355 Temperature Light

Just a guess, but perhaps low coolant in the overflow tank could also trigger the light?

 

Seems to me if the car is cold there is no expansion of the coolant due to heat. I would check that the overflow tube is clear of any obstructions.
As the manual states, you should have about 1-2" of air space before hitting the coolant level in the reservoir, when all is cold.

 

There is no low coolant indicator or sensor that I know of. Rather disappointing especially given the damage that could be caused from overheating (and the fact that the originally spec'd 30 amp radiator fan fuses like to blow!)

 

The guage and light do not work off the same sender. If the water and oil temp guages read normal and the fans cycle on and off I would certainly suspect the sender unit that turns on the light.

 

"More or less" under the coolant overflow tank (both). The sender closest to the cockpit is for the guage reading. The sender closest to the rear end of the car is for the high coolant temp light.

Intermittent light seems to confirm a bad sender or the wire to the high coolant temp light grounding out somewhere along the way to the guage.

 

I had no idea there was a light for overheating of coolant. The front sender as mentioned is for the Veglia gauge. The one on the rear of the engine, adjacent to the oil filter housing is the coolant temp sender for the Motronic. Does this one also trigger the light? If it is, I would suspect it should also be triggering the "check engine" light if it is detecting an overheat situation...no?

 

I think the general consensus is if the radiator fans are blowing the 30 amp fuses regularly, then it is time to consider replacing the fan motors. Usually you will also notice a drop in engine idle when the fans come on as well, from the excess current they are drawing. New fans, and no more blown fuses or idle drop.

 

It's my understanding (and I could be wrong!) the sender that turns on the right-hand fan (via the Motronic) is at the bottom of the oil tank. I believe only the LH fan is controlled by coolant temp. and the RH only by oil temp. even though both sides have coolant radiators.

If you look at the water temp. guage with a flashlight you will see there is a small circle that will light up (just like the one on the oil pressure guage that lights up when there is low/no oil pressure). That one lights up every time you turn on the ignition. You will never see the one in the water temp. guage light up unless the engine overheats.

I would be surprised if they got sophisticated enough to integrate the high coolant temp. light with the Motronic/CEL system. I think it's a "stand alone" device that just grounds out to light the lamp (haven't confirmed that via a schematic).

I removed the bulbs for these little lights on both the oil press. guage and high coolant temp. guage and replaced them with extra bright, red, blinking LED's. I extended the LED's right up to the little lenses so they are really bright and attention-getting. You really notice the blinking LED's on my guages much better than if they were on steady.
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You may be right about the other sender behind the oil filter being used for the RH radiator fan. Seems odd though that one coolant radiator fan would be triggered by a simple switch screwed into the radiator and the other coolant radiator fan controlled by a temp. sender via the Motronic. Looking at the workshop manual doesn't make it seem very straightforward to me. The manual says the RH fan on the oil radiator "is controlled by Motronic computer pack of the r.h. main bearing."

 

Mine had 40 amps in there when I bought it. I had been wondering if 30 amp slow blow would be better than 40 amp "normal" or 40 amp fast blow. Never did anything with that (left the 40 amps in). There must be some serious current draw when the fan motors start going bad if the IAC cannot compensate the idle speed enough.

By the way, I got the fuses that light up (LED) when they're blown, to put in the passenger footwell fuse block for easy/quick confirmation. Unfortunately these light-up fuses only seem to be available for 30 amp and below (no 40's) :-(

 

Gauge and light do use the same sender. The sender contains both a variable resistor for the gauge and a contact for the light (cf section L37 of the electical diagrams in the WSM). This sender is the one which is toward the front of the engine on the cooling pipe bolted on the heads.
If the light is intermittent, it could be either a bad sender or a short to ground somewhere on the wire to the light.

 

That makes more sense. It did not make sense that the Motronic temp sensor would also be connected to the water temp gauge or light.

 

You really have come up with many, many great ideas, eulk! You're extremely innovative.

If you don't mind, where did you source the LED lights and fuses?

 

Thanks Scott. Must be due to boredom

I think I've had the blinking LED's in my "stock" for a few years. Either that or I got them from SuperBright LED'S http://www.superbrightleds.com/ I've converted almost all my bulbs to LED's using parts from them.

The fuses I found at Kragen or I'm sure Pep Boys or any other of those type places have them. I also bought a complete set of these "fuses" for testing purposes (and to carry in emergencies). They do light up and they're not actually fuses but rather circuit breakers that fit into the fuse block locations. If you're troubleshooting a problem that repeatedly blows fuses it's better to use these so you're not going through tons of fuses (especially the LED type). It's also good to carry this set in case you blow a fuse in the middle of nowhere and don't have spares (assuming the problem "clears itself).

Circuit breaker ATC type "fuses" are often taller so it's not always possible to leave them in a car and have the panel cover still fit. Also, there are the automatic reset type and the manual reset type. I prefer manual.

http://www.escience.ca/hobby/RENDER/0001/2065/3099/11978.html

http://www.wiringproducts.com/contents/en-us/d28.html


I didn't buy the parts from these two places in the links. Just inserted here as they popped up in a search.

PS. here's a "teaser" photograph if you haven't seen it before:
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Thanks so much for taking the time to respond.

Best regards,

Scott