Sequence of failure when coolant overheats?

[PackardV8]

I was asked to give a second opinion on an overheated engine.

A local rebuilder Ford mod motor had valvetrain noise from the get-go. While the owner was trying to troubleshoot, the cooling fan was inadvertently disconnected before a road test. He pulled into stop-and-go traffic, within a few blocks and minutes, noticed the coolant temp gauge rising, got out of traffic within another 3-5 minutes of low RPM driving. Radiator cap was venting and temp was gestimated at 240-250. He plugged in the cooling fan and coolant gauge temp started to drop immediately. He was back home in another 3-5 minutes without ever having exceeded 2,000 RPMs and temp was back to normal.

The valvetrain noise turned out to be part of a batch of bad cams the rebuilder received from a here-to-fore reputable cam company on the northwest coast. They're reportedly having difficulties with mod motor cams.

However, since the heat tabs on the block show overheating, the rebuilder is trying to dodge the cam warranty claim. I did a compression test and it was to spec, pulled down the engine and there is no sign of piston scuffing, no valve sticking, heads aren't warped.

Bottom line, since this overheating was brief, no load, oil clean and clear, what are the most likely failure areas and what would you expect to see?

[peejay]

Some cars don't even turn the fans on until 245 degrees depending on the operating conditions.

[mag2555]

If any ware at all took place with those temps and the brief time it was a bit hot I would have to say that ware would show up in then areas of high heat slow oil flow change . To me that area would be in the exh valve guide and exh rockers!

[Rizzle]

My guess would probably be worse than yours, but I'd expect to see skirt scuffing at the very least to indicate overheating, since the extra temp would make the piston expand more vs the bore. However that would require both to be overheated at the same rate they typically do, and since this was not a WOT situation, there is probably enough clearance factored into a warm block/WOT piston temp to cover your situation as well.
There was mention a while back that the high operating temp of the dodge 4.7's (iirc ~240-250*F) was mentioned was causing the valve seats to drop out.

If its got the valvetrain symptoms of a bad cam, had it before the overheating situation, and the company knows about the batch of bad cams, I see no good reason why they would expect to get out of warrantying the cams/any issues caused by the defective cams?

[Truckedup]

The engine rebuilder gets the green light.The engine temperature was activated and If the warranty states not responsible when overheated t...The loose wire was the fault of the installer, the driver should have more alert to the temp rise on a fresh engine....

[BCjohnny]

In today's world the heat tabs are the key. The rest is just moot............. JMO.

[PackardV8]

Thanks for the replies.

Agree, the warranty is clearly voided when overheating is proven.

In this case, my initial inspection doesn't show any damage and so far, it's as good as when he got it. I'm just asking if there's anything else I should be checking.

What's probably going to happen is when the dust settles, he may get two new cams and pay for labor in, apart, gaskets, back together and back in.

[4banger]

Seems to be two different issues here.......the valve trainissue and the over heating issue. As for the overheating issue, I think the emgine builder is safe b/c the heat tab is there for his protection from someone else's mistake. With the valve train issue, it seems that it was verified before the overheating so the cam company should have to make good on the warranty.
If you didn't find any noticable damage on tear down I would agree with you on the new gaskets, cam etc.

[numboltz]

A bit tangential perhaps, but what about cylinder deactivation software, for overheating protection? How many mfrs are using it now, or is anyone? Never actually encountered the situation so I`ve only read about it, but it is supposed to work in a situation like this.

[Fordracer347]

A bit tangential perhaps, but what about cylinder deactivation software, for overheating protection? How many mfrs are using it now, or is anyone? Never actually encountered the situation so I`ve only read about it, but it is supposed to work in a situation like this.

I know ford is using it on some of their hybrid stuff

[Kevin Johnson]

A bit tangential perhaps, but what about cylinder deactivation software, for overheating protection? How many mfrs are using it now, or is anyone? Never actually encountered the situation so I`ve only read about it, but it is supposed to work in a situation like this.

Additionally, there was the Cadillac Northstar engine series, which featured a "limp home" fail-safe mode. If the engine lost coolant, the engine controller could cause the engine to run on half of the cylinders, alternating between banks. This would air-cool the engine, allowing it to drive up to 100 miles without coolant.

[racinnut15xm]

You already have it apart they wont send the cam to you under warranty and let the customer handle the rest?

[Olefud]

There are another two questions here; legal and technical. The warranty language and temp deal with the first.
But technically, with a 15 psi radiator cap the temp would go to 245° F and stay there until the water boiled off. I’ve finished a number of races under this condition so thermal damage is possible but not likely under such usage. That’s the purpose of the cap, increase temp for heat rejection but let the engine live.

[MadBill]

For the overheating to have damaged the cam, the oil would first have to break down. If analysis showed the oxidation level, etc. to be within accepted parameters, it could logically be concluded that overheat played no part in the cam issue.