Hey all, Was driving tonight and apparently went beyond the RPM limit for the alternator belt I had. I heard the belt come off, and wasn't sure what happened. Gen light came on. When I looked at the water temp, it was hot. I don't remember the exact temp – my gauge maxes out at 250. I think it was somewhere between 240 and 250. I don't think it hit 250, but I couldn't say for sure. I pulled over as fast as I could – hard thing to do in a city... The engine dieseled when I shut the engine off. Luckily I had the old dayco top cog belt in the trunk. I have a couple questions: First: would reaching 250 engine temp cause any issues or engine damage? Head gasket? Warped heads? or would it survive without any damage? I replaced the belt with the dayco, and got home. The car appeared to run perfectly fine. I plan to change the oil before I drive it again. But I am concerned about the high temps. This is a low mile engine, only 7 thousand miles on it. Oil pressure was good when I was driving home as well. Second: From what I read, a lot of the modern belts tend to pop off. I had an old dayco top cog 15455 in the trunk. Is this the belt I should be using? I just don't want to repeat this fiasco. Many thanks in advance for all the guidance, –Ryan
These engines are very tough. A momentary spike to 240 or 250, isn't going to hurt it in my experience.
Running an engine to "overheat" can result in several critical areas of "failure/damage. First thing to suffer is the rings (temper/tension). Second is bearings, from detonation. Third is gaskets, due to excessive pressures. Fourth is warping, cracking of heads. (three and four may often be associated events) Fifth is piston "swelling" resulting in ring land cracks/failure and scoring or momentary "seizure" and damage to cylinder walls. Sixth, is valve damage depending on how long run hot (exhaust valves), and hanging/stuck valves that damage guides or worse, "interference" with valves/pistons, with hanging/stuck valves. Depends on load over time. If it was a short transition, and the engine was not under load, you may be OK. Run a compression and leak down test. Drain oil and examine for metal, as well as cutting and inspecting the filter. Pull plugs and examine for any signs of detonation (may look like very small metallic "splatter" on the plug, insulator tip, strap electrodes. Look for any signs of blown gaskets, "plugs being "real clean" (indicating coolant "cleaning" of plug) or coolant/oil around head/gasket. Test for exhaust/combustion gasses in the cooling system. Many times, a short excursion into 250-ish (Fahrenheit) range will not result in damage. But keep an eye on things. If you hurt the motor, it will let you know, you just need to "listen" to it telling you. If you find anything that is not happy, stop and evaluate the proper fix. Better to spend a few hundred to thousands of dollars, than push it to the point you spend double or quadruple that amount. (and, yes, I realize it is easy for me to spend your time and money, from this side of the computer monitor...) As a real life example, I had a radiator mount fail, the radiator moved back at the bottom and the fan blade cut the radiator. I drove a few miles and saw the temp increase, the "idiot" light came on about 1/mile from my house, the gauge was pegged above 250F, and the engine started "knocking" if I gave it any throttle. I drove it as gently as I could, and kept RPMs at the spot where it minimized detonation, and kept the least load on the engine. As I got near my house, I pushed into neutral, rolled up into my yard, popped the hood, grabbed the hose and started working on spraying water on the front of the radiator in an attempt to cool down the engine. The car stalled after about one minute, so I stopped (shut off the key) and let the car sit for a few hours. When I came back, the exhaust side of the engine was very dark "burnt brown color to the paint". I started the car, and it fired right up, I added water to the radiator and once it was filled, I got the car to operating temps, drove it around and it "acted fine. Did all the "steps" I mentioned above, found nothing out of place, so I just started driving again, and nearly 10 years and many thousands of miles and multiple state runs, it continues to run good and hard highway speeds of 80-85 for hours/hundreds of miles at a time. (it's a nailhead) On my '68, Skylark (350 with a 4bbl) I picked it up 150 miles 2.5 hours away off a transport truck, and proceeded to drive it home. Was fine at 80 MPH for about 45 minutes, then I started noticing it was lightly pinging on the "up hill", so I pulled off at a gas station, and realized it was "hot" so I played the hose on the radiator until it was cooled down a bit, then shut it off and realized the "temp switch" wire was pulled off and taped off from the temp switch. Hooked it back up and started driving again. The light came on about 15 minutes (more up and down elevation) so I pulled off to "hose it down again". Since I was less than an hour away from home, I drove until it started getting hot and just before the "hot" light came on, I pulled over and cooled down the radiator. Got it home. Next morning, I did a "power time" and found it was very retarded and the vacuum advance was not working. Replaced the vacuum canister and with corrected timing, the "overheat was gone". Drove the car on and off for about 6 months while I built the 430 to go in it. It never ran hot again, and ran very well. So, all of this to say, if you hurt it, you should be able to determine that. If you did not hurt it, drive it!
Hard to say if any damage without a tear down, BUT, If it runs/idles fine and oil pressure is the same I’d drive it! If it wasn’t rattling then it was just a temp spike, not long enough at “Overheat” to cause damage. But if the temp spiked to 250 and held there without shut down, then the metal parts have time to get “HOT” and cause damage.
Get rid of the 250 degree temp gauge . A normal engine will not boil the coolant till it reaches appx. 260 degrees . A 15 lb pressure cap helps raise the boiling point fro 212 to 260 . Besides that gauge is probably out of wack from the shock of the high temp . doesn't matter if its an electrical or Mechanical gauge
Thanks for the replies. Both the best case, and worse case scenarios. I will change the oil and inspect further when I have the time. I don’t think I drove it long enough to have significant damage. Between the alternator light coming on and powering off, it was no more than a couple blocks. That being said, it did get hot enough to diesel after shutting it down. It ran perfectly fine on the way home. No coolant/oil cross contamination. I didn’t check the plugs yet. Or do any diagnostics. I’ll order some new top cog belts and put them on as well.
Your very likely fine with just a short high temp condition like that. I don’t even know that I would change the oil, especially if it’s synthetic. what causes problems like cracks heads and blocks is after a over heat condition when you loose coolant due to a busted hose or leak. If you then add coolant too soon without letting the motor cool down enough and especially if you fill & start, that temperature shock will likely crack something or in the least fail a head gasket if that was not part of the coolant loss in the first place.
If you pulled it over quickly as you said, you'll be fine. I did the same thing at the track. Saw it in the shutdown area, pulled it onto the return road and shut it down. Got a tow back to the pits, put another belt on, and it was fine.
That’s helpful. Thank you. That makes sense - the temperature shock causing cracks. I had a Volvo that had a severely warped head when the exhaust side overheated - but that was an aluminum head. Common problem, same thing just happened to a friends Volvo. But these are iron heads - so should be more robust. I’d hope. I’ll change the oil anyway, because it’s about due for a change. sounds about the same. I’m happy to hear your whip is still intact. Like I said, biggest concern was the dieseling. thanks for the input everyone
Check your pulley alignment. I've never thrown a belt yet, top cog or standard style, shifting at just under 7k.
Me neither, come to think of it, years ago I had an alignment issue due to the wrong water pump, NEVER noticed it till years later, belt didn’t care. If you think of the Corvair belt arrangement, I’m surprised it even went on, let alone stayed on!
