A very stubborn overheating issue .. HELP!!!

Here are the quick facts:

1994 Mazda B4000 4.0L, 2WD, 5-speed, 109k miles on it. Well maintained.

Runs fine, has not lost any power at all since overheating issues started.
No visible oil in coolant.
No visible coolant in engine oil.
Does not loose coolant.

Radiator is 3 years old. Still looks like new. Clean inside, except some rusty looking gunk built on the radiator cap.
Radiator hoses are 2-3 yrs old.
No coolant leaks anywhere.

Originally, Fan clutch, fan blade, thermostat and antifreeze were replaced in 2011, only 10k miles ago. (yes, this truck is not driven much)
I used NON-OEM parts.

Fast forward to few weeks ago, .. we noticed that when we drove the truck in heavy traffic for longer periods of time... the temp gauge will start to creep up. I had to pull over once because it was going pretty high. The rest of the short local drives, there were no issues.
Then, on a recent trip to local recycle yard, it started to overheat again, going uphill.... going downhill and...even going 55mph on the freeway... temp was on the high side.

This is when i decided that it is time to replace some cooling parts.
I bought and installed a brand new water pump from Napa, new thermostat from Napa, and new fan clutch from Oreilly Auto parts (Murray brand).

Drained the radiator, replaced pump, thermostat, fan clutch, and one of the hoses going to heater core. Put brand new 50/50 coolant mix. I burped it all and took it for a drive.

Well... truck overheats again. City driving... or highway driving... it gets above middle level on the temp gauge. If i let it go close to "H", i start to hear/see hissing and some steam from the radiator cap. The gauge is not lying when it shows close to "H". It does overheat for real. I burped it more... 3 or 4 times. Still no luck. If i drive it for more than 10-12mins or so, it starts to go above mid level on the temp gauge, slowly.

So... i decided to completely remove the Napa thermostat, since i read about crappy new non-oem thermostats, getting stck closed. Same result. It still gets hot. :grumpy:

****
Something VERY interesting i noticed is that the rubber hose that goes from the new water pump to the heater core, almost DOES NOT have any coolant coming out of it when the truck is running. ?!?!?! I removed it from the heater core with the engine running and it was barely dripping antifreeze. Why is this happening?
I am pretty sure the water pump is moving because i can see antifreeze circulating inside the radiator when the engine is running and i remove the radiator cap.

I noticed that the new fan clutch i installed is spinning a bit too easy...regardless if the truck is cold, warm or overheated. It does NOT seem to lock at all - ever. So, today i went to parts store and requested a replacement for it. Got the same brand (Murray), another new fan clutch. This one is stiffer, but it still does NOT lock completely when the truck is hot and the truck still overheats slowly, like before.



Basically, to summarize, i've replaced the fan clutch 3 times now. I have a new water pump installed, newer radiator, i am running with no thermostat at all, and my truck is still slowly overheating... and for some reason my heater core hose does not get any pressure/coolant !?! Yet, I do get heat in the cabin and the AC seems to work fine.

Btw, using a garden hose, i ran some water through the heater core while it was connected on the other end to the engine and water did come out of the water pump side heater hose. No clog detected. Yet, when the engine is running, nothing comes from the heater core hose attached to the water pump. :shrug:


What am i missing here?! I've been dealing with this old truck for 10 days now... and i am pretty much running out of ideas. :shrug: Any help is well appreciated.

Thanks!
Dan

Please understand that I am not a mechanic and do not approve or disapprove of any of what I am posting. But I did do some searching on the net and found these answers. It sounds to me like you have some clogged coolant passages that need to be cleared. How to do that seems to be a matter of opinion, but here or some of the options I found that may give you some relief. But remember, this advice isn't from me. I'm just passing along what I have found. Good luck.

+1, but if you have no choice, then a MASSIVE ncooland flush is in order, remove the radiator and check condition, if shot, replace.
Once Radiator is back in, undo the bottom of the radiator for draining, place hose in the top, fill radiator with hose still running, and fire up the engine with the heater set to maximum.
Now it's just playing the waiting game, let the engine run, sit in the car and keep an eye on the temps, they should rise to about half of normal, as it's getting stone-cold tap water barrelling through it.
The heater should warm up a little as well, but not be piping hot like normal, again because your flushing decent amounts of fresh clean water through it.
Keep an eye on the water rubbing out of the bottom of the radiator drain hole, it should eventually go clean, and this is what we are looking for.
Once it's gone clean, close off the bottom of the ratiator and fill with pure concentrate coolant.
reason for pure is because the block and heater core already have about 4 litres of water in them, and the radiator will have 1 litre or so in it, out of a 6 litre system, so pure concentrate is the best.
Do this once a week for 3 weeks and the concentrate should ahve disolved most of the rust in the block.
Be aware, if the block is like this, the water pump is going to be almost stuffed, the any external pipes will be pretty stuffed, and it's going to be a matter of time before this car gives you grief.

I also found this website on the subject: http://liquidintelligence115.com.au/products/engine-cooling-system-cleaning-kit


I also found this on a boat forum:
Re: Muriatic acid for cleaning the cooling system on a fresh water engine?
for cleaning the cooling system on my car i usually use oxalic acid. it has never hurt the radiator, hoses or engine parts (both iron and aluminum). i get it at the hardware store by buying wood bleach. if you remember the good ol days of car repair there was a product that had a paper tube with the radiator cleaner in one end and the neutralizer in the other end. the cleaner was oxalic acid. the neutralizer was baking soda.
if you can't find oxalic read the genesis post about cleaning the cooling sytem with phosphoric. i have also used that on car cooling systems with no ill effect.
muratic is very serious stuff. the fumes coming out of the cooling sytem can definitely kill you. have lots of fans going to keep fresh air flowing. and wear a respirator. if you are going to use muratic below decks you might want to have paramedics standing by to resuscitate you.
Re: What to clean water passages and cooling system with?

and this also:

i have heard baking soda is great, put like 2 table spoons in the radiator and drive the car for like a week and flush it all out, all the rust should come out.

OP , do you have an overflow tank ?

Mickey Bitsko said:

OP , do you have an overflow tank ?

Click to expand...

Yes, i do have an overflow tank. It's the original OEM tank.

I cannot be 100% sure that there is or isn't a clog somewhere, but i also know that the coolant in my car was only few years old with very few miles on it (10K) since the last flush. I do not see any rust or any other strange color in the antifreeze.
The radiator is not old and when i run water through it, it comes out very clear.

I just bypassed the heater core completely.
I also put another brand new fan clutch.
Thermostat is completely removed from system so it cannot be suspected.

I drove the truck, and it is still running hot(warmer than normal), when i drive it for a longer period of time.
I can drive it on the freeway for 4-5 miles, do a bit of stop and go driving, ...but after awhile, eventually the temperature will start to creep up towards "H" on the gauge. Slowly.

I guess, the good news is that it does not overheat fast.
It does it mostly in city driving...stop and go type of situations.

This is the 3rd fan clutch i installed in this truck in the last 2 weeks. I refuse to believe that all 3 of them are defective.

The water pump is the only new thing that i have not replaced. But i really cannot see how such a simple, brand new, water pump device can fail.

I am really running out of ideas here....

Since you are running out of things to check I suggest this.

I would pull out the spark plugs and look at each.
Light brown coloring on white electrode is what you want to see.
If a plug looks "clean" you could have the start of a cracked head(between valve seats, 4.0l design issue), or head gasket leak
You can skip the above and go right to the test.

What happens with a cylinder leak is the cylinder pushes "air" into the cooling system when it fires, which collects in the head cooling passages and can temporarily block coolant flow until it is pushed out and eventually ends up at the top of the rad and is pushed out into overflow tank.
There would be some coolant loss but not much in early stage, later stage would show white exhaust "smoke".
The result would be increased coolant temp.

You can do "the glove test", it is free and definitive for cylinder leaks into cooling system.

Cold engine
Rad cap removed
Coil pack disconnected(you want a no start)
(Spark plugs in place)
Remove overflow hose and plug it's opening in rad cap seat

Put latex glove over rad cap opening and seal it to rad with rubber band, balloon or condom also works

Crank starter motor/engine and watch glove, if it starts to bounce then you have a leak.
Each time that cylinder is on it's compression stroke glove will bounce.

You can ID the leaking cylinder by removing spark plugs one at a time and cranking engine, when glove stops bouncing last plug removed was the one with the leak, reinstall plug to confirm.


A lean fuel mix will also cause engine/cylinders to run warmer, but..........you would getting pinging/knocking when accelerating.

Have you pressure tested the cylinders, I have a 2.3L, had a crack between the valves on cylinder 1, ran good, but would run hot due to exhaust gas getting pushed into coolant (and when I would shut off truck steam would run out of tailpipe for 2-3 minutes)... replaced head, runs great now. Do you run 50/50 mix antifreeze? You really need a thermostat, even if it's a 180 degree one.



https://youtu.be/5aCQbo0Ccp8

SAMSUNG say whaaaaaat?

Here is an update...

** I did the "glove test". When the engine was cranking, the glove did not even move. There was no air coming out of the radiator fill neck. None! I tried this multiple times.

** I rented a radiator/cooling system pressure tester tool. I connected the tool to the radiator neck and i pumped close to 17 psi of pressure. Looking at the tool gauge, i lost only ~1/2 psi of pressure after having the system pressurized for TEN minutes or more. No hissing and no obvious leaks anywhere.

** I also rented a cylinder compression test tool. All 6 cylinders gave me 150 or more of pressure....with no significant deviation between the different cylinders. This is well within the factory specs.

So, based on the results from the above 3 tests, can we conclude that my head gasket is fine and that my engine does not have any cracks?? I would hope so. Or is there another test i can try?

Now, the question remains... why is my truck running hotter than normal? I drove it again tonight, for about 10-12 miles... city streets and highway. I did not overheat but after the highway run, in the city...after some stop and go, the temp gauge started to SLOWLY climb up above the middle mark, toward the "H". As i drove it more, without stopping often, the gauge went back to the middle (normal).

Also, i noticed that only once today, in the afternoon heat, when my truck was running a bit hot again, i heard the fan making a "roaring" sound when i revved the engine. It did it for 1-2 minutes only. Then fan got quiet again, as if the truck was not hot. When i turned the hot engine off, i tried to move the fan blade, and it was moving. Not doing full revolutions or anything, but i could push it and it would go for 1/4-1/5 of a turn.
I would expect it to be locked, not moving, or barely moving if the temp gauge shows above the middle.

Isn't the fan supposed to make a roaring sound when the fan clutch is fully engaged and the fan runs with the engine rpm?
Isn't it supposed to engage every time the engine gets hot and make that roaring sound?
Well, if answer is yes, mine does not do that.... like i said, only very occasionally.

Which makes me suspect the fan clutch AGAIN, being bad/half effective!!
This is the 3rd new non-OEM fan clutch i have installed.
Could the fan clutch still be my problem after 3 new units?


Can the fact that i removed the thermostat completely be the reason for overheating as well? I don't see how wide open flow of coolant can cause overheating... but who knows. Am i missing something?

Yes, thermostat slows the flow of coolant thru the rad allowing for better cooling.

Yes, puzzling issue.

Fan clutch only really comes into play when stopped or going very slow.
So symptom of bad fan clutch is rising temp gauge at stop lights and then temp gauge drops when moving again.

If you see overheating while driving then it would be something else, because you have enough air flow thru rad, fan isn't really doing anything above 30mph.

But low flow of water pump or clogged up rad can have the same symptoms, temp rise when stopped then temp drop when moving again, so not a black and white symptom.

Have you tried running it with the radiator cap loose? Have you replaced the radiator cap?
I had a issue with my 2.8 and what I found was the block was full of rust what cured it was pulling the water pump and spraying high pressure water in the block through the thermostat housing hole and the water pump holes, at the same time rod out the fittings for the heater hoses as well as the bypass circuit. A small leak in the head gasket can also cause the system to go high pressure. Run it for a while with the radiator cap off if you keep getting bubbles you probably have a cracked head or leaky head gasket.

Not sure on the 4.0 but the 2.8 is hard to burp I found adding the radiator flush fitting on the heater hose on the intake manifold and while the engine is running pour water in the fitting until it comes out the radiator cap and quickly put the cap on the fitting.
http://cgi.ebay.com/ebaymotors/Prestone-Antifreeze-Flush-N-Fill-Coolant-Kit-Fits-Most-Cars-Trucks-/391150982375?hash=item5b126a54e7

Oh yea hold the fitting up above the top of the radiator!

get a coolant system cleaner and a back flush kit. run cleaner through system as directed, then install back flush kit and follow directions. also try making sure all of your hoses are in the right places, that's all I can tell you. I have the opposite problem, damn gauge will barely get into the normal range and not much higher, and this is after I figured out that the heater hoses that were on the water pump and thermostat housing were backwards. it was worse before that.

I was going to suggest the same thing. I did not see a mention of using a flush when you replaced the coolant. I always use a chemical flush when changing coolant. Also there are anti-freezes that are not compatible and can cause a blockage.