Who can figure this one out?

[Tleg93]

I have a friend (no, it's not me) who has an L with a stubborn overheating problem that no mechanic has been able to trouble shoot as of yet.

Here's what's been done so far:
He replaced the radiator with a new one.
He replaced the water pump.
He put in all new hoses.
He got a new radiator cap.
He replaced the thermostat.

Some symptoms and info
At one point he found metal in the oil and it turned out to be from the water pump apparently.
It does fine on idle, overheats on the highway.

It's odd that it overheats on the highway because I'd think that the air would keep it cool. Usually you'll get overheating when you stop. They've basically replaced his entire cooling system except the fan.

[tris91ricer]

..and the fans are coming on, right? Otherwise, I'd look at maybe the fans being the culprit...?

[Legacy777]

Metal in the oil? The water pump doesn't come in contact with the oil....?

Is it an OEM thermostat?

Has the system been properly bled of air?

If everything else is fine, I'd lean towards head gaskets.

[vrg3]

Is it plausible that cooling passages (either in the water manifold or in the motor itself) are clogged? Has the system been power flushed or anything?

Did they check the coolant for exhaust gas? It could potentially be something like a leaking head gasket, right?

Is the water pump lubricated by motor oil? I thought its bearing was sealed.

[Tleg93]

Metal in the oil? The water pump doesn't come in contact with the oil....?

My bad, isn't wasn't metal in the oil. They found metal when they drained the coolant. He was told the heads were in good shape. No frothy oil and no noticeable leaks.

[Legacy777]

Unless they do a test for hydrocarbons in the coolant and it comes back negative, I wouldn't rule out the head gaskets. Other possibility is a crack in the head or block.

[Tleg93]

Is it plausible that cooling passages (either in the water manifold or in the motor itself) are clogged? Has the system been power flushed or anything?

Did they check the coolant for exhaust gas? It could potentially be something like a leaking head gasket, right?

Is the water pump lubricated by motor oil? I thought its bearing was sealed.

I guess they pumped coolant through the system and tested for leaks.

[vrg3]

Hmm... If chunks of water pump got into the coolant, it does seem plausible that some could still be in the system somewhere... And if they block flow enough, couldn't that cause the water pump to cavitate at higher speeds?

[J-MoNeY]

It's the headgaskets. The coolant will not be milky always. Replace those and I'd bet you the problem goes away.

[dzx]

I'd check the spark plugs for the hell of it. My mom's car overheated several times in omaha and we found out it was just a loose spark plug, might have been all the way out, i cant remember as it was years ago.