Overheating Whilst Towing

[Phill70]

Hi all

I have a P reg (97) 2.4 manual Previa.

She has started to overheat whist towing the caravan, but has been perfectly ok for the last 4 years.

She does not overheat during normal use.

The only change's I have made is to fit a new header tank, as the old one leaked quite a bit,

and a new thermostat.

Does not lose any fluid.

Any idea's

Glyn

[propnut]

Sounds like you have a flow issue. When towing you are obviously asking the engine to work harder which in turn generates more heat. As your radiator is a heat exchanger the coolant must flow through the radiator at a sufficient rate to allow for the exchange of heat from the coolant into the atmosphere. Three things could be at fault.

1. Blocked radiator core - buy a new one they are +-£70 from eBay

2. Viscous fan is not working properly - (if it is fine on the open road but overheats in town suspect this)

3. Water pump - unlikely as it is ok at other times.

My money would be on the radiator especially if you or previous owners have been using tap water to refill the system

You should be aware that these engines are known to blow head gaskets. Now you say you are not loosing any water but keep an eye on it as it it could be the beginning of the end of your gasket.

[Phill70]

Thanks

That confirms what I thought.

eBay time.

I had sort of ruled out the Viscous fan, and the water pump, as it is ok in normal use.

I will keep a careful watch on the fluid levels.

Question, you mention tap water.

Why should you not use tap water ?

Glyn

[propnut]

Take a look in your kettle for the answer ;)

[Phill70]

That explains that then :D

distilled water from now on then.

Thanks for the help

[JackD]

Probably not relevant here, but a cautionary tale.

My Previa was towing happily on a trip to the Alps, then started running hot and finally the temperature went sky high. There was no sign of any water loss and no clouds of smoke and steam to indicate a blown head gasket.

A French Toyota main dealer reckoned the water pump had failed, blowing the head gasket, and wanted a fortune to fix it and replace the radiator as well. On getting it recovered home, I changed the radiator, water pump and thermostat, but found I couldn't refill the system - no water was going into the engine. After checking everything I found the exit pipe from the radiator header tank was completely blocked with gunge.

This was probably the root cause of all the problems: the engine low on coolant but the blocked pipe fooling everyone (not just me!) into thinking there was plenty in there.

So, if you change a sediment-filled radiator, flush out the system, including the header tank and make sure all pipes from the header tank are clear.

Luckily in my case the head gasket hadn't gone and now, with effectively a new cooling system, everything seems OK in that department. Still other problems, but (touch wood!) not cooling ones.

JackD

[propnut]

That is a very good point and further illustrates the reason NOT to use TAP water. That is the source of the grunge. Distilled water in the correct 50/50 or better yet 60/40 antifreeze/water mix will never produce this sedimentation and the coolant system will run clear for many years.

The problem comes when, invariably, the system needs topping up and people use tap water.

Unfortunately in your case , and I am sorry to be a prophet of doom, it is just a matter of time before the head gasket does blow. With that level of sedimentation there is a 99.999% chance that the finer water channels in the head gasket are now completely blocked. This restricts the flow of water between the cylinders and valve chambers and redirects it to the larger, still open channels. This causes hot spots which eventually spell the death kneel to the head gasket. Hopefully this does not come to pass in the near future but do not be complacent, keep a beady eye on the old temp gauge.

[Phill70]

Little update.

New radiator, dual core one.

Filled using distilled water ;) and antifreeze.

She now runs a bit cooler,then she used to, one question though.

how long does it take for the thermostat to open ?

The lower hose from the radiator is cool to the touch even after a 20 mile run, whilst the upper one is hot.

[propnut]

That is correct, hot water enters the top of the radiator and then is cooled as it passes through the matrix resulting in cool water returning to the engine via the bottom hose for the cycle to begin again. If your gauge is sitting at around or just under 9.00 then all is good.