Over heating on 2001 (51MY) 3.0 V6 SE - S Type

[Tony Raspin]

I hope this reaches the correct destination, but apologies if it misses the mark.

Hi everyone. I'm reaching out for hopefully some useful info to help direct my garage to fixing an overheating problem on my 2001 (51MY) S type. Its a 3.0 V6 SE. The background. Bought car with an overheating event. Sellers garage indicated no head gasket issue but the radiator top hose valve had popped. Seller did not want any further costs so sold car. I had my garage replace the top hose, pressure test cooling system. Hose changed and car static tested running for 1 hour or so to settled running condition. Original fault codes P1299 and P1285 both reset. Car has been driven for 150 ish miles since this repair with no issues. Then today temp gauge rose over half way and further and shortly after the car went into fail safe mode. The radiator top hose valve has popped on the new radiator top hose like previous. Codes P1285, P1299 & P0133 revealed and reset and with only short distance I confidently drove home. Prior to second over heating the heater blower had been blowing warm air but for the my last 30 miles or so blowing much cooler air. So any suggestions welcome. Might the  heater valve failed and be causing the radiator hose to pop?  Many thanks for your time and help, Tony.   I'll answer any questions if asked or try to. Thank you cat owners.

[LairdScooby]

I have a probable fault in mind Tony but can you tell me, during your journey today, was it longer than the other journeys and did it involve motorway work and/or extended town work?

The heatr valve simply opens up to allow hot coolant to flow to the heater matrix, the system is designed so that if cold is selcted, the heater valve is powered to close and the system runs as normal, regardless of the position of the heater valve.

[Tony Raspin]

Hi Dave, journey was about 2 miles, park up, restart normally and temp gauge slowly passed halfway. I switched engine of in delayed traffic queue. Restarted and with next half mile gauge went into red and into fail safe mode. I was able to reset all 3 codes that allowed to drive normally and safely about further half mile home. Checked to hose and the value has popped with coolant splash. Driving all the time with blower temp set high but with coldish air. Like it for the last 30-40 miles that why I wonder if the heater valve is/has failed. It seems so coincidental being linked. Thanks, Tony.

[Tony Raspin]

If the heater valve fails to open / fully open might this create an overheating scenario?

[LairdScooby]

12 hours ago, Tony Raspin said:

Driving all the time with blower temp set high but with coldish air. Like it for the last 30-40 miles

You're low on coolant, did you top it up after the first episode?

12 hours ago, Tony Raspin said:

If the heater valve fails to open / fully open might this create an overheating scenario?

No, it doesn't work that way. As i pointed out a bit further up, the system is designed so you can use or not use the heater and it doesn't alter the engien cooling at all.

At the risk of making a snap diagnosis, i'd suggest the main radiator is either blocked or leaking if the head gaskets have been ruled out. Also worth trying the radiator expansion tank cap. I had a similar thing with mine where the coolant would be at the right level but the heater was blowing cold, it turned out the cap had gone weak so was allowing coolant to escape when it shouldn't which created airlocks. Because the heater matrix is so high on the S Type, that's where airlocks show up first. Worth trying one and topping the coolant up to the cold mark before you use the car each day to see if it's as simple as that :

https://www.ebay.co.uk/itm/403748795978

If nothing else, it will eliminate that as a possible source of coolant loss.

[Tony Raspin]

Hi Dave, thank you for all this advice. I'm sure I need a new top radiator hose fitted before anything else as the  casing "valve" stem round cap has popped and floats more or less in situ. I've found eBay item number:116062910765. Just a small point re what you say about the radiator maybe leaking or blocked, would this scenario have shown up earlier in the 150 or so miles I've driven since my garage fitted my replacement top hose, tested and filled with coolant. Or as with the unpredictability of cars taken its time to produce a repeat of the first coolant saga with the previous owner? Thanks, Tony.

[LairdScooby]

3 minutes ago, Tony Raspin said:

Just a small point re what you say about the radiator maybe leaking or blocked, would this scenario have shown up earlier in the 150 or so miles

Maybe Tony, it depends how badly blocked it is. It could also be that you've lost a lot of the cooling vanes between the radiator runners (that go between top and bottom tanks) which would reduce the ability to cool. Gentle driving at moderate speeds would reduce the need for cooling but going up a lot of hills, being stuck in traffic or motorway use would increase the cooling needs.

Before you shell out on a new rad, i'd suggest getting a compression test done and also a cooling system pressure test. If you can find someone that can flow test the rad as well then so much the better. It could be you were just unlucky with the top hose and the relief valve blew on the new one (i assume it was brand new?) because of insufficient coolant and an airlock becoming pressurised to the point where it popped the valve.

[Tony Raspin]

Hi Dave, thanks again for all your points of suggestion. So to recap, while I do need a top hose 100%, can I know if in your experience / knowledge and understanding of the rough timing of events i.e. heater blower blowing warm air then cooler air (on same (warm) heater / air con panel settings) prior to yesterdays overheating incident, that I do not need to change the heater valve and that this purely coincidental? Would you change it? Thanks, Tony. 

[LairdScooby]

It sounds to me that the DCCV (heater) valve is working as it should Tony. I'd sort the top hose, get the coolant level where it should be and repeatedly check it for at least 7-10 days while cold and top up to the level if necessary.

Because of the design of the system, it can take several days of shorter trips to get the coolant level to stabilise. I'd also suggest a new expansion tank cap, as linked to above.

[Tony Raspin]

Lovely Dave, many thanks, Tony

[Tony Raspin]

Hi Dave. I've just shone a torch down the coolant filler tank tube after removing the cap and I can see at the bottom of the tube the usual pinkish coolant. Surely with coolant loss I'd not see anything, or is this simply how the tube is designed in some way? Tony.

[LairdScooby]

You should be able to see the coolant in the coolant expansion tank Tony, no tube should be on it. I'll try and get a photo of mine tomorrow - my coolant is orange, i believe they changed coolant requirements over the course of production and different colours were used but i don't think pink was one of them.

[LairdScooby]

On 4/28/2024 at 4:33 PM, LairdScooby said:

I'll try and get a photo of mine tomorrow - my coolant is orange,

Here you are Tony, a day late but unexpected things happened yesterday!

You can just see the level of the coolant there, easier to see with the access panel lifted off :

In that one, you can see the coolant is level with the seam between the top and bottom halves of the expansion tank, this is the MIN cold level.

[Tony Raspin]

Hi Dave, thank you for being good enough to take time to take and send these pics. After the weekend settling of the overheating event I have decided to purchase a new top hose and heater control valve and have them fitted. I shall be putting forward to my guardian angel  a compression test done and also a cooling system pressure test. Also if possible flow test the rad as well. I think this is the best way forward for now. I've also bought a new  radiator expansion tank cap. Thanks again for all you help, regards, Tony.