C5 thp bleeding cooling system

[DSNL]

Hi guys
Is there a procedure for bleeding the cooling system on a 2001 Thp engine. I have a very hot top hose and a stone cold bottom hose.

Cheers
Craig

[xantia_v6]

Is there a procedure for bleeding the cooling system on a 2001 Thp engine.

I am guessing that you mean 2011?

I have a very hot top hose and a stone cold bottom hose.

That is the way it should be... assuming that the engine is not overheating.

The THP engine is, I think, self-bleeding. It is in the 308 anyway, you can see the bleed tube bleeding coolant into the header tank while the engine is running.

[411514]

I have a very hot top hose and a stone cold bottom hose.

Would this not suggest a thermostat stuck closed? Surely even in arctic conditions the bottom hose should be warm.

I have had this issue before, when the thermostat was near fully closed, preventing circulation of coolant through the radiator, and the top hose was being warmed only by heat conducted from the 'stat housing.

[ekjdm14]

Yes it does seem to suggest the thermostat being stuck, or even the radiator being blocked (although unlikely to be sedimented at this age, mixing OAT and non OAT coolants can cause it to congeal like a gel and not circulate so if the car has had a coolant change/top up recently this could be a factor)

[DSNL]

Thanks for the replys
Yes, Fat fingers mean it should be a 2011
No, the bottom hose should be at least warm. It is stone cold.
It has been getting slowly longer to get warm.
I did do a water change before the winter but it was fine afterwards.
It throws the cooling fan on all the time now.
When the bottom hose is squeezed it pushes water up in the header tank so pointing to the rad not being blocked.

Maybe I need to look towards a new stat then. I was just curious if there was a bleed point on these engines.
I remember the old Granadas (when I was a senior tech at Ford) used to have to be lifted on the front right to aid the air escaping.

[Paul-R]

With modern cars (mid 70s onwards!) having crossflow radiators the water pump is vital to ensure proper circulation of coolant. I remember (many) years ago an MGB which suffered from poor cooling. It took a lot of investigation until we eventually found that the impeller was loose on the shaft. As the radiator was vertical there was, at least, some thermoflow circulation.

Another case was on an A series engine. We found that a water pump which didn't have a deep impeller had been fitted to an engine which should have had the deep impeller design. I think that was a crossflow radiator but there was just enough coolant movement to cool the engine a bit although no reserve for heavy use.

Unlikely to be your problem but you never know.

[411514]

I was just curious if there was a bleed point on these engines.

I'm not familiar with the THP engine, but I would have expected there to be a bleed point somewhere (maybe someone more familiar can confirm this).

However, from your description of the symptoms, in particular that it has been getting slowly longer to get warm, it would appear that the thermostat is at fault (or at least is the main suspect). Although, that the engine has been slower to get warm would point to the thermostat being stuck open (rather than closed). Either way, it appears that the 'stat may be faulty.

Note - with most Cit engines (most likely the THP engine included but not certain) the coolant temp sensor for controlling the fan operation (amongst other things) is in the thermostat housing upflow of the thermostat. If the thermostat is closed, preventing circulation through the radiator and only allowing circulation through the heater matrix, clearly this will increase the temp of the measured coolant and so prompt the fans to kick-in.

My bet would be thermostat, but Paul's comments re the waterpump are certainly possible. I would change 'stat first given that it is the easiest, and then if this does not fix it turn to the waterpump.

How hot is the interior fan heater? If the air blown is hotter than usual, this would tend to indicate 'stat stuck closed, as the circulated water will only be being cooled by the heater matrix not the radiator. If the air blown is cooler than usual, this might suggest a lack of circulation even through the heater matrix, which would indicate faulty waterpump.

[ekjdm14]

Re: Granada coolant bleeding, I remember this also being the case with my Toyota MA70 Supra where many cases of blown head gaskets were immediately followed by yet another blown gasket just behind cylinder 6 due to people not "burping" the car in the prescribed manner. Most people thought you could get away extending the filler neck and relying on the weight of water to push the air out but it didn't work on the MA70 as the engine also was very slightly nose-down and the heater matrix is higher than the head too, so the air stayed trapped in the matrix & then worked its way behind cylinder 6 & melted the gasket again...

Anyway back on topic, it does sound like the thermostat has failed (I read the comment about taking longer to get warm as being the bottom hose had been taking longer to get warm before it finally stayed cold altogether.)

[RichardW]

I'll have a look later for the bleeding procedure, and a price / procedure for the stat. If it's taking a long time to warm up, but then running hot, it suggests the stat is stuck partially open.

[ell270390]

Thp engine has two bleed screws one on the pipe to the heater matrix and the other on the thermostat housing!! If vehicle has been into a dealer for temperature problems before it will most likely have the modified temp sensor which actually fits into the thermostat housing bleed screw if that's the case then you don't need to worry about that screw!!. Too bleed system keep coolant high in header tank and leave cap off, turn on heating and then raise and maintain 2500rpm this tells the ecu your bleeding the system! Then just wait until cooling fans cut in and your done. Have replaced quite a few thermostat housings for thermostat sticking!! Also is there any faults in the engine ecu?? The water pump on these engine are run off the aux belt via a friction wheel which is electronicly engaged when bleeding check it is running correctly.

[DSNL]

Thanks for all the replies
Got a new stat today (genuine. pattern parts are unavailable for a few weeks here)
The old stat housing had the sensor on the top of the housing and no bleed screw. The new stat has a bleed screw on the top and the sensor down the front.
This presents a small problem as the cable does not reach. I guess that as part of the mod there was an extension for the temp sensor.
Anyone actually know?

[Brian C5]

Hello I am new to this forum.

I too have a C5 THP with the same problem as you had (bottom hose cold) with the addition of the cooling fan not cutting in (even though I change the relay/ control unit) did changing the stat slolve your problem?

Brian