling system...

 

Same way with mine and it was the radiator. If you flush it like mentioned above it wont cost nothing but a bit of your time, considering you arent running coolant. I went through the whole replacement thing myself and it was the clogged radiator. Egr's are expensive though, if the back flush on the radiator doesnt work then go to step 2. Havent you spent enough on replacement parts to keep coming up with the same thing (still overheating). If you ran system cleaner threw it and it seems to be doing better then it seems something is blocked.(radiator!) hope i can help again. good luck.

 

heres a cheap trick i learned , get some muratic acid from the local home depot/lowes REMOVE YOUR RADIATOR lay it flat on a table mix a 50/50 solution water, acid, put in radiator swish it around, (make sure you cover all holes, as not to get any solution on you!) let it sit for a hour or so then dump out the solution and continue to rinse and swish with water... when you see a lot of white stuff comming out your doing it right..
P.S.> never use "STOP LEAK'' UNLESS YOU LIKE REPLACING RADIATORS EVERY YEAR OR SO .....good luck! the ford 300>6 is a very good engine, i maintain them every day. if i had to do it again i'd replaced my 302 in my bronco with a 300/6 rather than a 351...ford did'nt screw around with the 6 as they did with the W series...