Technical Radiator top hose hot, bottom hose cold

[euro]

Punto Mk1. -- Radiator top hose very hot, bottom hose cold and the car keeps boiling its water? This is the same even after a long run.

I have bled the radiator but its still doing it. Any idea why the top hose would be very hot while the bottom one ( and also the bottom of the radiator is cold while the top of it is hot). Its a new radiator by the way.

 

[bandido41]

Sounds like your thermostat is stuck closed and not allowing the water to circulate through the motor.

 

[euro]

Sounds like your thermostat is stuck closed and not allowing the water to circulate through the motor.

Thanks, I had a suspicion it could be that. The odd thing is... the top hose is connected to the thermostat housing but its the one thats getting hot.

 

[kristouk21]

had similar prob with mine.. mine was over heating..

here is a link to my post last week might find it of some use
https://www.fiatforum.com/lets-talk-fiat/144778-fiat-punto-overheating.html

 

[euro]

had similar prob with mine.. mine was over heating..

here is a link to my post last week might find it of some use
https://www.fiatforum.com/lets-talk-fiat/144778-fiat-punto-overheating.html

Thanks. I have done a million bleeds but its not helped. Took the thermostat off yesterday (Its no small job on a diesel, thats for sure) and have a new one on order. Hopefully that will sort it.

 

[kristouk21]

good luck.. if not then prob could be a pump. (if the water aint circulating)

 

[euro]

good luck.. if not then prob could be a pump. (if the water aint circulating)

Thanks mate. Its hard to be certain if its circulating to be honest but the heater was working well throughout so I'm taking that as a sign that it was getting pumped round.. fingers crossed.

Looks like the thermostat could be over £50 though!! You have to replace the whole housing which has 4 water hoses coming into it and 2 sensors attached.. 1 for the temperature light and 1 thats connected to the deisel high pressure pump.. for cold starts I assume.. it took me about 2 hours to get it off. Fiats jubillee clips dont help in tight spaces!

 

[kristouk21]

if your finding it a bit tight remove the battery... an ht leads i dnt have a diesel but im sure layout is pretty similar.. i practiced on a 1.2 punto (petrol) i think the themo houseing for that was £8.. thats the whole thing... (thermo housing and switch) (this 1 had 1 outlet on the housing)

i got a price for a thermo on mine they said £22 (could be switch only) mines a 1.6 sporting. petrol(95) mine has 2 outlets on the housing. 1 return to radiator an other to heater matrix.

for yours i think you will be looking at around £35 including gasket..... might be with yours it might not need new housing.. the switch might be separate but u need to remove the housing to get it..

dnt go to fiat they will charge through the nose for it. try PARTCO.. or a motor factor. give them the model year engine size etc.. also have a look at yours make sure wen u go to pick it up its the right 1...

{i know you say you have bled you system... but to be honest it dnt sound like thermo... on your car there should be 2 valves one top left hand side of your radiator and another on pipe leaving the thermo housing into or towards the car. while engine is cool start engine and start with the valve near the housing.. just twist it and wait till u see water.. warm air exits through the top pipe which is were housing is if that pipe is hot then i would say its working. cold pipe is bottom that runs from rad into the engine... there could be a air lock in you rad.}

 

[euro]

Hi,

The thermostat is off the car. I did it yesterday.

As you suggested I removed the battery and the tray.

The housing and thermostat are all 1 unit sadly which is bad planning for a part that can often need replacing. I had alook through the Haynes manual and as you say, the petrol one is nice and simple to replace but the diesel one is not so straight forward

I just hope it fixes the problem. Not easy to test the old one as its part of a dirty great casting.. good old FIAT ! I had originally thought the thermostat was between the top radiator hose and the block but once you get it off you can see that its actually between the bottom hose and the block.

New thermostat should be with me on thursday so i can get everything put back together. If its still the same I think it will be water pump next.. I am trying hard not to let the words head gasket get into the conversation

Thanks for the reply by the way

 

[mark16v]

try putting the thermosta in a bucket of warm water see if it opens, if it dose its not that.

 

[kristouk21]

needs a bit more than warm water... place the thermo in a pan of water.. start to boil it slowerly.. wen the water reaches the temp it should be it will open.. if not its bust!! if it does then it not your thermo. if you cant fit the thermo in a pan or bucket then a steamer used for stripping walls... that normally do the trick.. dnt use a blow tourch (this would mess it up) the heat is to intense...

dnt think along the lines head gasket... unless the car overheats that bad the fan on your rad wnt keep it cool enough.. u mention the pipe stays cold on a long journey so im assuming it dnt get that hot it cuts out....

if it aint your thermo then possibly pump like i posted earlier.

 

[arc]

edit - just noticed you have a diesel, i don't know that engine so don't know how relevant anything below is!

if the top hose is hot, and the bottom hose is cold - why would it be the stat? think about the water flow.. the stat controls waterflow out of the head and into the rad. if the stat was stuck closed then there would be no flow into the top hose and it wouldn't get hot. it couldn't get hot because no water is flowing into it.

if the top is full of hot water and the bottom is cold, then there is a flor problem. be it pump or a blocked radiator.

sounds to me like the pump is bust to. the old ones used metal blades on the impeller that drop to bits, meaning it can't pump water anymore.

 

[Mdeko]

edit - just noticed you have a diesel, i don't know that engine so don't know how relevant anything below is!

if the top hose is hot, and the bottom hose is cold - why would it be the stat? think about the water flow.. the stat controls waterflow out of the head and into the rad. if the stat was stuck closed then there would be no flow into the top hose and it wouldn't get hot. it couldn't get hot because no water is flowing into it.

if the top is full of hot water and the bottom is cold, then there is a flor problem. be it pump or a blocked radiator.

sounds to me like the pump is bust to. the old ones used metal blades on the impeller that drop to bits, meaning it can't pump water anymore.

I agree. . but also the radiator takes in hot water at the top, cools it (therefore through the rules of physics it goes to the bottom of the radiator) and out the bottom hose alot cooler, so the bottom hose would be cooler than the top hose (i would of thought anyways)

 

[euro]

Thanks for the replies.

On my engine the thermostat is between the bottom hose of the radiator and the engine block. When the car has overheated and I check the hoses the top one is always very hot but the bottom one is always cold. the same applies to the radiator (which is new), its very hot at the top but cold at the bottom. If the stat was working and the engine is overheating why wouldn't i feel the bottom hose at least getting warm?

The fan switch sits around the centre of the radiator and if i feel the metal around it, its always cold so it doesn't know the rest of the engine has overheated and hence the fan does not come on.

I'm leaning towards the pump ( well 1 day i think pump, the next i think stat) but as the thermostat is easier to get too I am going for that first despite it costing almost £50 ! I havent found a fail safe way to test the pump but as the car heater hoses are both getting very hot and the blower is blowing out hot air I have assumed (maybe wrongly) that there is some sort of flow taking place.

 

[Mdeko]

Have you rules out a blocked radiator?, When was the coolant last changed/flushed out?

 

[euro]

Have you rules out a blocked radiator?, When was the coolant last changed/flushed out?

Radiator is brand new from Fiat. Coolant was changed when i fitted the rad.

The car was stood for about 7 months prior to these problems, In fact it was recovered here because it had overheated (radiator had rusted through and leaked out all the coolant) and then was not touched for the 7 months.. I decided to get it going, had a fair bit of trouble with fuel and none running etc which is now resolved but now it has this overheating problem. It could be that the thermo has jammed shut over the 7 months I guess..

 

[kristouk21]

mine was laid up for bout same time.. it turned out mine was air! replace the thermo an see how u get on.

i have to replace 2 ball joints and discs and pads im never leavin a car on the path again lol.

 

[euro]

mine was laid up for bout same time.. it turned out mine was air! replace the thermo an see how u get on.

i have to replace 2 ball joints and discs and pads im never leavin a car on the path again lol.

Good luck, the british winter and italian metal doesn't mix that well!

Thermo arrives today so I will soon know my fate

 

[euro]

Fitted new thermostat last night (cost me £52 !!!). The diesel one is a mare to fit. 5 hoses and connections to the fuel pump etc, then refilled and bled the system.

I took it for a run today.. very hot day and left the heater off etc to give it max stress. so far no boiling up and the bottom hose is now getting very hot .. well almost as hot as the top one so hopefully its finally sorted. Time to fill it with antifreeze I guess as its got water in at the moment as its already boiled up 2 lots of antifreeze.

Thanks to all for your help. FIngers crossed I'm not back in this thread.