Mk4 jazz 2016 running hot

[Rickb]

My mk4 jazz running hot, engine red hot light comes on, looking under bonnet spitting out antifreeze no sign of fan running radiator was full that morning, air conditioning fan comes on when you press ac button. Changed bottom radiator coolant sensor took thermostat out and it does open in boiling water but did not check the temperature of water. How can I tell 100% whether the water pump is working and would it be a good idea to completely remove thermostat for a few days to see if that’s causing the overheating this is driving me crazy. When you push ac button the fan cycles on and off which is normal. When I look in fuse box I have a row of 9 relays and the 5th one in row switches aircon fan on and off. Both my coolant sensors are working and  tested.

 anybody know which relay switches the fan on when engine overheats? Or is it same relay that serves aircon?

Please please somebody tell me a definitive and easy way  to tell whether my water pump and thermostat working?


Anyone got a wiring diagram for the relays as there isn’t one in the car fuse box and not online.


I am at my wits end I think this will be my last Honda they are just too tight with service data some people can’t afford the exorbitant fees Honda charge and like to service their own cars at home. This is out of warranty now with 16,000 miles and has had a couple of things go wrong on it last week I changed the knock sensor now I don’t know whether I heed a water pump or thermostat ?..

[madasafish]

Temperature sensor for fan not working
Fan not working
Water pump not working.
Faulty warning gauge.

Work systematically through each, checking fuses, etc.
If you do not have a a multi meter then get one.

I would suggest you get it to a competent garage.

[Rickb]

Thanks madasfish, 2 temperature sensors have been changed one on block one on radiator fan works on aircon.
Water pump this i find very difficult to establish whether working how can I tell ?
I want to logically start to fix it but can’t get the information I need ! how many relays affect the fan ?does the fan run at single speed or multiple speed there must be someone who actually knows this out there.

[Rickb]

Update……
All relays checked…working. To do this it’s easy energise 2 pins of coil with alkaline pp3 battery and check continuity of other 2 pins whilst coil is energised. Some relays have diode on coil means relay will activate one way of battery.
All fuses checked
Coolant sensors checked resistance changes with temperature consistently on both…reading are within 5% of each other.
Thermostat has been tested once In hot salty water - opens but I did not check temp it said it should start at 78deg I’m hoping it’s this that’s erratic…

So chaps and  what’s my next move ….please don’t say scrapyard 😂 

Help help help

Anyone near Cuxton that can fix this?

[bobby boy]

Could the problem be with the wiring, or the connectors between the temperature sensor for the fan and the fan as it does not appear to work when the engine is over heating.

[monkeydave]

check the radiator pressure cap on the right hand side at the front of the engine bay, it might have a weak spring or bad seal and allow the car to boil over if its not holding pressure, its a nice cheap thing to try first as you say you had coolant spitting out under the bonnet - this would be my main culprit

the next would be the thermostat (but you have already checked that)

the water pump is the next culprit and even though honda water pumps have metal impellers not plastic that can break up and clog the cooling, i have heared that the impeller itself can stop spinning on the shaft (i have never experienced this though) so that would be my next call

does it overheat when driving or just ticking over?

so if it was me i would replace the radiator pressure cap first and then look at replacing the thermostat before changing the water pump

you seem to be having a lot of problems with such a new honda, have you replaced the coolant in the past or is it origional blue coolant?

also is your coolant low and if so check the drain plug at the bottom of the radiator isnt leaking or hoses or even the plastic top of the radiator where it joins the metal etc

so new radiator pressure cap first and i bet that will fix your problem, if not a new thermostat and if it still does it then water pump

[Rickb]

Hi Monkeydave, yes I think I can eliminate the pressure cap that’s been changed now so the pipes engine now gets so hot it circumvents the radiator cap pressure…

Whilst it’s getting to tropical temperatures the fan will eventually switch on but only at same speed as aircon cycle - should it be multi speed or high speed when it hits 90degrees I cannot possibly buy another Honda as getting information from Honda is like trying to squeeze juice out of stones, I quite like to do my own servicing it’s annoying that a water pump or a thermostat does not throw a fault code!

So how can I see if the water pump is working to sufficient level without taking it out out and how long to take a water pump out and replace Honda said they don’t sell them often and thermostat failure extremely rare.

It is the original blue coolant it has only 15,000 miles you could eat your dinner off the engine it’s so clean.

It overheats when driving and while it idles

My coolant not low up to neck of radiator

[Rickb]

Hi Bobby boy thanks for your help, I think it could be this but so difficult to trace wires back anyone know which coolant sensor does what on a jazz?

[monkeydave]

the only way to check the water pump without removing it would be to remove the belt and spin it by hand to see how it sounds and see if it has any resistance and seeing as you did the pressure cap and thermostat it is the next culprit especially if it overheats when driving

the time shouldnt be much more than when you did your thermostat to remove the pump

and honda are right, they wont sell many water pumps or thermostats as they very rarely fail (even at 68000 miles my 2004 civic pump was like brand new when it was changed with the cam belt)

how high does the coolant go up in the overflow bottle?

[ColinS]

Just a thought but is the Radiator getting hot?  If it is then I would say that the pump is working.

[culzean]

The actual thermostatic switch mounted on Jazz radiator will turn the fan on and off,  it is a simple device, normally a bi-metallic strip that closes the electrical contact when certain temperature reached. If I am reading the wiring diagram properly the same relay used to switch fan - the negative side of the engine fan relay can be grounded either via ECU output ( when aircon selected ) or by the direct acting thermostatic radiator switch ( power to positive side of relay coil is from a fuse that is always live, even with ignition off ).  You already know that the engine fan relay is working because it runs the fan when aircon selected,  so you are looking at purely the radiator mounted switch and its associated wiring, and the radiator metal work needs an earth return as well.  may be a break in wire in the plug or corrosion on spade terminal. 

If you know where the engine fan relay is plugged in you can get a muiltimeter and check for voltage on coil pin sockets -  ( where the two smaller pins on relay plug in ) one pin will have 12 volts on it, the other pin should read very low resistance ( less than a couple of ohms ) down to car bodywork,  if you get an very high or infinity reading down from pin socket to earth then the wiring or switch contact or both are FUBAR..

Has any work been done on radiator or has coolant been replaced recently ?  I replaced coolant on a car once and there was a big airlock left in the system,  the temperature gauge was hitting the top stop after a few miles,  but heater still blowing cold.    Another was to check if water pump working is to put heater on hot setting,  if it blows cold air then the hot water not circulating...

[embee]

Under normal UK driving conditions, moving freely and not stuck in traffic, the fan should hardly ever run (other than automatically with the aircon for cooling the a/c condenser). If it is overheating with the a/c off and normal free driving it's not likely to be anything to do with the fan per se.

First things first, is the rad clear and clean on the air side, no plastic bags etc stuck on it?

[culzean]

Try turning on aircon,  that means both large fans on radiators running so see if that cools down the engine.

[Kenneve]

Nobody has yet mentioned the possibility of a blown head gasket.
With the radiator cap off and engine at tickover, are there any bubbles coming up through the coolant?
If Yes, then that is a possible cause. 

[BadgerMk3]

How is the coolant level in your header tank?l

At a quick glance you refer to the coolant level n your radiator???