overheated 4.0

[stx4.0]

Ok I need a little help with this one or lots depending.I came across two early 4.0 powered vehicles cheap.One is a 93 explorer sport and the other is a 94 ranger 2wd with the 4.0.I got them from a guy that said he overheated both of them and wasn't willing to spend the money repair them.Since I can do the work myself I bought both.The explorer had a bad water pump failure and I tore into it and took the heads to a machine shop.The guy there told me the heads were not warped but the right side had a bad crack so I bought a set of alabama heads.The block I checked myself with a straight edge in the vehicle and it looked fine.The guy at the machine shop told me the heads would warp way before the block.I put the new heads on along with a new thermostat anitfreeze etc and it still overheats and I mean in a bad way like there is no coolant at all in it.The radiator was cleaned out and I was told it wasn't dirty at all and the clutch fan seems to be fine as well although it is not new.I am stumped on why this thing is overheating so bad.I thought the gauge might be bad but checked it with a thermometer and it definitely is getting hot..I am thinking the only thing it could be is the block.Is there anything I might have missed?The thermostat was installed correctly so no issues with it being backwards.I do not want to tear into the ranger and have the same thing happen.

 

[shucker1]

I'm not a 4.0 expert. I have a 5.0 V-8 but I have read other post where you have to burp all of the air pockets out of the 4.0 to get any water circulation.

You might try and search on that thread.

Of course the belt is routed correctly and the pump is spinning the correct way?

 

[stx4.0]

Your right,if you don't get the air out that can be a problem and the 4.0 is known to be a real pain to get the air out.I always fill them thru the top heater hose connection on the lower intake so that it bypasses the thermostat and easily pushes the air out.I've never had a problem that way with getting the air out and good point about the pulleys and belt direction but yes I checked all that before ever firing it up to make sure it was correct and it is.I am kind of leaning towards the block being warped but I did check it and it made sense that the heads would warp before the block since the block is alot thicker but it had been hot for sure.The crack in the one head was huge.Its just been real baffling trying to figure out why it still overheats.

 

[FR-425]

Coolant in the oil?

 

[vq5speed]

What are Alabama heads? just the name of the machine shop.. what you mean you tore into the water pump. Did you replace it with a new one.

 

[stx4.0]

No coolant in the oil at all.Before I tore the engine apart the cylinder below the where the head was cracked was filled with coolant so I already knew i had a crack.I was just surprised they both weren't and very surprised they were not warped.

Alabama cylinder heads makes new heads for 4.0's that are thicker castings and do not crack as easy as the originals.I've never really known the 4.0 to have that problem like the 2.9s did but I got them cheap so I used them but that's where "Alabama heads" comes from.Actually I shouldn't say they make them as I heard they are made in austrailia but they are the ones that sells them.

The water pump of course was replaced with new as it was the part that failed that caused the overheating in the first place.

 

[vq5speed]

So exactly how does it still over heat. The temp gauge goes into the Red and the engines stalls out?

 

[stx4.0]

No,I don't let it go that far as I don't want to ruin the new heads or anything else,I just watch the temp gauge which is what made me check with a thermometer.I've ran it several times just to make sure there were no air pockets hidden but like I said it acts like it has no coolant at all in it,once the gauge starts climbing it races towards hot like there's nothing in it.The pump does circulate the coolant.I have felt the hoses while I had it running.I've checked about everything I can think of other than pulling the engine out and having the block checked.

 

[natenkiki2004]

What thermostat did you use? For ***** and giggles, pop the old one in or get a new one, different brand. Could be that it's just not opening at all.

I've grown quite partial to the Stant SuperStat I put in. It gradually opens the valve as the temp warms up unlike the one that was in it before. The old one would wait until the temp got up to the higher end then open, over-cool, heat up to the top end, open and cool. There were probably 2-3 heat cycles before it evened out. The Stant eliminates that and in my eyes the less heat cycles, the better for the heads, especially if you're running a factory one (I know you're not... just saying for sake of argument though).

 

[stx4.0]

I tried all that and even tried it without the thermostat in and then was told that would make it overheat even faster as it would have nothing to slow down the coolant flow through the radiator.I dont know what the one I bought was called but it was from stant and was the "good one" per what the parts guy said.I dont like using cheap parts and bought the best one available.I am thinking something is messed up with the block but can't think of where it would be other than the deck surface and it seemed to check out fine.

 

[shucker1]

Have you tried double checking stuff with a IR temp gun? You said you used a thermometer, where?

Perhaps since it over heated real bad last time, the factory temp sensor in the block is damaged and giving trash readings?

 

[stx4.0]

A friend of mine used his thermometer at the radiator.It is some kind of snap on part he uses at his business.It is probably called something else but thats what it is used for is check coolant temps.I watched my gauge as he checked the temp as it was running and he had me shut it down.My gauge was reading it right.Yes I double checked everything I could think of and triple checked others like the head gaskets before the heads went on.It is weird gremlin for sure trying to figure out if I missed anything.The guy I got it from I guess was out in a snow storm and couldn't stop.He said he drove it about 10 miles with the temp gauge pegged and knew he likely did it in.It only has just over 100k miles which is low for the year and really low for some of the 4.0's I've seen.When I did a compression test after the new heads were installed all cylinders were 165 to 170 so I would hate to have to tear the engine back apart and will likely just change the engine if I can't figure out where the problem is.Its odd to me that the heads did not warp but just had the one that cracked.Being pegged for that long I think everything should have been warped.

 

[natenkiki2004]

Compression sounds good. Removing your thermostat would actually make the engine run cold. It would get full flow of coolant and never heat up. If your engine still overheats with the thermostat removed, there's gotta be some kind of blockage. I don't imagine the block would warp. Being a v6, they're pretty beefy casts. These blocks have been built up for race engines running a turbo and all kinds of power.

 

[stx4.0]

Thats what I thought also but I had so many people call me an idiot for doing that including the guy at Ford.They said by removing the thermostat the coolant does not have time to lose its heat through the radiator and cycles back into the engine too fast to pull the heat out which in turn causes it to overheat alot quicker.I guess that was common knowledge I missed out on years ago.The thermostat allows a slower steady flow so that it has time cool off as it flows through the radiator.

 

[natenkiki2004]

I thought it was common knowledge that stuck-open thermostats cause vehicles to never warm up and get no heat out of the heater?

You need an initial restriction to warm up quickly then once at operating temperature, open to keep the temp from rising. To my mind, there should be more surface area in the radiator than there is in the engine so the rad should cool quicker than the engine heats up. It would only make sense from an engineering standpoint for a radiator to cool faster at full flow than an engine can heat.

Anywho, I'd still try it and see if you get a different reaction. If not then there might be a restriction somewhere. On the 4.0L, the rear coolant passages in the lower intake are blocked. There's only flow in the front 2 passages. However, with the temp sensor right behind the thermostat, it seems odd that there would be a restriction. If you had a restriction, I would think that you wouldn't see high temps on the gauge.

Have you seen any bubbling in the rad cap or reservoir with the engine running? I'd imagine a crack in the block more likely than warpage. The crack might be down low in the cylinder and not show on a compression test.

 

[stx4.0]

There shouldn't be any restrictions as I know the orig cause of the overheating which was the water pump going bad,however when I had the heads off I did flush everything out that I could.Looking down in the water jackets with the heads off everything looked real clean and the coolant/radiator was fairly clean as well.I think you are correct if there was a restriction the temp sensor would not allow the gauge to show temps as there would be no coolant around it.I never really thought about a crack being down low in the block but that would still allow coolant to get into the oil and I would have cross contamination.So far everything has stayed clean and the exhaust has looked normal.I have not noticed any bubbling going on either.My machinist said same thing about a crack over warpage in the block which is what my heads did also and that doesnt make sense to me.I thought anytime the heads got that hot they always warped but neither one of mine were.

 

[natenkiki2004]

Good observation, with a crack, you would have cross-contamination. So, no contamination, no exhaust gases leaking into the coolant, new heads, good compression...

Hmmmm. Your friend measured the radiator, what were the temps? I'm halfway wondering if it's just your temp sensor being fried. Did you get a new one?

 

[stx4.0]

It sailed past 235 degrees when I shut it down.I didnt want it to be that hot with new heads being on it.We have checked it several times just to make sure there was no hidden air which I was sure there would not be because of how I filled it plus ran the heater the whole time.I am probably going to put a new clutch on the fan just to eliminate it from the list plus they don't cost that much.Yeah i would have thought the temp sensor would have been fried too but it is still working.I guess being up high and being in aluminum kept the bad heat from damaging it.One odd thing the guy told me about it was he said thats the only vehicle he ever had that he could go outside when it was 0 degree weather and about 2 minutes after he would start it he would have heat.I dont know if i can believe that or not but he had no reason to lie about it..He said the temp gauge would move about a half inch up and thats where it would stay even in the summer on the hottest day with the a/c running.

 

[shucker1]

As a quick test for the new thermostat you have you could pull it out and put it in a pot of water of the kitchen stove with a thermometer in there as well.

See if it opens at the stamped temp and how wide it opens. You could have a bad one.

It is possible to move water through a radiator or heat exchanger too fast and get reduced cooling efficiency.

You wind up with something called a boundary layer on the tube which stays cold while the inside faster moving medium stays hot.

Most industrial radiators and heat exchangers are built with turbulators which helps slow the flow and increase cooling effiency.

 

[stx4.0]

That was the point I made earlier when someone asked if I took it out to see if it overheated.I did put it in a pot of boiling water to make sure it worked but I always do that before I ever put them in.The 4.0 is kind of a pain to change them out so definitely wasn't putting that one in without checking it first.I have tried about everything I can think of other than a new radiator and clutch for the fan.Im pretty sure neither of those are the issue.