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Discussion Starter #1
Hi all - I am asking this for a friend of mine (2001 model).
His MGF gets too hot when he drives far distances (let's say after an hour driving).
He has got a new temperature gauge and new radiator, but didn't solve the problem.

Any other ideas?

Thanks a lot!
 

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When you say 'Too hot', do you mean that the interior is too hot (heater stuck), or the engine is overheating?
A little more information i.e. symptoms, would help.
 

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Discussion Starter #3
When you say 'Too hot', do you mean that the interior is too hot (heater stuck), or the engine is overheating?
A little more information i.e. symptoms, would help.
Yes, the engine is overheating. The temperature icon goes right up, so consequently he has to stop.
When it is cooled down, after 10 minutes or so, he puts the fan on, so that it pulls the heat out of the engine.
 

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Initial checks:
1) is the coolant level up to the max mark on the header tank ?
2) Does the coolant need topping up regularly?
3) Does the radiator fan cut in when engine is v.hot?

Tbh - until it is sorted I would not drive it as overheating can cause these engines serious damage.
 

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Discussion Starter #5
Initial checks:
1) is the coolant level up to the max mark on the header tank ?
2) Does the coolant need topping up regularly?
3) Does the radiator fan cut in when engine is v.hot?

Tbh - until it is sorted I would not drive it as overheating can cause these engines serious damage.
1)yes, it is. When engine is cold the coolant is just below the middle seal line (the recommendation in the manual). When it has been running for a while it goes to the 2/3 mark (water has gone up).
2)no
3)yes

Thank you
 

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From what you say, the first thing to eliminate/sort the issue would be to renew the thermostat with a good quality new one - ensuring the system is bled properly once it has been changed.
 

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Discussion Starter #8
From what you say, the first thing to eliminate/sort the issue would be to renew the thermostat with a good quality new one - ensuring the system is bled properly once it has been changed.
Yes, thermostat was still good when they replaced the radiator 😊
 

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Sorry, I don’t understand ‘....yes thermostat was still good...’ .
Do you mean it was removed, and tested to find out at what temperature it opened at?
 

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Thermostats usually fail in the open position, so cause the engine to heat up slowly and run cooler. I'd be looking for signs of k-seal or other additive blocking the system (coppery residue in the header, cloudy coolant). If all nice and clean, try bleeding all the air out as there could be an air lock. Has work been done recently that required the coolant draining?
 

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I think it can be taken as an assumption that thermostats usually fail in the open position, particularly since they tend to open against the resistance of a spring. I would still advocate not assuming anything in relation to the thermostat until it has been proved to be serviceable - which it may well be, but....
 

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Sounds like air in the system.
Who fitted the new radiator, garage or DIY?
Did they bleed from all 3 bleed points?
 

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also check if there is a return flow in the header tank, if not then one or both of the jiggle valves will be blocked causing air pockets therefore blockages. if you rev the engineer the return flow should increase with the revs.
 

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2006 MG ZR +120 (HQM) 2004 MG ZR 105 (IAB)
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also check if there is a return flow in the header tank, if not then one or both of the jiggle valves will be blocked causing air pockets therefore blockages. if you rev the engineer the return flow should increase with the revs.
Is this normal on the F/TF?? I ask because I do not have experience of the specific situation in the F/TF.

I only have experience of the single jiggle valve in the inlet manifold on the 25/ZR, and in their case if you have flow back through the bleed pipe to the expansion tank it is an indication that the jiggle valve has got stuck open - in the 25/45 and ZR/ZS, there is not normally any flow back to the expansion tank through the bleed pipe.

The jiggle valve is designed to allow trapped gas to vent to the expansion tank rather than remained trapped and causing air locks. The inlet manifold jiggle valve in particular should not really allow coolant to flow through the bleed pipe - because it is at the pump/inlet end of the head, any coolant bleed off here will reduce the flow of freshly cooled coolant through to the rest of the head, and as is well established, there is often barely sufficient flow through the head to keep it sufficiently cooled to start with (as witnessed by the higher incidence of annealing and fire ring indentation of the alloy towards the outlet end and exhaust side of the head).

The OPs problem sounds most like a blockage - either air trapped by incorrect/insufficient bleeding (highly likely as there has been a recent rad replacement), or possibly a physical blockage - perhaps a build up of debris from the old disintegrating radiator, or possibly the thermostat - whilst thermostats almost always fail wide open (due to failure of the spring), if the car has had K seal or something similar used in the coolant system in the recent past (again, very possible if the rad had sprung a leak); it would not be the first time we have come across a thermostat in a K series engine becoming sealed shut by that stuff.
 

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there are 2 jiggle valves in the MGF, cant be sure about the tf as i only have an MGF, one is on the inlet manlet near the cam belt end, small ball bearing in a cage that should move freely to allow pressure back to expansion tank. the other is on the distributor side of the engine by the air filter, looks like a t-pipe connector/small barrel the size of the cotton roll. inside this one is another bigger ball bearing that allows flow back to the expansion tank.

the mgf is bought last year had had the head done 4 years previously even though it was less than 1000 miles ago i have had endless problems with intermittant overheating. i SHOULD have noticed when i viewed the car and looked in the expansion tank there was no flow coming back. after it overheated the day after i drove it back on the motorway on the hottest day of the year i started to try and solve the issue. i found both the inlet manifold jiggle valve blocked with paper like substance, even worse the other jiggle was so blocked i had to use flat end screw driver to unblock it. i now get variable flow back to expansion tank depending on revs, also it shows least the water pump is working. the position where the larger jiggle valve is if its blocked like mine it caused a very large air lock as the jiggle valve was at the highest point of the cooling system. i attach a photo the jiggle valve and you can see the stuff that was in there.

not saying this is the cause but its one of the things to check as we all know as brilliant as the k series engine is the slightest issue anywhere with coolling and you have trouble. good luck.

ps. i welcome any comments on wtf that pink paper stuff is that was in the jiggle valve, i expect its the cause of all my ongoing overheating issues, my local garage dont know. obviously some leak fixer, dont know why the chap i bought the car off had the car 10 years spent hundreds if not thousands on it but put that sh5t in it.
 

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