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93 Pathfinder overheats, doesn't maintain water level

Have a 1993 Nissan Pathfinder that began overheating a few weeks ago. It’s bee relatively stable in terms of maintaining a consistent level of coolant up until this past week. Now it seems like I have to fill it up each day!



Some things to keep in mind:



I HAVE NOT added any coolant, only water. I imagine that this is going to be an issue since the boiling point is lower than what it would be with antifreeze.



The heater doesn’t always blow hot air when the radiator is full.



The heater does blow hot air when the temp gauge is around normal.



The heater seems to get weaker as the engine heats up more…not totally sure why.



My tachometer bounces (which it has been doing for a while) and I read that this may be related to an EGR valve. Could this be related to an overall vacuum issue (tach & overheating)?



Other than that, I haven’t put any major repairs into the vehicle for several years - 6 to be exact. Just oil, filters, and fuel (and tires)…



Please help!

Oh also, it’s not leaking any fluid or anything (visibly at least). Forgot to mention that.

Well, that coolant has to be going somewhere. It’s either leaking out or being burned up; no visible leaks lends itself to being burned, and consumption at this rate could potentially indicate a blown head gasket. That said, it could also be nothing more than a weak radiator cap that isn’t holding pressure, allowing the coolant to simply boil away. This would be exacerbated with just water, since it boils much easier than a coolant/water mix.

Have you checked the condition of your engine oil? If it appears at all like a milkshake, that’s a dead giveaway for a blown head gasket. You’d also see bubbles in the radiator if this is the case, and potentially see white smoke out of the exhaust.

However, I’d suggest starting with the cheap, simple stuff first. Buy a new radiator cap, top off with a 50/50 mix of coolant and water, and see how it behaves. Post back if the problems continue.

Thanks for the insights! Haven’t noticed anything unusual about the oil or exhaust, but I’ll give it a good look today while I’m under there. Seems like the exhaust has always been a little “steamy” (if that makes sense) in cold weather (the truck is from Fargo, now living in Texas). Exhaust is totally clear in warm weather - no smoke at all.

I noticed yesterday after driving that once the truck got to a high temp, there was a hissing sound which was not coming from the radiator cap. I won’t rule it out completely, but it seems like something is leaking when the fluid gets heated/radiator gets pressurized. The coolant overflow tank is empty as well…

The mystery continues.

I checked it out and am now pretty worried about the situation.

I filled it with coolant while the engine was cold.

While filling it, I noticed that it took almost a full gallon - then there seemed to be a trickle from what appeared to be the area above the thermostat, but not the actual thermostat itself.

It seemed to be coming from the top of the engine block…which doesn’t really make sense to me (isn’t head gasket rear/bottom?).

??

The headgasket is at the top of the engine bloc. It seperates the block from the head and seals the cylinders and the oil passages. The top of the water jacket is also sealed by the headgasket. A breech in the gasket could cause all of your symptoms.

I’d suggest a pressure leakdown test…with the coolant full. That’s a test where the cylinders are pumped up with air and checked to see if they hold it in. That’ll tell you (A) if the headgasket is breeched, and (B) if the cylinder is pushing coolant out the side of the gasket through the breech.