Greetings All,

Please raise your right hand and repeat after me: "I will not let anybody borrow my truck". With that tough lesson behind us, I could use some help determining what damage, if any, was done to my truck after it lost all coolant and overheated.

The scenario: My son was borrowing my '84 F250 (351W, 205k miles) to move. How could I say no? Said young man has a poor sense of smell, which is important. He was driving down the freeway at night when my add-on heater bypass valve broke. A fitting on the valve failed and all coolant dumped overboard, probably within seconds. It was dark and had been raining, so the coolant leak wasn't obvious and he didn't notice the smell. At some point the engine started running roughly and losing power. He pulled over as quickly as possible and called me.

By the time I arrived, the truck had been sitting for about 30 minutes. For having lost all coolant (which neither of us realized at the time), everything under the hood was remarkably dry. I noticed a small dribble on the ground but it was near the AC evaporator drain so didn't think much of it. Nothing else under the hood seemed amiss.

Initially the truck wouldn't start, but it did crank over. I noticed the fuel tank in use was nearly empty. I switched tanks and coincidentally the engine roared to life. Believe me, I wasn't doing any in-depth troubleshooting on a narrow shoulder on a busy freeway at night. I was only running through some quick items to see if it could be moved to a safer place.

Once the truck started, I thought we were good to go. Although it idled and revved up just fine, once I started moving I knew something was wrong. The engine knocked like crazy (preignition?) and was very low on power. I got up to maybe 40MPH, noticed the temp gauge climbing rapidly, and pulled back onto the shoulder. (The oil pressure was fine the whole time.) It was time to call a tow truck. 24 years I've owned this truck and it's the first time it didn't come home under its own power.

The next morning it was easy enough to determine what happened. I replaced the heater bypass valve (different style, hopefully won't fail again) and refilled the coolant. The engine fired right up again and ran perfectly. I ran a pressure test on the cooling system and it held steady, hopefully meaning I didn't warp a head or blow a head gasket. I also used a combustion leak detector at the radiator neck and it passed with flying colors. I took the truck for a test drive up to 70MPH and it ran fine as frog hair.

So did I dodge a bullet on this one? The truck drove at two short intervals without any coolant. My son didn't notice the coolant dump so has no idea how long he was driving like that, but he said he pulled over within a minute of the rough running. My little attempt was about 2 minutes max, probably less. The temp gauge (sender no longer immersed, so probably not of any use) reached 3/4 max.

When an engine runs without coolant like that, where is the damage most likely to occur? Scuffed pistons and scored cylinder walls? Warped valves? Warped/cracked head? Blown head gasket?

Has anybody here had an engine ruined by overheating due to coolant loss? Did the engine fail right away or was it days/weeks/months later? What actually failed, so I know where to look? Fingers crossed that I'm okay, but would like to hear the voice of experience.

Thanks

 

My old 302 over heated due to a bypass hose , drove it 30 miles to get home with hardly any coolant . Next day fixed the hose . I drove that truck for 2 years after that, sold it to a buddy that still uses it for a lot truck . Just be glad you have iron block and heads , just watch for coolant in the oil . I also had a mark viii that over heated due to air in the system an with that aluminum head and block it blew the gasket an warped the head . Id count your blessings . Worst comes to worse an a head is bad or gasket ,it's just a excuse to do some up grades!

 

In my opinion, yes, you dodged a bullet....to a point.

Those engines are pretty tough, but problems may not arise for miles or years to come. If you hear no out-of-the-ordinary noises, it runs smooth, and everything "seems" fine, I'd change the oil and run it. As long as you had oil pressure the whole time, the bearings, pistons, rings MAY have been saved. Keep your eye on it though. Watch for coolant usage, oil consumption, etc..

At the first sign of any problems, I'd pull it apart for a rebuild.

I've heard a lot of stories like that through the years (actually worse than your scenario) and the engines still lived a long life. But, don't use that as a reference to how yours is going to be.

 

I think you got truly lucky. I would baby that engine from here on out. Not knowing how long it ran "hot" without coolant is scary. Expansion and contraction in an engine is subjective. I personally would flush the coolant, as well as engine oil/filter over the next 500 miles, while keeping an eye out for leaks. Replace the thermostat as the high op temp may have cooked it (overheated the spring, reducing it's tension).

 

Thanks. I forgot to mention I found no evidence of coolant in the oil. I will change the oil this weekend. (Won't need to drive it until then.)

I drove it to work today. (52 mile round trip) Zero problems, as if nothing happened. The only issue was me panicking in reaction to every slight shudder, rattle, or noise the truck made. Might take me a while to relax and know the truck will be okay.

So does anybody know how such an overheating event actually affects an engine? What type of failure might I see in the future? Just a slow decrease in performance, caused by an increased rate of wear and tear? Or a catastrophic thrown rod or similar outcome?

The truck is my backup vehicle, getting maybe 5k miles per year. At such a rate of usage, it's tough to rationalize the expense of a rebuild if the engine could still function reliably for years like this. That's why I'm really curious how any hidden damage might manifest itself.

Above all, I want the truck to stay reliable. I'd be okay with a slow decline that would still get me home every time. That's basically what I already had, so a minor increase in the rate of decay would be acceptable, considering the low usage rate. On the other hand, if a now-likely failure mode involved pistons liberating themselves through the hood, then a preemptive rebuild is in order.

Discuss amongst yourselves...

 

I had better luck by liting hot engine cool by slowly. I left a tractor running an pto pump. I come back about 30 min later rad hose busted leaked all coolant out. The motor had stop running and got so hot it burnt the paint on the block. We replace the hose filled the coolant and been using it every day for 5 years.

 

Oy very! That's really hot if the paint burned. That gives me more hope my truck will be fine.

I've pretty much hit a dead end trying to learn what actually gets damaged when an engine overheats. I've found plenty of info online about warping on other engines with aluminium heads, but not much else. I guess I'll put that quest on the back burner for now.

I can, however, rephrase my question slightly and convince myself I'm not beating a dead horse. So how about this instead? When an engine overheats and stalls, what actually stops the engine? A couple of theories careening around inside my cranium:

1) Hot spots inside the engine cause preignition, which progressively gets worse and reduces power drastically.

2) The aluminium pistons expand faster than the cast iron cylinder walls, tightening the gap and creating lots of extra drag.

A combination of the two? Any other ideas? Just doing my usual, tilting at windmills and trying to understand stuff that really doesn't matter.

 

I know that feeling, and it sucks.


In my mind, I would think the pre-ignition would happen waaay before a total lock-up. That would be enough to lose power like you said it did. If the engine locked up, I doubt it would run as good as it is now.

The only thing I think I would be concerned with is possibly a broken ring or two. You could do a bleed down test and see if there is any ring damage. A broken ring would probably show excess oil consumption too.


A little story about a buddy of mine:
Him and another guy took his 3/4 ton van with car trailer to Georgia to pick up a car. (The van was a '93 fuelie 351). On the way back, his buddy was driving (at night) while he got some sleep in the passenger seat. He woke up a bit later and yelled "You're in second gear!!" Not two seconds after he yelled that, the engine shut off. They got out, lifted what hood a van has and saw a bright red glow from the exhaust manifolds.

What happened was said driver was in second gear on the freeway, running the rev limiter, which leans the engine out. They got a tow all the way back up here (Luckily we have a buddy that owns a towing company). Got van back and pulled engine. Still locked up TIGHT! Couldn't budge a single piston. He scrapped the entire thing and put a Ford reman in and was done with it.

When the engine got pulled, you could see just how hot everything got. I really doubt yours got anywhere near that temp with the way it runs, and no noises. Run it, but keep an eye on it too, at least for now until you know it'll be fine.

 

A little follow-up:

After six years, the motor finally gave up the ghost. I had very low compression (30 psi) on two adjacent cylinders. Most likely a blown head gasket, but the oil consumption and blow-by had increased dramatically at the same time. I pulled the trigger and went with a reman engine. I don't believe this recent issue was caused by the overheating incident so long ago. The engine gave excellent service all that time since then.