Water system mystery

[MJS]

My SL SS had covered 900 miles with not a single problem - until now. Over the Xmas break it decided to blow out a fair amount of water with an appropriate rise in temperature. A roadside inspection found no obvious cause. Symptoms as follows:

 

1) No split hoses, loose clips, or any other leaks.

2) Topped up coolant, ran engine, no probs.

3) Partly drained system, then replenished anti-freeze.

4) Temp gauge rose to around 100°C (normally rock solid on 80°, no matter what), fan kicked in and stayed on, bottom of rad stone cold.

5) Obviously a suspected air lock, much remedial work ensued to get rid.

6) Thought I had cured it, but problem keeps coming back. I can get the water to flow properly if I loosen the bottom hose clip and bleed it there (the joint between the thermo housing J hose and the metal submarine pipe). Both top and bottom of rad get hot, as does the bottom hose, the fan cuts in and out, and the temp remains around the 80° mark. However, when I take it out for a road test the problem re-appears.

 

I have repeated steps 4 to 6 many times but don't seem to make any progress. My only two theories are a particularly stubborn slug of air which I successfully move about but must then settle in some part of the coolant system again at a later stage, or a suspect thermostat - but this unlikely in my opinion.

 

One other clue - if I let the engine idle the temp continues to rise, the fan kicks in, but due to lack of water circulating through the rad, stays on. But if I then raise the revs a little, the temp drops to a more acceptable level.

 

Any help on this puzzler would be appreciated.

 

Cheers,

 

Matt.

[Mick Day]

Check your thermostat as it may have failed - shut!!

[Allen Payne]

Dodgy thermostat?

[MJS]

OK, will do. Am I right in saying the thermostat is located in the black plastic housing to which the large J hose clips on to? Looks like it is secured to the block with a single small bolt.

 

Matt.

[Mick Day]

Yes. Check previous threads on how to remove the thermostat as it can be a bit of a bugger.

Mick

[Jason Plato]

Dont forget to raise the front of the car as high as possible when bleeding from the top of the rad , just in case you miss a stubburn air lock .

 

Dave

[Johnty Lyons]

Dave J has it, this is a well known problem. If you have a heater, open the valve ,then jack the car in the air so that a level line from the top of the header tank is above the top of the heater{[F*****G high mate]smile.gifyoull need a block of wood on top of a std trolley jack under the cruciform,} matrix run the car up to temp filling the rad NOTsad.gif through the header tank but through the bleed screw at the top hose position, also ensure that the bleed valve in the head beside the dipstick, is working [they gum up awfully easy ] and use only Rover pure 4yr antifreeze DO NOT DILUTE. Comma do a similar product.

 

jj

 

Edited by - Johnty Lyons on 29 Dec 2001 21:46:39

[CHRIS CLARK]

If you do have to go down the thermostat removal route, there is an easy way! I had to do this a while back when a large piece of solder jammed the stat--left over from the rad. manufacture?

 

Loosen the jubillee clip & remove the 'J'rubber cooling pipe from the back of the black plastic stat housing. Remove the top (only!) fixing that goes through the top of this housing into the block (8mm or 5/16th socket). By pulling/wiggling the housing rearward you can remove the unit (it's an 'O' ring that keeps it in place) to get to the three retaining bolts and check all is well/or not!

 

Good Luck!

[old captain slow]

If you have a heater you can bleed it from the top heater hose connection. Part warm up the engine (not hot!) so that a bit of pressure builds in the system. With the header tank cap still in place slacken the top heater hose connection. The free air should be pushed out.

 

Alternatively get rid of the heater - much better.

 

C7 CDW

 

 

[MJS]

Had another session with it today. Removed the stat and gave it the saucepan test - it worked OK. Put it all back together, raised the front of the car up and slowly filled the system via the top of the radiator. The 'problem' is still sort of there. I took it out for a spin and the gauge fluctuated between 80° and 100° (previously it never moved beyond 80°). My theory now is that it is due to the cold weather. Driving along causes such a cold blast through the radiator, the stat remains pretty much closed. When I slow or stop, there is a delay between the water temp rising and the stat opening causing the gauge to rise. Is this feasible? I'm going to try it with the nose cone partially blocked and see if this makes any difference.

 

Has anyone else experienced anything similar in this recent cold weather?

 

BTW, I don't have a heater fitted.

 

Matt.

[JP]

I've had a few temp problems with my K, mainly manifested by rapid heating up in traffic and seemingly slow activation of the fan.

I changed the thermostatic fan switch and the temp sender. The latter helped a bit. It only really improved when I took it to RRace for a service and they drained out all the coolant and replaced it with Comma Coldstream. The temp is fine now. On the way back from RRace I was stuck in a traffic jam from N to S London for about two hours - the temp rose to 80 and stayed there. In the current climate I find the car rarely gets hot enough - seems to run at around 65-70 most of the time, only reaches 80 in traffic queues. It may be the coolant change but I also accept that they may have flushed an airlock that I couldn't shift. Anyway, much better now, thought this may be of some help.

James.

[CHRIS CLARK]

My old 1400 SS used to suffer from overcooling in the later and early parts of the year (ie.winter). Made an aluminium rad blank that was retained by the rad. lower fixing bobbin/nut.Covered the lower third of it. Worked well, with no over heating and above all no overcooling either. Gauge sat at a constant 80* indicated when running.

 

Also fitted a 'Kenlowe' adjustable fan stat that meant I could manually set the turn-on temp. Had it set for a 90*. Worked well too and cut off fan at about 79/80*!

[MJS]

Well it appears I've cracked it - overheating seems to have been caused by overcooling. Did lots of checks etc, which all proved fruitless, then after an extended period of headscratching, came up with the theory that too much cold air was passing through the radiator and 'confusing' the thermostat. Tie wrapped a sizeable piece of card behind the grill to test my theory, and the gauge hasn't budged beyond 80°, no matter what speed or traffic conditions. Relieved there is nothing fundamentally wrong. When you think about it, the air intake of a 7 is vast compared to a 'conventional' car.

 

Mind you, driving at this time of year is a bit dire as it is now completely salted up.

 

Looking forward to summer.

 

Matt.

[Bob Corb]

This effect is caused by the amount of leakage through the thermostat and is well known. It is one of the main disadvantages of a bottom hose thermostat.When the engine is warming up the water in the rad circuit is stationary but under high pressure. This high pressure builds up against the thermostat which has a low pressure on the other side (at the pump inlet). Bottom hose thermostats need to have stronger springs for this reason.

 

Unfortunatley some stats leak more than others, when this happens the small amount of cold coolant passes over the wax bulb which chills the wax down so that even when the coolant temperature coming back through the bypass is passing 80degrees C the thermostat wont open. Coolant temperatures of 120 deg C have been seen before the stat will open.

 

I assume that your stat is particulary leaky and hence the problems you are seeing. Keeping the water in the radiator warmer by masking it off is reducing the problem. I'd replace the stat anyway. I haven't seen any problems with mine yet ('01 K series 1900miles). So I guess its down to cheap Rover leaky stats. There cant be that much variation in the rest of the coolant circuit??

 

Bob

[MJS]

Thanks Bob, you're reasoning makes perfect sense to me given the very crude 'fix' I have applied. If I buy a Unipart replacement stat, will this be of a higher quality than the one fitted originally by Rover, or can you recommend a particular manufacturer / supplier? Alternatively, I could just fit a slightly better engineered blanking plate which will have the same effect for less work - I think I could fill and blead the cooling system in my sleep now!

 

Anyway, I should stop driving it during these revolting winter months to help preserve the appearance, and also to keep some mileage in hand as I have a 6000 mile restriction on my insurance policy. I want to be able to have unrestricted use during the trip to Le Mans.

 

Thanks again for everyone's help.

 

Matt.

[Gridgway]

I was under the impression that a hole drilled in the stat was also used to cure this problem. However, I can't for the life of me work out why, so I must be mistaken, well I think anyway!

 

Graham

[Bob Corb]

I haven't looked at the stat itself recently. I thought the hole had a non return valve (aka jiggle pin) in it to let air bleed out during filling but not allow coolant to pass through during operation.

 

BC

[Gridgway]

yep, good point, I knew I had got it wrong!

Graham