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MG MGF Technical - Water Temp Gauge Woes


Driving home tonight and the traffic slowed to a crawl on the motorway. After crawling for about 5 minutes I pulled off the motorway and I noticed the water temp gauge was in the red. the oil temp was normal.

I pulled over straight away and switched it off.

I checked the dip stick and there was no white gunk. I removed the header tank cap and the coolant was ok. No oil in it and plenty there.

I let it cool a bit longer then drove it carefully home as it was only 5 minutes. The traffic was freemoving and it never went above half way.

I got it home and my dad came over to the flat to have a look. We ran it for while on idle and the front fan kicked in when the water gauge was about half way. But the gauge kept on rising. The engine bay fan kicked in but the temp was still going up. We turned it off just before the red. The oil temp guage was fine at less than 100 deg.


My old man reckon it's the thermostat that's knackered. Does it sound reasonable?

What about the brown temp sensor? I know that can cause problems?

Any other possibilities?
Bob Millar

Hi Bob,

I guess you've been running the warm-up test at tickover? Worth trying to see if sustained blips of the throttle start lowering the temp again. This would suggest restricted flow of coolant, rather than a total blockage. As your wise old man suspects, a sticking thermostat, or maybe a u/s radiator.

Worth bleeding the system thoroughly, a rad half full of air could feasibly give the same symptoms...

IIRC the brown sensor tends to fail in not giving a signal to the gauge, rather than erroneous/misleading readings.
Mike Hankin

I would suspect that either the radiator is shot or there is a vapour lock preventing adequate cooling Bob.

My next step would be to perform a coolant bleed - see http://www.mgf.ultimatemg.com/group2/common_problems/hgf_pages/coolant_bleed_procedure.htm

If there is no air to be seen, then suspect the radiator.

If the thermostat is at fault, the underbody coolant pipes will never warm up. Perform your idle coolant test again, open the bonnet, remove the front bulkhead shroud trim, and feel the coolant pipes to see whether they are warm or cold. The pipes are visible below the windscreen wash bottle.
Rob Bell

> If the thermostat is at fault, the underbody coolant pipes will never warm up

I'm gettting warm air through the heaters in the car?
Bob Millar

Bob,
When the thermostat is closed water still circulates around the engine and heating circuit so you would always get hot air when the engine is warm. Does switchin on the heater bring the temperature down?

What I don't understand is why would it make any difference if you are in traffic or not if the thermostat is stuck closed as water from the radiator can't get to the engine anyway.

Spyros
Spyros Papageorghiou

>> What I don't understand is why would it make any difference if you are in traffic or not if the thermostat is stuck closed as water from the radiator can't get to the engine anyway. <<

Good point Spyros. Everything is pointing to a problem with the rad - most probably corrosion, depending on age.
Rob Bell

> Everything is pointing to a problem with the rad - most probably corrosion, depending on age.


8 years
Bob Millar

It's toast Bob. Time to invest in a new rad. The TF item is better and made of alloy...
Rob Bell

> It's toast Bob

I believe the phrase rhymes with "Clucking Bell"

Also necessary for MOT at the end of the month

Flexi Pipe
4 Tyres
Rear Brake Caliper

and now we need a rad

Joy :-(
Bob Millar

> The TF item is better and made of alloy

Straight swop for old MGF part?

Cost? Roughly £150?
Bob Millar

Apparently it is a straight swap. Not sure of prices - phone Brown and Gammons/ Mike Satur/ MGF Centre for quotes. But 150 beer tokens sounds about the right ball park.

Might be worth removing the bumper to confirm the diagnosis first... armed with a camera of course ;o)
Rob Bell

I'll be dealing with it at the weekend. Getting a tow to my parents where I can get to work on it. The downside of living in a flat in Glasgow. No garage!!!
Bob Millar

Things that make you go hmmm.

Got the car to my folks on Friday night.

Removed the cowl under the bonnet, started her up and ran her for a bit. I opened up the bleed valves and a little bit of air escaped at the rad. Not much though. Ran her for about 25 minutes with no problems at all. Temp stayed stable just below half way on the gauge. Both the feed and return pipes to the rad warmed up. Coolant level had dropped a tiny bit so I topped it up. Seems it was an airlock. A thorough check showed no signs of any coolant leaks and the water and oil are fine. Very strange.

Then we turned attention to the brakes. The handbrake wasnt holding the car at all and I could pull the lever vertical. Rear calipers were removed and we discovered the handbrake mechanism on the caliper was seized so we cleaned them up, plenty of lube and worked it backwards and forwards for ages till it was completely free moving. I'm assuming internally it's on a spring loaded cam? Does anyone have any detailed schematics of the caliper just so I can see how it works?

Anyway the handbrake is 100% again which was nice. A little bit of time save spending £100+ on new calipers.
Bob Millar

Good result there Bob. But I would check the condition of the rad: I've had one let go on me a couple of years back... a right PIA.
Rob Bell

Hi Bob, I have had the same thing happen. Bumper to bumper traffic, and overheated. However it only took a few minutes for the car to cool down and I could drive off, although I got straight off the freeway.
What I realised later is that my fans arent coming on and I think this is cause. Hence why its only when I'm stuck in traffic that I've had a problem.
I had this happen once last year when I got caught in a traffic jam. I ended up having the car towed to an MG garage way over the other side of town. I was told a couple of days later that they couldnt find a problem but I still had a hefty bill. What had happened with mine was that coolant escaped and steam came out of the rear boot vents. I thought I had done another HG. The mechanic told me that there is an
release valve and thats where the coolant came from. I had lost very little however. And then since its been fine.
I want to work out the problem first before going near a workshop plus if its anything I can do myself, I'll give it a try (like the gear selector cable, that saved me heaps thanks to many of the people on this site and the wonderful instructions they have made available).
So if its my fans or my fan switch, how do I check this ?? Are there 2 fans, ione each side or just one fan. I've checked the fuses (both inside and under the bonnet - the fuses for anything titled FAN), they look OK.

Linda

Pretty straightforward checks Linda - detailed here: http://www.mgf.ultimatemg.com/group2/common_problems/hgf_pages/related_problems_overheating.htm

The problem you describe is either:
1. Fan fuses
2. ECU's water temperature sensor
3. Fan motor has seized

Good luck!
Rob Bell

Linda,

If you have aircon - which I assume you do in Perth - then you have two fans behind your rad.

What could keep them from coming on is a broken or corroded water temp sensor. I think Rob has a good instruction on how to reach that sensor on his website (He'll be along shortly to tell us...). What I do is regularly spray some contact cleaner on the electric connectors of that sensor, in order to maintain a perfect connection. A corroded connector gives a higher resistance which the ECU wrongly interprets as a low coolant temperature - hence the fans not being turned on.

Per
Per

Oops, I'm a slow typer... Rob had already been there...

Same morning routine as me, Rob, check the BBS before starting to work... ;-) ?

Cheers,

Per
Per

Yup! ;o) LOL
Rob Bell

This thread was discussed between 02/08/2005 and 09/08/2005

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