Hot under the Collar

[kilrwail]

My car must be mad at me. I took the Spider to help a friend examine a similar ’78 example he’s thinking of buying. My car must have gotten jealous, because it got very hot. I drove about 100 km at highway speeds after that and the temperature was fine – at or below 190 F. I stopped to make a purchase and had to drive through a fairly busy shopping district. After about 5-10 minutes I saw the temperature creeping steadily higher, so I bailed out and parked it in a shopping centre just as the needle hit the red. The electric fan was running, but it stopped after less than a minute.

I waited about a half hour until the engine cooled to just below 190 and started for home, knowing that I could stop whenever necessary if the problem recurred. Because I was able to keep moving at a decent speed, the temperature stayed normal – until I got held up at a traffic signal for a couple of minutes. Then it crept up to about 220 before I was able to get moving, at which point it dropped again. I parked in my garage and the fan was not running, although the temperature was about 200-210. I did something else for an hour or so and then went out to work on it.

I had decided that either the radiator was blocked or the thermo switch for the fan was malfunctioning. All four of the coolant hoses were hot. The rad has a small leak or two, which I had not noticed before, but the amount of steam coming out is very small. I’ll have that repaired. On the assumption that it might be a dirty rad, I flushed the system with Kleen-Flo and water and then filled it with normal antifreeze. When the system was full, I squeezed all four coolant hoses and saw the fluid in the rad rise every time, so the rad is clear and thermostat was open. I then started the car and let it run – and watched the temperature go above 200 F without the fan coming on.

So I’m assuming there’s a good chance that the thermo switch is pooched, but wondering whether it can be tested for static resistance and if so, what should the reading be? (I’m guessing it’s open at rest, so no reading.) After looking at the Vick catalogue, I tried their suggested test, which is to ground the black wire to the fan. If the fan runs, then the switch or its ground is bad. Well not quite, you need 12 V on the green wire too! The fan runs when so tested and it also ran when I put a jumper across the two wires normally connected to the thermo switch.

So I need a new thermo switch – does anyone have a spare? I will check with a local friend as well. Oh yah, it was a picture perfect day for a top down cruise and this did not spoil it one bit Sorry for the long post.

[punes]

I had the same issue...one of the wires entering the switch was not making contact all the time. When the temperature gets to the point when you know the fan should be running, jiggle the wires on the switch and see if the fan turns on/of. Thats how I figured out that my switch needed replacing...no problem since I replaced it. I hooked a switch to bypass the switch in case it ever does not trigger the fan.
That way I can turn the fan on at anytime if required.

79 Spider

[mdrburchette]

Peter, are you sure you haven't lost enough fluid to create an air bubble in the system? That's what it sounds like to me. I just went through this with my 71 and a leaking radiator. I've got an early model type but it looks like it changes after 1977. Do you want me to add one to my parts order and put one in your shoes?

[kilrwail]

Denise - There might be a bubble, although I doubt it. I had the rad cap as the highest point when I filled it and the level never moved. And the fan used to run for a couple of minutes if the temp was above 200. Now it doesn't come on at all, although the fan itself works fine. I'll try it again right now, but I think stuffing one in a shoe is likely wise. I haven't heard back from Chuck and he may be away. I'll confirm later tonight.

[kilrwail]

Denise – As usual, you may be onto something. I just ran it for a few minutes (maybe 10) and the engine temp climbed to 230, while the radiator reached about 125 (at which point my thermometer ran out of mercury) – and the fan did not come on. I don’t know the temp at which the fan should come on, but you’d expect the rad to be cooler than the engine, so maybe the switch is faulty as well as there being a bubble. And I jiggled the wires at the switch and its connector, with no effect. What’s odd is that when I changed the timing belt two years ago and drained/refilled the system, I had no problems with air bubbles. When it got really hot this afternoon and the fan came on, it didn’t stay on nearly as long as it used to. So for the sake of a $17 part (Vick 12-4694), I’d say it’s time to replace the switch. Antifreeze is cheap and I have to get the rad repaired or re-cored , so I’ll have a second chance to get rid of any bubbles. If you can get one and include it in the gift box, that would be great. Timing is not critical, of course.

[rlux4]

Not sure what you mean when you say the rad cap was at the highest point when you filled it. Did you have the car jacked
way up in front?
You should check that you are getting flow through the radiator when the engine is at or above 190°. Feel near the bottom of the radiator, if it's cool you either have a sticking stat or an air bubble (which would impede flow).
The easiest and surest way to top off the system is with a cooling T placed in the highest heater hose, back by the firewall.
If the temp sensor is not immersed in hot water, it will not trigger the fan. Which would be the case if your coolant is not circulating.
Ron

[kilrwail]

Ron - The front of the car is way up and the lower hose is hot. Squeezing the lower hose causes the fluid level in the rad to rise at the cap opening. But the radiator is not as hot as the engine, as verified with a thermometer. I suspect the thermostat is not opening enough. I'm going to change it as well as the switch, since it's well beyond its service life.

[mbouse]

sounds like you've diagnosed the problem to air pockets caused by a leaking radiator.

i believe i have a spare fan switch if you'd like to try it.

[mdrburchette]

Peter, I'll be ordering some parts this morning and will go ahead and get your t-stat and radiator fan switch.

[kilrwail]

Thanks everyone - I have the rad out now to get it re-cored and will change out the thermostat and switch, thanks to Denise There's a local specialist that others have used successfully, so that should work out OK.

[kilrwail]

I tested the old thermostat and it opened before water boiled (I don't have a big thermometer), going to a maximum of about 12 mm at 212 F (about 2-3 mm short of the ultimate). It may be good, but it's overdue for replacement anyway.

[mdrburchette]

Something else that may be worth mentioning, Peter. Of course, this all happened at the same time, which seems odd to me, but when my radiator developed a leak, I noticed my temp gauge edging to the hot side and was truly afraid I would do damage to the engine before I got it home. I replaced the radiator and had hell of a time getting the air out (internal t-stat conversion). Afterward, my gauge kept creeping to the red. I repaired the wiring to the head sender closest to the timing belt, but it didn't help. The infared thermometer was telling me the head and radiator temps were cool and the fan came on at the appropriate temp but my gauge kept showing too warm for comfort. I ordered a new sender. When I unplugged the sender, the temp gauge read accurately. Don't know why I keep thinking that first sender is the one that reads the temp but it's the one that pegs the needle. Any way, I'd unplug each of those to make sure they aren't causing a problem.

[kilrwail]

Thanks Denise. I'll have to try that after replacing parts and re-installing the repaired rad. Especially if there's still a problem! At this stage in the car's life (halfway?) there's no harm rebuilding the cooling system

[manoa matt]

There's also an in-line resistor in the wire that goes from the temp sending unit to the gauge. When the ends of the resistor corrode it causes the gauge to read hot due to the extra resistance. If you take that out and clean it off, the temp gauge should read more accurately.

[kilrwail]

Thanks Matt. This is the never-ending to-do list, isn't it? That's OK, I'd be bored otherwise.