Overheating

[bigjap]

i had a bit of a shock yesterday,i had to lift the bonnet, cos of a problem with it getting hot,running ok ,on my usual trip from poole to southampton,then got stuck in traffic and the temp started climbing slowly,just as i was going to pull over,the traffic cleared,and on the open road went down to normal,stopped in layby nothing really amiss,got back ok, today iv noticed temp creeping up in traffic then ok again, i know its around 25 here today,i think it may be the viscous fan,its not losing water the antifreeze always been changed regular.but fan will spin relatively freely without any resistance,iknow i have to check usual suspects, press cap, may have to flush out ,give rad hose thro,on my old ls there was an electic fan,but not one on mk4,anyone had probs with fans,have they got resistance normally ?

[cruisermark]

as far as can remember they dont have any resistance - i thought that was odd as when i changed my drive belt i though i had dislodged something but thats how they are?

Could this be a sign of a failing water pump i.e at lower engine speeds its not circulating the water quick enough?

[steve2006]

If you spin the fan by hand there should be some resistance and it should stop spinning within 2-3 blades, it should not carry on spinning freely as if it was on a straight bearing like the fan belt idler pulley for example.

[brendangeorge]

Hi Ray

Is your thermostat OK - if it does not open all the way you can have problems - also have you done any work on the cooling system lately? This can result in an airlock and cause problems. I think you mentioned the temp going up and down - I had this on my 430 and it was the thermostat and an airlock.

The airlock can cause intermittent cooling and if the thermostat does not open all the way when the engine reaches operating temp - same problem.

I hope it is something simple and not the water pump.

Good luck

Bren

[bigjap]

hi bren,thanks for that,i done the same trip back,and i turned off air con,and didnt have a prob, gauge stayed at normal,i suppose the water going around heater helped,it had the cambelt changed just before i had it,idont know if pump was changed then,but i had to keep topping up water for a while,nothing much,it just went to just below low,about every 2 wks,the last month its been ok,i suppose it may be pump,the fan has resistance when cold but spins freely when hot,i dont know if thats right,i ham going to clean out rad i think i will change thermostat and refill properly, work thro easy stuff go from there

[brendangeorge]

Hi Ray

You have the same problem as me - check the thermostat - check for an airlock and check to see if they put all the rad hose clips back on - they left the bottom one off mine and it caused a small leak.

You say the water level keeps dropping below low - this is what is called a ***** head trap and I fell in it (so do many others). The tank is not a reservoir for the water system it is an expansion tank only (you should never use any water - ever) - when you start from cold the thermostat is closed so the pump has to send the water somewhere (the expansion tank) - watch from cold and you will see this. If you keep filling the tank the pump will just blow it out at every cold start because when the water rushes in the expansion tank will overfill and the excess is blown out. You can have days of fun wondering where the water went :) However - be careful because I know nothing - make damn sure you do not have a leak - if you did I would expect your engine would get hot and stay hot so my money is on an airlock or thermostat problem - or water pump but pray it is not because it as much labour to change as the cam belt.

An airlock can happen if the people who did your belt did not follow the procedure for filling the cooling system and getting rid of the air - it is not a 1969 Ford Cortina that you tip water into the rad of it is a Lexus with a closed cooling system.

Best of luck

Bren

[bigjap]

thanks for help,i'd more or less thought it was airlock causing water loss,im going to change thermostat tomorrow and drain flush rad out and refill,

there is a label on top of exspansion tank telling you how to fill correctly,so i'll follow that,ive checked the rad not blocked in fins,so i'll do all that,and then have to do pump knowing my luck,but not end of world ,just wanna get it right

[bigjap]

just an update,iv drained system ,fitted new stat,flushed rad and system out,i have run hosepipe thro all rad fins the ac one and rad,refilled system,as per correct procedure, and its stayed at the correct level ever since,the engine temp stays on the second mark on gauge,i done 60 miles on fri no probs,with ac on ,which incidentally seems to be working better since hosing thro rad,it was ok ,but really good now,sun i had another trip,done 40 miles 30 c outside, got held up in traffic.after about 10 min the temp started to go up slowly,i turned the ac off, when it got to halfway,the temp went back to normal,when got going put the ac back all ok rest of journey.it seems to me the fan does'nt cool enough when every thing at full chat,the water still all ok,im thinking of changing viscous fan.anyone got any observations on this,water level correct, no probs normal running around

[ColinBarber]

I thought there was an electric fan in front of the AC condenser on all the LS400 models? Although it isn't for cooling the engine I think it does help draw more air through the radiator so you should make sure it comes on when the engine is up to temperature and the AC is turned on.

It may well be that the viscous fan has lost some fluid which means it may not spin as fast as it would do normally.

[The-Acre]

How hot is it getting anyway, how high does the gauge go?

[bigjap]

on my older lexus there were two electric fans in front of rad,this one mk4 has the air con rad /condenser then gap and then rad ,and then the viscous fan,no fan in front,i will have to investigate further

the first time it got hot it was getting close to the red,i just turned the air con off last time,to stop it getting too hot,id rather cook than the engine

[The-Acre]

on my older lexus there were two electric fans in front of rad,this one mk4 has the air con rad /condenser then gap and then rad ,and then the viscous fan,no fan in front,i will have to investigate further

the first time it got hot it was getting close to the red,i just turned the air con off last time,to stop it getting too hot,id rather cook than the engine

I would definitely see the fan as number one suspect, especially if it's cooling down when you move.