Sunday, September 14, 2008

Overheating - fixed

  • Change temperature sending unit (thermocouple)
Once again, the hurricanes got the best of me and I wasn't able to do anything to Bonnie Delilah (as she's known now; screw Shelly). I had an interesting car-related Saturday (detailed on the main page: www.arunluykx.com), though.

But now, the moment of truth. The new temperature sending unit (can we please just call it a thermocouple?) arrived, and lo and behold the gauge works again! It even displays the correct idle temperature - just left of centre. Taking it out for a spin the temperature did indeed go up when I applied the gas-pedal more, and cooled off at idle. Folks, the engine is running well again. The issue was -I'm ashamed to say- a lose wire, from the thermocouple, that was grounded by touching the frame.

One should note when replacing the termocouple that it is submersed with coolant, meaning that when you pull out the old thermocouple your car will start leaking coolant. I didn't feel like flushing the system again, so I just quickly removed one and replaced it with the new one (Beck/Arnley). The new one had a different bolt size and did not seem to fit particularly snug. However the temperature was fine and -once sufficiently tightened- it didn't leak coolant.

I also replaced the left window-winder (up till now I was using a little nub and my hand to pull up the window), and fixed the headlight switch (so I don't have to keep winding two wires together with my hands, almost burning myself each time). I tried replacing the key ignition but have had no success with that yet, so that'll be for next time.

Anyway, Bonnie Delilah runs safely and confidently again!

Sunday, September 7, 2008

Overheating - revisited (Or how I found the temperature sending unit)

  • Located temperature sending unit
One must understand that a car that has undergone as many upgrades as my MG has will have several loose wires, hoses, and other things leading nowhere. Because of all the upgrades its not entirely obvious what each fuse belongs too, that is after you figure out the confusion that is the stock 5 fuses that make no sense whatsoever. I can't believe the British managed to evolve to this century with this kind of horrible electrical engineering.

As such, I discovered today why the temperature gauge hasn't been doing anything. Apparently one of the loose wires under the hood is the temperature gauge wire.This explains why the engine was running ice cold all of a sudden, and the 'off the gauge' heat is probably due to the fact it was grounded somewhere, touching the alternator or some part of the body. Duhhhh. All that work for nothing!

Well, not really. The coolant was almost entirely anti-freeze, and the thermostat would have had to be replaced at some point anyway. Also I confirmed that the waterpump was OK - this is something I would have been worrying about all the time.

I reconnected the wire to the temperature sending unit, which by the way is under the thermostat housing sticking out above the alternator (no thanks to the internet here, where nobody could give me a straight answer). It's got a little contact point sticking out that should have a wire connector attached to it. See the image below for the location of the temperature sending unit (without wire connector- it broke off). This is the only picture of the thing's location on the internet.

Unless I'm completely wrong, which I highly doubt.
Correction: I just found a better image of this. Note that this picture was taken after the time of writing, and so what I said was actually correct... ;-

Refitting the cable (testing it first by touching ground to see if the temperature gauge went back to hot) I ran the engine for a while, but couldn't see any difference in temperature. I'm ordering a new temperature sending unit (about $20 on Rockauto), which I'll refit next weekend. I'm also having keys made for the locks this week. A new window winder and ignition key is in the mail already. So hopefully next weekend I'll be able to take Bonnie (it's Bonnie, screw 'Shelly') home, when she'll be fitted with some nice new tyres. That is, unless another hurricane sets me back a day.

Monday, September 1, 2008

Overheating (changing the thermostat)

  • Replaced thermostat and gasket
  • Flush coolant
Labour day. This generally means barbecues, getting quite drunk, and relaxing in the shade during a pleasant late-summer afternoon. For me, however, it meant hanging over a smoking engine inhaling various gasses while trying to figure out why the engine was overheating. And I loved it.

The manual suggests several causes for the overheating I leave to the enthusiast to check out. I had narrowed down my options to these possibilites:
  • Failed thermostat
  • Failed pump (either the propeller came loose or the bearing broke)
  • Clogged radiator
  • Too much anti-freeze in the coolant
As the engine oil levels were fine and clean I did not bother doing another oil-change. Another quick check would be the accessory belt tension (slipping causes bad water-flow), which was fine and the belt was new.

I started by testing out the bearings on the water pump. To do this I removed the accessory belt and turned the pump manually. I heard a squeaking sound when I turned it, but it did not shake and so I assumed the bearings were fine. There was also no leakage from the unit itself.

To look at the thermostat and do further testing on the water pump I needed to flush the coolant. Easy, in general, except for some reason my radiator doesn't have a drain plug! I couldn't find any help on the internet on the topic so I ended up removing the bottom hose and draining it like that. The coolant was filthy, and very green indicating a large amount of anti-freeze. This could be the problem. I flushed the engine with clean water for a few minutes before proceeding.

While it was without coolant I decided to take a look at the other parts at the same time. My reasoning was that the water-flow was somehow restricted, which was causing the overheating.Turning the water-pump sent water out the bottom hose, so it wasn't that (although the propeller has been known to come loose at high temperatures, and the engine was cold when I was testing it, but this is very rare). In the end I decided the thermostat needed to be replaced.

31 years can take a toll on some parts, so after removing the upper hose and the three bolts holding it in place (see right picture, circled in red) I needed to use large amounts of a solving fluid (like WD-40) and a small crow-bar to get the thermostat housing off (see left picture, thermostat indicated with arrow). It was difficult, but I got it off. The thermostat looked fine, but I replaced it anyway with a part I bought at Advance. I also bought a new gasket.

Removing the housing I scraped away whatever was left of the old gasket and put the old thermostat aside to test it out later. The new gasket was installed (though it looks symmetrical, orientation matters! By the way this goes on top of the thermostat) and the thermocouple replaced. I also filled up the coolant again with 75% water by pouring it directly into the engine while the thermostat was out. The remaining coolant/anti-freeze was entered after the radiator burped and the engine was running.

They say in old cars that when you fix one problem another ten arise. This car does not defer tradition. I don't know if the engine is overheating anymore because the gauge doesn't move!!! I stays below C all the time, even after driving it around for a while. All the other gauges work normally, and no amount of tapping gets this to even jump. The old thermocouple was submerged in boiling water later on to see if it was defective, which it wasn't (it opened up just before the water started boiling, around 195F/91C ). It is however possible that that the opening was not sufficiently large to let enough water through. I'll be testing the gauge and the sender unit out next.