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Discussion Starter · #1 ·
Just when I thought my '86 Spider was running great and I vowed to keep my project list on hold while I enjoy driving it over the summer, I had cooling system issues over the weekend.

On Saturday I drove it about 40 miles without incident, except that I noticed something strange for the first time (not saying it never happened before- I just never noticed it). The temperature gauge moved up and down (as much as 30 degrees) while turning, but otherwise read around 180. Yesterday, however, I took it out again and, after only a short trip (about 1-2 miles), noticed the gauge reading over 180. Instead of continuing my trip, I decided to return home and test it around the neighborhood. After going up to about 200, it settled back down to 180 for a minute or two but then started creeping up, until I decided I better head home. By the time I got in the driveway, the red idiot light started to glow slightly.

The overflow reservoir remains at the max line and the neck of the radiator has some coolant in it. I never experienced any steam or boiling. I tried again tonight and had the same symptoms. The auxiliary fan is not turning on but I don't think that explains the problem. I am wondering if (actually hoping) it's the temperature sending unit (maybe it's really not running hot but it's misreading the temp). Unfortunately, I don't currently have access to a non-contact temperature sensor to determine the actual coolant temperature. Since the sending unit is cheap, I am thinking about just replacing it and seeing what happens.

Any advice?

Thanks in advance.
 

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Discussion Starter · #3 ·
Thanks Eric. I replaced the thermostat about 4 months ago since the old one was stuck open. Just feeling the radiator and tubes, it seems the thermostat was closed until it reached operating temp and then at least partially opened. I can't say if it fully opened though. It has worked fine, at least up till now. My thought was it likely was not the thermostat, but it wouldn't be the first time a fairly new part failed.

Wow, I had no idea you could get a non-contact temp sensor so cheap! I just emailed a few car guy friends to see if they had one I could borrow; if not, I will order one.
 

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the non contact thermometer can be also used to scan the radiator for cold spots, where it is plugged up. just hold it about 6 inches away and run it back and forth.
also, check for air in the coolant lines, if its got a bubble, it might be moving with turns.
cliff
 

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Discussion Starter · #5 ·
OK, so now I have a non-contact thermometer and am not sure where to take the temperature measurements. Should I be measuring the temperature of the sending unit itself (reads a bit lower than the temperature gauge) or the head at the location into which the sending unit is screwed (reads at or higher than guage)? There is a big difference (about 20-30 degrees) between these two readings.

Also, I can't measure the radiator temp while the car is running because it's blocked by the fan and shroud but it seems to read around 180 just after I shut it off (even though the guage reads higher); although the top of the radiator measures quite a bit hotter. The overflow bottle seems to stay pretty cool though.

I appreciate any help or suggestions.
 

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Discussion Starter · #6 ·
Sorry for all the questions, but something just dawned on me. I think I may have a separate sending unit (to the rear of cylinder 4) for the overheating idiot light. If that is true, then the problem is likely not with the sending unit for the gauge since the gauge and idiot light seem to be consistent (light goes on when gauge reads high).

I guess my problem may be the thermostat not opening completely (even though it was replaced about 4 months ago and was working fine until this past weekend). I am guessing if there's a water pump problem, it would be leaking or making a racket. Is it possible for am air bubble to develop over time? Any other thoughts?
 

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Check the grounds to the engine. senders will play up if they are not making good contact. I'd replace the sender to see if that solves the issue.
 

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Should I be measuring the temperature of the sending unit itself (reads a bit lower than the temperature gauge) or the head at the location into which the sending unit is screwed (reads at or higher than guage)? There is a big difference (about 20-30 degrees) between these two readings.
I'd try measuring at the thermostat housing. See if you can deduce if the t-stat is functioning (starting with a cold engine the temp would slowly rise as the metal heats up then suddenly rise when the t-stat opens).

Also, I can't measure the radiator temp while the car is running because it's blocked by the fan and shroud but it seems to read around 180 just after I shut it off (even though the guage reads higher)
That suggests the gauge (most likely the sender) is faulty.

The overflow bottle seems to stay pretty cool though.
As it should. Coolant does not circulate into/through the reservoir. It is simply a place to store extra coolant expelled when the engine heats up and return it to the engine when it cools down - keeping the cooling system full.

Is it possible for am air bubble to develop over time?
I guess it could. The coolant reservoir system is supposed to keep the cooling system full. Check the small hose that goes from the radiator neck to the reservoir. And consider replacing the radiator cap. If either the hose or cap is faulty it can allow coolant to go to the reservoir but not return when the engine cools down. Instead some air can get sucked in.

It'd be worth cracking open the bleed screw to see if any air escapes.
 

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Maybe you got some air in the system. Time for a bleed!

1. Remove vent screw on water pump.

2. Make sure vent screw on throttle body is tightened

3. Open heater valve

4. Pour 50% antifreeze/50% distilled water mixture through radiator filler until coolant flows out of water pump vent hole. Replace vent screw on water pump.

5. Resume filling radiator until full. Replace radiator cap.

6. Start engine and run at idle speed until engine is at operating temperature. Place a rag around throttle body screw and carefully open vent screw until there is only a stream of coolant coming out, no air. Careful- the water is extremely hot!

7. Tighten throttle body vent screw.

8. Let engine cool, top up radiator and install re-install radiator cap.

9. Fill reservoir bottle to maximum level shown on side of bottle and install reservoir cap.

10. Start engine and check for leaks.


http://www.alfabb.com/bb/forums/spi...bleeding-cooling-system-1986-alfa-spider.html

Dave
 

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Discussion Starter · #10 ·
Thanks all. I am away this weekend but think I will check the sending units again and test the thermostat in boiling water when I return, then reinstall it or a replacement and then bleed the system. I appreciate everyone's responses and will report back in a couple of weeks.
 

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Discussion Starter · #11 ·
Finally set aside a few hours for this. I think I have ruled out the sender units; the two units (one for gauge and one for idiot light) seem to be operated consistently and approximately at the temp that I read on an IR thermometer.

I tested the thermostat in a pot of boiling water and used an IR temp gauge. The thermostat begins to open around 180 degrees but only very slightly. When the temperature reaches 203 all the way up to boiling, the thermostat is open. The problem I have is I don't know how to judge whether it's FULLY open. I am attaching a couple of pics (I know how much everyone likes pics) showing the thermostat at temps over 203 degrees.

Can anyone let me know whether the thermostat is fully open?

If it's hard to judge, would it be a good idea to replace the thermostat since it's relatively cheap?

Sorry for the dumb questions, but I don't have much recent mechanical experience.
 

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Discussion Starter · #12 ·
Winner winner chicken dinner! Cliff, Eric and Dave, you were right- air bubble.

A guy at IAP confirmed the thermostat only opens as far as mine is in the pics above, so today I drained the coolant, refilled it, and bled the system. Sure enough there must have been quite an an air pocket because it took a lot more coolant to refill it completely than I drained out. I just got back from a long test drive and it seems that did the trick. It's running at normal temperature.

Thanks to everyone for your help.
 
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