Water pump...replace?

1994 F150, 164k mi. 4.9L I-6.

I’m in the middle of a head gasket job. While wait for the machine shop, I figured it’d be worth inspecting the water pump while it’s accessible.

But what constitutes a “bad” water pump? Impeller erosion, obviously, but what else? Bearing play?

Thsnks for input…including whether I should replace, inspect, or fuggetaboudit!

If the pump has never been replaced then I would do it if the truck were mine. The seals would be 20 years old and prone to failure at any time. My opinion is to be a bit pro-active with some things.
A new thermostat is a must with every head gasket job.

The three big water pump killers. 1) seal leak, 2) bearing play/noise, and 3) impeller erosion. Also, like @ok4450 said, if this is the original pump, or it is more than 7 years old, I’d replace it just because. It could save you the hassle of replacing it later due to reasons 1 or 2.

Thanks…I’ll replace it. I bought it with 124k on it, and I don’t know the history.

I’ll pass on the thermostat right now, because it didn’t overheat, the coolant temp is observed behaving normally, I’ll be driving it/monitoring it, and the thermostat is easily accessible even after full assembly.

One question, though: is it advisable (or even possible) to run “old-school” coolant? I read somewhere that OAT coolant really isn’t for cars with non-pressurized overflows, because it doesn’t play well with even traces of dissolved oxygen in the coolant system.

Personally, I run old school green in every car our entire family has simply because it’s always been problem free.

One of my son’s car uses Dex-Cool and that car went through 3 water pumps in the first roughly 80k miles. It kept sludging up through repeated flushes and there were zero leaks and loss of coolant. After the 3rd pump I flushed it again, filled it with green, and it’s never had an issue with leaks, pump failures or sludging since and up to the current mileage of around 250k.

While you’re in there, might as well do the timing chain.

It’s probably stretched.


You’ve got the cooling system empty, the thermostat and housing are off, you’re proactively replacing the water pump, a new t-stat gasket will come with the head gasket set, you don’t know the service history of the car, why wouldn’t you replace the thermostat?

That truck originally came with old-school green coolant, that’s what I’d put in it.

Why does it need a head gasket?

No chain, just bakelite gears. It’s not an interference engine, so I’ll probably wait for issues, then upgrade to metal at that time.

I thought even “green stuff” was partially organic these days, unless you sought out “original formula” coolant.

I think the gasket was partially breached when I bought it and got worse. Ran fine, but a sound at WOT between knock and "pfft."
Gradually got worse until it happened at half throttle or more…a precautionary compression test showed 150-170 on all cylinders except 95 on #3. Looked to be leaking toward the head bolt outward on the “non-intake/exhaust” side of the block.