overheating

[gillorasp]

The other day I had a 100 mile run in my v6 zt. All was fine except the fan seemed to be on more then normal. Being a hot day didn't think much of it. Got home after the run and turned the car off for an hour. Decided to pop to the shops. After about 5 miles I noticed the temp gage was in the red!! So turned the car off and waited 5 minutes. Started and drove and a mile later happened again.

I then opened the bonnet and felt the radiator which was stone cold. The top hose on the radiator and the header tank were also stone cold. I then opened the cap on the tank to find a lowish fluid level but I idled the car at 2k. At this point the fluid came out the top of the header tank. I then put the cap back on and drove it for 5 miles with no overheating problem. I stopped and checked the radiator and top pipe which were now red hot.

I later checked the coolent level and had to add around half a litre. Since doing this the fan rarely kicks in but I tested it and it does kick in at 100. The last 2 times iv drove and stopped iv checked the coolent level and iv had to top up about 100-200ml each time but haven't had any overheating problems.
Iv looked into the v and can't see any signs of leaking coolest. Just wondering if anyone had any ideas. What might be causing the problems.

[StewartIngram]

I've just been hijacking this thread with something that sounds similar:
http://www.the75andztclub.co.uk/forum/showthread.php?t=220071

Basically I found the fault was the small dia hose that commects to the side of the filler neck on the expansion tank. Though this is of an o/d about the same as a little finger, the hole through the plastic to the neck is only 1mm ! This was blocked on mine, and it took me about an hour to clear it through. Once done, everything ok.
Seems that the water in the radiator expands when hot, going through this pipe to the spare space in the header. Once the radiator cools it will return from the header.
If I've got this right, with a blocked pipe, the radiator pressure increases, with water going the other way round the system it is forced out of the expansion filler cap. This in turn allows overheating. Whatever, clearing the 1mm hole cures it! Difficult to see unless you remove the header tank though.

Stewart

[T-Cut]

If I've got this right, with a blocked pipe, the radiator pressure increases, with water going the other way round the system it is forced out of the expansion filler cap.

The small bore hose to the filler neck is important, but it doesn't operate as you suggest. It's primarily an air vent from the head and the radiator top. However, air can only come out of the small hole in the filler neck when the pressure cap is removed. It's to vent those spaces during a refill and bleed. When the cap's back in place, the outlet hole is blocked off between the two o-rings on the cap. When the engine's running normally, nothing can pass through the small hose. However, after a hot engine shut down, super-heating/over-pressurisation can occur in the head, which is relieved via the pressure in the hose lifting the main relief valve in the cap. At least it does in the 140kPa cap. The earlier 100kPa caps are different internally.

TC

[gillorasp]

Just an update. Took the 5 mile trip to work this morning. Car got up to temp and stayed bang in the middle. Just checked the fluid and it's stayed put at the max. Hopefully it was just an airlock. I think I need a longer run with temps.up to 100 tho to really test. Iv only owned the car a month or so I'm just wondering if the 0revious owner was running it around with no fluid on it and me adding a little bit when I first got it has caused a airlock.

Will report back after more road miles.

[Stag>75]

Just an update. Took the 5 mile trip to work this morning. Car got up to temp and stayed bang in the middle. Just checked the fluid and it's stayed put at the max. Hopefully it was just an airlock. I think I need a longer run with temps.up to 100 tho to really test. Iv only owned the car a month or so I'm just wondering if the 0revious owner was running it around with no fluid on it and me adding a little bit when I first got it has caused a airlock.

Will report back after more road miles.

There is a documented bleeding procedure for the V6. You will find it somewhere in the forum but basically you need to unbolt and raise the tank, running the engine so the thermostat opens and then bleeding using the bleed screw in one of the hoses.

[gillorasp]

There is a documented bleeding procedure for the V6. You will find it somewhere in the forum but basically you need to unbolt and raise the tank, running the engine so the thermostat opens and then bleeding using the bleed screw in one of the hoses.

Thank you. I will get on this hopefully when I get home tonight.

[cooper.mg190]

Mine did this after purchase,
I did a full service, and changed the coolant, bleed the system from the bleed screw (on the top of the hose next too the Throttle Body). as I don't have access to a vacuum system,
I checked the coolant everyday for about two weeks. And re bled the system, haven't had any problems, no coolant loss, and no Red light for the coolant temp.
I've check my coolant every other day, since. No issues. :)
Hope this helps.

[SD1too]

There is a documented bleeding procedure for the V6.
And here it is (http://www.the75andztclub.co.uk/forum/showpost.php?p=1547805&postcount=15) Matt (gillorasp). Follow the procedure exactly; don't cut corners or miss anything out and if you have an air lock it will get rid of it.

If you still have problems check the small bleed orifice in the header tank neck as described by StewartIngram. Whatever it does, it needs to be clear and not blocked.

Simon

[gillorasp]

Thank you for all the help what a great forum this is. I will bleed it tonight. It looks like the last owner had a few issues and put k seal in the coolant. Since topping up 2 days ago the level has been constant no further loss. Done around 150 miles since so hopefully if was just low when i bought it. I did notice a Little bit of white under the oil filler cap yesterday morning but it was 6 degrees outside so I think it was just condensation.

[SD1too]

It looks like the last owner had a few issues and put k seal in the coolant.
Oh dear. :mad: I would drain your cooling system completely then, not forgetting the left-hand bank cylinder block drain plug (see procedure), and keep your fingers crossed that most of it comes out.

Unfortunately Matt, Mr. Previous Owner was misguided. The KV6 head gaskets are not susceptible to unprovoked failure. The "issues" you described would have been due to other causes of a less serious nature.

Simon

[DMGRS]

Best to put some kind of flushing agent in the coolant to help dislodge the K Seal too - nasty stuff that is.

[SD1too]

Best to put some kind of flushing agent ... to help dislodge the K Seal ..
Any suggestions Mat? ;)

Simon