KV6 overheating.Coolant cap.

mileshawk56 · 13th September 2019, 09:49

My MGZTKV6 2.5 has run very hot of late and after investigation and testing showed no problems with the engine we have found the problem to be the coolant tank cap. Seemed unlikely so unlikely it wasn't considered initially and was discovered by process of elimination. A cap has been fitted supplied by Xpart and the temperatures are now spot on. One to consider if anyone has an overheating/hot running KV6. Chris.S.

SD1too · 13th September 2019, 09:59

Thanks for posting this Chris. It's always useful to remind members of this (as well as correct operation of the cooling fan) before the subject of head gasket failure rears its ugly head.

Sometimes however, it's just the two 'O' ring seals mounted on the expansion tank cap which flatten. They're not available separately from X-Part but something suitable can be obtained cheaply.

Simon

Blink · 13th September 2019, 10:34

Quote:

Originally Posted by SD1too

.... Sometimes however, it's just the two 'O' ring seals mounted on the expansion tank cap which flatten. They're not available separately from X-Part but something suitable can be obtained cheaply.

Viton O rings from Jack - https://www.ebay.co.uk/itm/133016723...m=133016723782

I fitted a brand new LR cap and the rings went flat straight away (these were standard rings, not Jack's Viton rings). Over-tightening the cap can almost certainly flatten the rings but I'd made sure not turn it past the first 'bite point' - and they still got flattened.

The owners manual page 145 says this: Ensure the cap is tightened fully after top-up is completed. It doesn't say what fully tight is and it doesn't mention over-tightening.

So it's difficult to know how much to tighten the cap on this car. Every other car I've had you just screwed the cap on until it wouldn't turn any further (i.e. it came up against the stops). The 75's cap seems to keep turning for much longer before anything mechanical stops it. Why?

suzublu · 13th September 2019, 10:49

Because it's spinning/tightening against the top washer, compressing it too far. I always apply vaseline to the rings and tighten just enough, and I have a 1.8

Yorkshire GOC · 13th September 2019, 10:53

In my 1.8t i swop out the cap every 12 months -

Blink · 13th September 2019, 11:10

Quote:

Originally Posted by suzublu

Because it's spinning/tightening against the top washer, compressing it too far. I always apply vaseline to the rings and tighten just enough, and I have a 1.8

But how do you know what 'just enough' is?

suzublu · 13th September 2019, 11:30

Quote:

Originally Posted by Blink

But how do you know what 'just enough' is?

Until you feel resistance, then about another 1/4 turn

Doesn't have to be really really tight, it's not going to leak

Any expansion vents out the side pipe

SD1too · 13th September 2019, 16:27

Quote:

Originally Posted by mileshawk56

My MGZTKV6 2.5 has run very hot of late ... the temperatures are now spot on.

Out of interest Chris, what figures did you observe for "very hot" and "spot on"?
Also, when the car is moving, is the temperature now stable within about +3˚?

Simon

marinabrian · 13th September 2019, 16:39

Quote:

Originally Posted by SD1too

Out of interest Chris, what figures did you observe for "very hot" and "spot on"?
Also, when the car is moving, is the temperature now stable within about +3˚?

Simon

117 degrees when "very hot" and 94 degrees running spot on

The phone call came in regard to this car couple of days ago, and given the fact it had expelled all of it's coolant over the engine bay, I surmised that the cap was defective, in all probability.

The suggestion was to force the fan outputs with T4 ( all three working satisfactorily ) vacuum fill the car with coolant, and fit another cap, which was carried out according to the official MGR technique, and lo and behold all is good again

So Chris could have saved a couple of hours labour by not buying a "genuine" cap from a source I'm not going to name

At least he had the presence of mind not to refill the coolant (5 litres) lost until the engine had cooled

Brian

mileshawk56 · 13th September 2019, 17:45

I accept Brians stricture regarding the genuine article but in my defence how do you know what is the genuine article? Even cost cant make that a certainty. I am however happy at this moment to accept I must tighten the cap until it stops and try harder to establish genuine articles. With this in view we must remember our cars have been out of production for 15 years with the a diminishing "official" support organisation and the growth of replacement parts of "apparent" similar quality. Its a lottery and in this instance I will hope I have a better chance of winning with the Xpart cap, note better chance not certainty! Thanks to all and hope not to reurn to this subject. Chris S.

13th September 2019, 09:49	#1
mileshawk56 Posted a thing or two MGZT Join Date: Jul 2015 Location: Berkshire Posts: 1,281 Thanks: 1,738 Thanked 299 Times in 216 Posts	KV6 overheating.Coolant cap. My MGZTKV6 2.5 has run very hot of late and after investigation and testing showed no problems with the engine we have found the problem to be the coolant tank cap. Seemed unlikely so unlikely it wasn't considered initially and was discovered by process of elimination. A cap has been fitted supplied by Xpart and the temperatures are now spot on. One to consider if anyone has an overheating/hot running KV6. Chris.S.

13th September 2019, 09:59	#2
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,382 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Thanks for posting this Chris. It's always useful to remind members of this (as well as correct operation of the cooling fan) before the subject of head gasket failure rears its ugly head. Sometimes however, it's just the two 'O' ring seals mounted on the expansion tank cap which flatten. They're not available separately from X-Part but something suitable can be obtained cheaply. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

13th September 2019, 10:53	#5
Yorkshire GOC I really should get out more....... Rover 75 connoisseur se v6 auto Join Date: May 2014 Location: Hull Posts: 2,069 Thanks: 1,842 Thanked 623 Times in 469 Posts	In my 1.8t i swop out the cap every 12 months - __________________ She came off the Longbridge Line on 20-05-2003 The Silver Machine was the 13th of 160 Rover 75's to come off the production line that day and is the 100th of 527 Starlight Silver Rover 75 2.5 V6 Connoisseur SE Auto saloons listed in the build records produced world wide.

13th September 2019, 10:49	#4
suzublu This is my second home rover 75 1.8 vvc club se wedgwood blue Join Date: Aug 2009 Location: Seaton Carew Posts: 26,921 Thanks: 65 Thanked 7,142 Times in 4,642 Posts	Because it's spinning/tightening against the top washer, compressing it too far. I always apply vaseline to the rings and tighten just enough, and I have a 1.8

13th September 2019, 17:45	#10
mileshawk56 Posted a thing or two MGZT Join Date: Jul 2015 Location: Berkshire Posts: 1,281 Thanks: 1,738 Thanked 299 Times in 216 Posts	I accept Brians stricture regarding the genuine article but in my defence how do you know what is the genuine article? Even cost cant make that a certainty. I am however happy at this moment to accept I must tighten the cap until it stops and try harder to establish genuine articles. With this in view we must remember our cars have been out of production for 15 years with the a diminishing "official" support organisation and the growth of replacement parts of "apparent" similar quality. Its a lottery and in this instance I will hope I have a better chance of winning with the Xpart cap, note better chance not certainty! Thanks to all and hope not to reurn to this subject. Chris S.