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webt to get the emissions testing done and got turned away for a fluid leak - transmission pump seal is leaking hard
about ¼ of the way home the needle hit hot and I pulled off the road to find black water gushing out from the radiator cap and bubbling into the expansion tank.
I don’t see oil/rainbows but it’s certainly dirty water
How long have you had the truck
and
How long has this been going on?
1990 F250 with the 460 big block, owned it since monday, its happened twice (ive driven it twice) - 1st time was within 4 min of firing it up and driving but it was only firing on 4 pots...
This time, now that the motor is running on all 8 cylinders - i let it idle for 30 min, no worries - swapped some speed and ABS Sensors then went to get the emissions done - 11 miles each way.
Stopped on the way to get gas so add mile for the detour.
Didnt over heat until the way back and its 102 out.
Does the fan come on at all? It will be a hydraulic fan so it should turn on when you first start the truck, and when it gets hot out.
Your radiator could be plugged up, who knows how long its only had straight water in it. I would flush the system thoroughly and fill her back up with antifreeze. I keep my mixture a little rich around 70/30, but 50/50 is ideal. Your thermostat could be having an issue, like stuck closed or just sticking in general. Your water pump could be rusted out. A good way to check this is to let the engine warm up and grab the hose that goes to the top of the radiator, you will have to wait a couple of minutes, but it should pressurize pretty strongly. I would also see if you have any codes.
My cooling system had water with no antifreeze in it for a while and I can some rust remover through the system and then drained it, and repeated a couple of times.
Another thing but your belt routing could be backwards or the pump could be spinning the wrong way, just a theory.
Does the fan come on at all? It will be a hydraulic fan so it should turn on when you first start the truck, and when it gets hot out.
Your radiator could be plugged up, who knows how long its only had straight water in it. I would flush the system thoroughly and fill her back up with antifreeze. I keep my mixture a little rich around 70/30, but 50/50 is ideal. Your thermostat could be having an issue, like stuck closed or just sticking in general. Your water pump could be rusted out. A good way to check this is to let the engine warm up and grab the hose that goes to the top of the radiator, you will have to wait a couple of minutes, but it should pressurize pretty strongly. I would also see if you have any codes.
My cooling system had water with no antifreeze in it for a while and I can some rust remover through the system and then drained it, and repeated a couple of times.
Another thing but your belt routing could be backwards or the pump could be spinning the wrong way, just a theory.
Fan is always on, so to speak, I’m in a hot climate so assume that’s normal - the top hose is rock solid when hot.
im going to follow your advice and flush as much crap out as I can, replace the thermostat with a 180° one and then add 50/50 coolant mix once clean water comes out. I’ll also replace the leaking bypass pipe with generic hose.
100%, What Truckbuck said, since you have no history on this thing,
Very through Flush, Change all other fluids before you drive it again. This includes flushing the brake lines, power steering, trans fluid and filter, some will argue not to do the trans, Do your research on this one. Diff fluids and of course engine oil. If the radiator water looked that bad, my guess it the rest of the stuff was probably not well maintained either.
100%, What Truckbuck said, since you have no history on this thing,
Very through Flush, Change all other fluids before you drive it again. This includes flushing the brake lines, power steering, trans fluid and filter, some will argue not to do the trans, Do your research on this one. Diff fluids and of course engine oil. If the radiator water looked that bad, my guess it the rest of the stuff was probably not well maintained either.
Brakes - check! DOT4 and new bleed screws…
Transmission - need to swap to the spare as this one doesn’t have a speedo drive gear
I don't want to crush your hopes, but this is my full story.
The truck never had an issue with overheating but the coolant was rust colored, and the overflow had literal debris in it. I ended up having to take the engine out, along with the radiator, but there was psychical debris in the cooling system probably 2 cups worth of hard water, and rust chips. I hope yours isn't that bad because I had to replace the entire cooling system, along with pulling out the freeze plugs and putting the block through the jet wash a couple of times.
I am glad you are getting somewhere, you can seal up the fan housing to the radiator to make the fan more efficient. I recently picked up a "high flow" thermostat off of rockauto and am going to install it, might be something you want to look into if this issue is still prevalent.
Chrisfix has a good video on flushing your coolant system. POR-15 makes a pretty good rust remover, although I would be careful because some of these products will eat rubber.
Make sure you "burp" the cooling system to get the excess air out of it.
I don’t see oil/rainbows but it’s certainly dirty water
suspect the PO filled with water and not coolant
no “mayonnaise” in the oil filler cap
But does it still run toward the hot end of the gauge?
I’ve never seen black water come out of the radiator. Are you sure that isn’t water and ATF?
Not a problem if the system is working properly. Antifreeze/coolant will help prevent corrosion and lubricate the pump.
That occurs because of moisture in the oil from short trips where the engine doesn’t not get up to temperature long enough to get rid of the condensation.
Originally Posted by Truckbuck
Does the fan come on at all? It will be a hydraulic fan so it should turn on when you first start the truck, and when it gets hot out.
Another thing but your belt routing could be backwards or the pump could be spinning the wrong way, just a theory.
The engine fan is not hydraulic. It is mechanical. Where are the hoses connected to the fan?
How could the serpentine belt be routed backwards?
Originally Posted by Aedhasdad
I’m going to follow your advice and flush as much crap out as I can, replace the thermostat with a 180° one and then add 50/50 coolant mix once clean water comes out. I’ll also replace the leaking bypass pipe with generic hose.
No. The stock replacement thermostat is 192/195°. That is what you should use for the computer to go into closed loop mode.
It is a pressurized system. You cannot have a leaking hose or anything else.
Originally Posted by Aedhasdad
Brakes - check! DOT4 and new bleed screws…
Transmission - need to swap to the spare as this one doesn’t have a speedo drive gear
DOT 3 just as it states on the reservoir cap.
Why do you need a speedometer drive gear? Is the truck two or four wheel drive?
But does it still run toward the hot end of the gauge?
I’ve never seen black water come out of the radiator. Are you sure that isn’t water and ATF?
Not a problem if the system is working properly. Antifreeze/coolant will help prevent corrosion and lubricate the pump.
That occurs because of moisture in the oil from short trips where the engine doesn’t not get up to temperature long enough to get rid of the condensation.
The engine fan is not hydraulic. It is mechanical. Where are the hoses connected to the fan?
How could the serpentine belt be routed backwards?
No. The stock replacement thermostat is 192/195°. That is what you should use for the computer to go into closed loop mode.
It is a pressurized system. You cannot have a leaking hose or anything else.
DOT 3 just as it states on the reservoir cap.
Why do you need a speedometer drive gear? Is the truck two or four wheel drive?
Im in AZ and I swapped all the Thermostats to 180f - 62 Jag and a 1980 Triumph Spitfire - made both run cooler.
I didnt know that would be a thing for a Truck.
DOT4 is DOT3 with a higher boiling point.
Speedo Drive gear on the output shaft turns the speedo cable - i need this to avoid tickets from the police, i also need this to tell the computer how fast i am going so it will change gears. ATM - D = 1st only, i can manually shift to 2nd with the column selector, or 1st again.
Last edited by Aedhasdad; Aug 15, 2025 at 06:05 PM.
Last time I checked a ‘62 Jaguar and a 1980 Triump are not computer controlled EFI but your truck is.
Motorcraft DOT 3 probably has the same boiling point as DOT 4 . I use Valvoline DOT 3 because it has a higher boiling point than other DOT 3 stuff on the parts store shelf. None of that is a problem if you occasionally flush the old fluid out of there.
On a four wheel drive truck the speedometer cable is in the transfer case but you never answered my question if you have a 2wd or 4wd truck.
Incidentally, the fluid I collected from the system when draining was black as cola, I’ve left it in the bucket overnight, and now it’s clearer, like lemonade, and the solids have sunk to the bottom of the bucket. A sandy consistency.
