i have a 92 4ZD1 truck. the head has been replaced in the recent past. 178k miles. since i got it, it has been losing coolant. i have to add a quart or so after a 20 mile trip. i recently flushed the cooling system out and the old stuff was brownish in color and looked like the original coolant. no signs of external leaks that i can find. when i shut it down, i can hear a bubbling or gurgling sound for a second or so. anybody got any ideas?

Not sure how long ago you flushed the coolant, but if there is truly no coolant leaking externally, then I can think of 3 potential problems:
1)When you replaced the coolant after flushing, you trapped air in your system and you are slowly "burping" the system and as a result, you end up being able to replace the burped air with additional coolant (the gurgling you referred to implies air in your cooling system
2) Your coolant is ending up in your crankcase (check the oil dipstick for milky engine oil
3) Your coolant is leaking via the heater core and ending up under the floormats in the cab of the truck (you would smell coolant in the cab if this was the case)




you truly can't find any leaking

thanks for the ideas. i appreciate it.

air bubbles are a possibility for the noise. not sure how to get them out. they cannot be responsible for the quart a day i have to put in the radiator.

i have to add a quart a week to this oil burning engine. the oil is nice and clear.

i already checked the heater core for leaks. no dice.

anybody else got any ideas?

I'm voting for either cracked head or blown head gasket... most likely between #2 and #3 cylinders for either. If you're losing that much coolant, its not leaking externally, and there is not a lake in the floorboard of your truck; you're pretty much left with an internal leak of some kind. The bubbles upon shut down can be a sign of this as well. Time to run a compression test.

Agreed. You say that the head has been replaced in the recent past, was it replaced with a new head, or a junkyard piece? If it was junkyard, there's a chance that the 'new' head is warped as well, unless it was carefully checked. Even if the head is solid, if the head gasket was damaged during install, or mis-installed, you could be experiencing a leak as well.

Out of curiosity, do you know how much coolant you put back in when you originally flushed it? That would at least give you a ballpark as to how much potential air in the system you would have to burp out.

James

These guys are right, and I'll throw in another vote for cracked head.

But...take a close look under the exhaust manifold. You might have to move the skirt in the driver's side wheel well to get there. What does the side of the block look like? Stained? Streaked? Just because it is not puddling, does not mean you don't have an external leak. These engines will also blow out the head gasket from the cooling jacket out on that side of the engine.

Good Luck,
Michael

That's a lot of coolant to lose with no visible leak. You'd be trailing a plume of steam and I wouldn't think it would run so well with coolant getting sucked into the cylinder. Any green dripping out the tailpipe? There were a couple of lines on the underside of the intake manifold that circulate coolant in the throat of the throttle body to warm up the intake air on the 4ZE engine. Maybe the 4ZD is similar? Coolant also circulated in the intake manifold.
Maybe pull the wheel and drop the mud flap to get a better look at the passenger side of the engine. Gurgling is just air redistributing. You don't want to run your vehicle with air trapped in the head 'cause that restricts the coolant from really circulating which will eventually melt the valve seats out of the head... ask me how I know...

its been getting parked on a patch of snow lately. no signs of leaks that i can see. are there coolant passages between the intake manifold and the head on this engine?

you havent said if youve checked your oil yet. if you are losing a quart/20 miles and cant find any external leaks (they would be obvious) its in the crank case or the combustion chamber. if it is in the cylinders it could be coming from a cracked/warped head, head gasket, intake manifold.

this might be tricky! if its in the cylinders it wouldnt leave a trace, it would leave as steam in the exhaust. but if it is losing a quart every 20 miles that would be roughly equivalent to running 25% water in your gas tank! i think it would run terrible.

I'm not sure on the 4ZD. There are coolant passages in the intake manifold on the 4ZE cause that's where the temp sensor for the ECM is screwed in. I think part of the reason for the coolant circulation is to temper the air to keep the NOx down. And like I said there are also two coolant tubes on the underside of the throttle body which appear to prevent frost build-up in the throat under certain atmospheric conditions (like freezing fog). Happened to me once with a VW. Strangest thing to pull the air filter and see a plug of rime ice in your carb.