Previa Overheating Uk 2.4i Petrol Manual Model 1994.

[GLEN1]

Please help me Toyota people.Recently changed coolant in my Previa ,best car I have ever owned.It now appears to start over heating when stationary in traffic conditions ;cools with speed or when heater put to the max.It was fine before I touched it temp gauge never went above half even when stationary in Italian sunshine.What have I done ? Followed guidance in service manual to ensure no air in system this appears to be something else .Any ideas gratefully received .I am half cleverish with mechanics ( unfortunately mostly motorcycles ).Is this typical of fan clutch / thermostat etc .Seems odd that it was ok before I touched it .Coolant drained clear bit brown but no sludge to give head gasket concerns and at speed engine remains cool regardless of heater setting in car. :( Car has done 142000 Miles touble free self serviced by myself (first time I touched the coolant though ,)changed fan/ alternator belt at same time but this is also tight and correct in operation.

Cheers B)

[propnut]

If you are 100% sure that there are no air blocks and have correlated this fact by checking your heater is blowing hot then I suggest you check the viscous fan. By virtue of the fact that it cools when in motion but overheats at Idle it certainly sounds like this.

A viscous fan is filled with a silicon based gel that is fluid when cool but hardens when hot. At idle the air flow through the radiator is reduced and the little air that passes through the radiator starts to get very hot. This in turn solidifies the gel and locks the fan into operation whereby it increases the air flow hence cooling the coolant.

With the car off tie a piece of fairly strong cotton to one of the blades and the other end to something immovable in the car. Start the car and if once it gets to operating temp the cotton has still not broken then your fan is finished.

Next thing is your assumption that because it ran clean the system is clear . BIG MISTAKE.

These things gum up big time at the top of the rad and no amount of flushing will clear it. Either strip your rad (and yes this is possible) or buy a new one for +-£70 from eBay. The fact that it was fine before you changed the coolant may just be coincidental or that you may have upset some lump of gunge that hadn't moved before.

You could well have a weakened rad cap, change this and see if it helps. The system needs to retain pressure to cool efficiently.

Fianally, at your mileage you are pretty much going on for the blown head gasket route. If during your draining/refill/bleeding process you allowed a hot spot to develop at a section of head that was about to go then chances are it has now done this. If you are losing coolant I suggest you suspect this

[GLEN1]

If you are 100% sure that there are no air blocks and have correlated this fact by checking your heater is blowing hot then I suggest you check the viscous fan. By virtue of the fact that it cools when in motion but overheats at Idle it certainly sounds like this.

A viscous fan is filled with a silicon based gel that is fluid when cool but hardens when hot. At idle the air flow through the radiator is reduced and the little air that passes through the radiator starts to get very hot. This in turn solidifies the gel and locks the fan into operation whereby it increases the air flow hence cooling the coolant.

With the car off tie a piece of fairly strong cotton to one of the blades and the other end to something immovable in the car. Start the car and if once it gets to operating temp the cotton has still not broken then your fan is finished.

Next thing is your assumption that because it ran clean the system is clear . BIG MISTAKE.

These things gum up big time at the top of the rad and no amount of flushing will clear it. Either strip your rad (and yes this is possible) or buy a new one for +-£70 from Ebay. The fact that it was fine before you changed the coolant may just be coincidental or that you may have upset some lump of gunge that hadn't moved before.

You could well have a weakened rad cap, change this and see if it helps. The system needs to retain pressure to cool efficiently.

Fianally, at your mileage you are pretty much going on for the blown head gasket route. If during your draining/refill/bleeding process you allowed a hot spot to develop at a section of head that was about to go then chances are it has now done this. If you are losing coolant I suggest you suspect this

Thanks for speedy reply .Just remembered when I refilled system I filled it via expansion tank as I couldn't locate radiator cap as such on rad itself it doesnt seem to have one although I may be a complete moron ,I assumed it would have a cap for the rad in the traditional sense.

Didn't let it get to hot when filling flushing so hopefully head gasket is okay!

I am not losing any coolant either .Could you briefly describe bleeding process for this model as this could be the issue(air) my manual didnt detail it clearly it just told me to the run system with heater to max until thermostat opened then top up when level dropped at end of the process. I will try the cotton test in the morning when the engine is cold.How much is a new viscous fan and can anyone recommend a good parts supplier for this model is their a place that discounts Toyota parts for the older models.

What sort of mileage can I expect from this car I love it and really don't want to sell it it is part of the family!When I first bought it some of the examples I looked at had covered more than 200000 Miles!

[GLEN1]

If you are 100% sure that there are no air blocks and have correlated this fact by checking your heater is blowing hot then I suggest you check the viscous fan. By virtue of the fact that it cools when in motion but overheats at Idle it certainly sounds like this.

A viscous fan is filled with a silicon based gel that is fluid when cool but hardens when hot. At idle the air flow through the radiator is reduced and the little air that passes through the radiator starts to get very hot. This in turn solidifies the gel and locks the fan into operation whereby it increases the air flow hence cooling the coolant.

With the car off tie a piece of fairly strong cotton to one of the blades and the other end to something immovable in the car. Start the car and if once it gets to operating temp the cotton has still not broken then your fan is finished.

Next thing is your assumption that because it ran clean the system is clear . BIG MISTAKE.

These things gum up big time at the top of the rad and no amount of flushing will clear it. Either strip your rad (and yes this is possible) or buy a new one for +-£70 from Ebay. The fact that it was fine before you changed the coolant may just be coincidental or that you may have upset some lump of gunge that hadn't moved before.

You could well have a weakened rad cap, change this and see if it helps. The system needs to retain pressure to cool efficiently.

Fianally, at your mileage you are pretty much going on for the blown head gasket route. If during your draining/refill/bleeding process you allowed a hot spot to develop at a section of head that was about to go then chances are it has now done this. If you are losing coolant I suggest you suspect this

Thanks for speedy reply .Just remembered when I refilled system I filled it via expansion tank as I couldn't locate radiator cap as such on rad itself it doesnt seem to have one although I may be a complete moron ,I assumed it would have a cap for the rad in the traditional sense.

Didn't let it get to hot when filling flushing so hopefully head gasket is okay!

I am not losing any coolant either .Could you briefly describe bleeding process for this model as this could be the issue(air) my manual didnt detail it clearly it just told me to the run system with heater to max until thermostat opened then top up when level dropped at end of the process. I will try the cotton test in the morning when the engine is cold.How much is a new viscous fan and can anyone recommend a good parts supplier for this model is their a place that discounts Toyota parts for the older models.

What sort of mileage can I expect from this car I love it and really don't want to sell it it is part of the family!When I first bought it some of the examples I looked at had covered more than 200000 Miles!

Thanks again propnut superb advice any more gratefully received.

Cheers Glen

[propnut]

Take a read of the the Previa Heater post in this section where I outline the process.

The rad cap is the one on your expansion bottle, it is set at 13psi (0.9bar).

Bizzarrely enough there is a bleed nipple on these cars but it is a pain to get to and unnecessary.

Start with the cap and the fan and move on from there. You may want to take the shroud off the radiator and feel for any cool spots on the radiator that may indicate an inconsistent flow through it which in turn may indicate a blockage (WITH THE ENGINE OFF OF COURSE). It might be worthwhile checking your thermostat as well but as this requires draining the system try the other things first.

Like any car the mileage you get out of it will depend on how much you are prepared to put into it. As for spares, scrapyards, eBay and of course Toyota. You said you changed the belts make sure you didn't make the fanbelt too tight as this may inhibit operation and in the long run wear your bearings.

[GLEN1]

Take a read of the the Previa Heater post in this section where I outline the process.

The rad cap is the one on your expansion bottle, it is set at 13psi (0.9bar).

Bizzarrely enough there is a bleed nipple on these cars but it is a pain to get to and unnecessary.

Start with the cap and the fan and move on from there. You may want to take the shroud off the radiator and feel for any cool spots on the radiator that may indicate an inconsistent flow through it which in turn may indicate a blockage (WITH THE ENGINE OFF OF COURSE). It might be worthwhile checking your thermostat as well but as this requires draining the system try the other things first.

Like any car the mileage you get out of it will depend on how much you are prepared to put into it. As for spares, scrapyards, Ebay and of course Toyota. You said you changed the belts make sure you didn't make the fanbelt too tight as this may inhibit operation and in the long run wear your bearings.

You are a star thanks

:D Glen :D

[GLEN1]

Take a read of the the Previa Heater post in this section where I outline the process.

The rad cap is the one on your expansion bottle, it is set at 13psi (0.9bar).

Bizzarrely enough there is a bleed nipple on these cars but it is a pain to get to and unnecessary.

Start with the cap and the fan and move on from there. You may want to take the shroud off the radiator and feel for any cool spots on the radiator that may indicate an inconsistent flow through it which in turn may indicate a blockage (WITH THE ENGINE OFF OF COURSE). It might be worthwhile checking your thermostat as well but as this requires draining the system try the other things first.

Like any car the mileage you get out of it will depend on how much you are prepared to put into it. As for spares, scrapyards, Ebay and of course Toyota. You said you changed the belts make sure you didn't make the fanbelt too tight as this may inhibit operation and in the long run wear your bearings.

You are a star thanks

:D Glen :D

Further to the above checked and bled like heater post suggested .No different.I did notice that if I rev the engine when it starts to overheat this brought the temp guage down quite quickly and this was with the heater switched to cold on all settings.Would this further confirm the viscous fan or could it be water pump impellers/ circulation issue.

Thanks

Again

Glen.

[propnut]

If revving it brought down the temp even with the heater off then it can't be the head gasket so it must be a flow issue and unlikely the fan (but still not impossible). I would start with the radiator and the thermostat as these are the cheapest options. The radiators on these things block up and are only +-£70 off eBay.

[miti-babe]

Just my 2p worth...

My 1991 2.4 GL suffered overheating issues amos from the day I bought it (5 years ago). I drained/flushed the system - MANY times... I checked the thermostat - it had been cut in half by P/O (Git!) So now it has a nice new one... I checked the viscous fan (good tip that cotton check, Propnut..!!) I even removed the water pump to check the vanes on the impeller (no probs there...)

Then I concocted my own electric fan conversion... I've fitted a Rover ZX fan with a Honda switch fitted into the radiator drain plug... The fan works wonderfully and I'm sure it improved mpg, but it still overheated... Aaargh..!!

So, I bit the bullet and bought a new radiator - paid £95 for a double-core jobbie (twice as many pipes as the original).

Fixed... Totally... fan hardly ever switches on now... maybe twice a year... Max!

My 2p..? Change the radiator, you'll save yourself about 2 years of heartache and the constant worry that your head gasket is about to blow... or even the car's head gasket..! :D

HTH

Miti