The last time I drove my 88 E350 the Engine Temp Light came on. The regular gauge said it was normal temp, as in no different than it normally runs which is about dead center of the gauge. The Radiator is new, replaced by the former owner an is an aftermarket 4 row from Czech republic. It has never run hot. The fan clutch is very stiff and locks up like an Osprey. Right now I have the front of the engine torn down to replace the front crank seal and water pump due to leakage from both. While it is apart would it be a good idea to replace the sending unit/switch for the light?? Of course being a van it's near impossible to work on anything without taking a bazillion things off first so I want to do it all just once, so that being said, what should I do??
I have a new Aftermarket Waterpump and have ordered a Motorcraft Thermostat. Is Ford or IH the only source for the switch?? What is the best way to test the switch?? I have a multimeter but have little experience in it's use. I do plan on adding an aftermarket mechanical temp gauge in the near future just for peace-of-mind sometime in the future but just not now. What are your thoughts???

 

Actually just taking the wire off and then putting it back on might fix the problem.

 

Thanks Dave. I tried that and it did work temporarily but returned. I then let it sit overnight and tried again. It happened for a total of 5 or so times. Coolant was a little low the first time so a 50/50 mix of just cheepo coolant/distilled water was added temporaily due to the work to be done the following week. Fleetguard will be going in again with distilled water and the appropriate SCA's. The connector looks good I just cleaned it. If the switch fails, does it fail open or closed?? While it's apart is there a bench test that can be done??

 

You can get that from advance. I think its like 4 dollars. If you gorund the wire going to it, the light comes on. I would check the switch when the engines cold. Put a test light ground clip on + bat terminal and touch to the switch. If lights up, its grounded internally therefore bad. If not, maybe it is the one thats working and the gauge is not. Maybe you should get the mechanical gauge sooner.

 

Thanks luthrobediesel, I'll try that. I'll also see if I can test the other sender, but that may prove more difficult. I'm also wondering if air intrusion may have caused this but the coolant wasn't really that low and I ran with the heater on and off in an attempt to purge any air trapped in the system. It shouldn't as my driveway is fairly steep which makes the radiator cap the highest point of the system. Also wondering if the thermostat may have issues. Gonna replace that with a Motorcraft unit anyways. We have alot of hills here and I made sure to go up down and sideways under full throttle/half throttle and no throttle but still the same. I've been following all the stories on cooling issues lately and wow!!! I'm a little nervous as to what I'll find. I'll be finishing the other work over the next few days and see if I can find a cheap temporary mechanical temp gauge, but what i REALLY want is to build a custom dash using these:
http://www.westach.com/

They are a little $pendy and the site is a little difficult to navigate, but those dual gauges just make my eyes bleed with envy. Still trying to find out if they make Mechanical Water Temp though. Haven't found it yet. Thanks to all on FTE for all the info and help.