Sudden overheat - then back to normal

[boma23]

Hi

had a funny turn last night in the truck. Whilst we all know the fairly well documented issues with the stupid autobox cooler design, which can cause overheating on long, drawn out uphills in very hot weather (not often in the UK), it appears last night my truck had a more serious turn.

With a full load of passengers and tools, going up a very steep local hill, the temperature suddenly shot up and I caught it on the edge of the red. It overheated very quickly, and much more suddenly than when pushed over edge normally (i usually see it start climbing much more slowly.

Now this is the weird part - normally if temps ever gets up there, I would simply stop, letting the engine idle with the heaters on full and let the fan bring the temps down, which would usually happen pretty quickly.

This time though, there was no heat coming from the heaters, and even at idle with the fans on, it seemed the temps still wanted to creep up (sitting in the red ). I also noticed a slight bulging on the top radiator hoses. This says to me that maybe coolant wasn't flowing properly??

I left it off to cool for 20 mins instead, and once back down to normal temps again, started the engine, and it ran fine again, heaters back on and working again, and taking it steady it didn't overheat again...


Thinking about this, my worry / thoughts were that:

1. Waterpump seizing then freeing up again?
2. Potential blockage floating around the cooling system? (Maybe damaged water pump vanes?)

Any other thoughts would be welcome, as I'm tempted to order a new Water pump on the off chance.

Car has 119,000 kms, and had full coolant change/flush and new lower temp thermostat a few months back.

[boma23]

just to be clear, my post sounds like the truck has an overheating problem. It genuinely doesn't, usually only very certain conditions will cause the overheating. I live in 35 deg heat and near 100% humidity sometimes, so on a midday climb in beating sunshine, up a 1/2 mile 1600ft climb where I don't use the auto gearbox TC lock to prevent auto heat build up, and put my foot down causing the box to generate lots of heat, the system is simply overloaded by design (well documented on aussie forums).

Normally, and if using the TC lock on hills, the temp stays solidly bang in the middle.

[TonyN]

If the water pump siezed the belt would have screeched like a banshee, you'd soon know.

You don't mention checking the coolant level, how was/is it?

[boma23]

my bad - feel a bit stupid now.... I checked the reservoir last night and it was low, but still with liquid in, so topped up a bit.

Today I've just gone and took the rad cap off, and between the rad and reservoir it took another half a gallon, so yes it was low.

Oil looks ok so hoping it's maybe dropped over time rather than suddenly disappeared, but even though this truck does work very hard (everyday is hills and heat), would you say that using half a gallon since last top up about 1000 miles back is bad?

hoses aren't showing leaks, but will need to investigate properly i suppose. traditionally it hasn't really used a lot of coolant so am a little worried now.... i checked the exhaust last night whilst it was overheated, and revved it but there was no moisture or steam coming out.