Effect of overheating on big end bearings

[speedtwelve]

Hi folks

Head gasket's gone on my Rev 2 turbo. The car began to overheat, didn't have anywhere safe to stop the car, and ended up running it with the temp needle at the top of the gauge for a couple of minutes. ECU light lit on the dash about 30 secs before I could stop the car and shut the engine off. Kept the fans running, coolant and steam pouring out of the overflow pipe from the expansion tank.

Left it for ages to cool down properly, topped-up the coolant and drove away. Engine has started and runs fine through the rev range, revving freely (on short test journey).

There are no signs of overheat-damaged big end bearings. No knocks, rattles, the oil light goes out quickly from cold just as before. Any chance there is some bottom-end damage that might appear later?

Confirmed the HG failure: bubbling in the coolant, sniff-tested it and it tested positive for CO. No steam in exhaust though, and no mayo in oil.

Any opinions?

[Ian Geary]

I'd have thought big end bearings would be more likely to suffer from oil pressure loss, low oil level or old/dirty/unsuitable oil than coolant problems.

OK the oil (and turbo) are cooled by water, but it sounds like you did the right thing and this wasn't an issue.

Assumming the lubrication system is OK, you engine should be alright (once HG fixed). As you've suggested, knocking from the bottom end on acceleration would be a symptom, and you don't have it.

So, what caused the HG to go? Has it lead to warpage of the head? Do you think there was a fault in the cooling system that set it off?

hth

Ian

[speedtwelve]

Thanks for the reply Ian.

I'd heard that prolonged engine overheating can cause big end bearing failure, I would guess due to the shells softening?? Pistons seizing in the bores is the worst case scenario, but managed to avoid that!

The rest of the cooling system on the car is good. The car was originally owned by a friend of mine, but when he bought it 2 years ago I helped him when he was viewing. The car was mechanically sound, the only reservation I had was that the coolant at the time was not so much Toyota ForLife, more like water! Although it has been run on the correct stuff for the last 14000 miles I suspect that perhaps alloy corrosion in the head has caught up with it. I'll get it pressure tested and machined when it's off, and stick a metal gasket in.

Cheers

[welly_59]

i really doubt you could get bigend failure from overheating. no water is in contact with them so unless you super-heated your oil(i mean like so hot it caught fire) then it aint going to happen.

[70by]

your pistons would sieze in the bores long before there was any heat damage to the big ends,multigrade oils have come along way,i've seen engines off 140c with no damage to big ends or main bearings

[speedtwelve]

Thanks for the replies.

Remember seeing a vid of a Mk1 that was deliberately run at the rev limiter with no coolant in it. It lasted something like 5 or 6 minutes before it let go (quite spectacularly).

[jonb-]

Thanks for the replies.

Remember seeing a vid of a Mk1 that was deliberately run at the rev limiter with no coolant in it. It lasted something like 5 or 6 minutes before it let go (quite spectacularly).

I'm not sure that mk1 had any oil in either

[welly_59]

yep no oil or coolant and it was one of the pistons coming through the block that finished it!