1984 F150, 302/AOD
I've owned this truck for about 10 months now, it just turned 100,000 original miles. Within that time, it has a new radiator, and cap, 180 thermostat, and new hoses, and coolant.Since I've owned it, the factory gauge shows it running hot, even though it appears that it's not. It always runs on the "L" in normal, or higher.
A mechanic friend told me the factory gauges usually give up and read wacky after a while. So I bought some aftermarket gauges, and installed them this last weekend. How I installed the temp gauge was to get a small pipe nipple, and a "T' fitting, screwed both into the hole in the manifold, and ran the factory sender in one hole, the aftermarket sender in the other.
Now the factory gauge barely get's into the normal range, and the aftermarket, when it registers, might show 160. I tried bleeding the air out of the setup a few times, didn't help.
Is there another place I can put the aftermarket sender, and put the stock one back in the manifold hole?

 

A couple of thoughts, maytag906...


My truck has a 4.9L six, so my experience is with it, but I believe a 194/195F thermostat was original for your truck. The engine will be more efficient at that temperature and your heater will work better this winter.


Did you use Teflon tape or sealer on the threads when you installed the "T" fitting? If so, the sending unit is not able to effectively ground, which is necessary for the gauge to function properly.


When the factory temperature gauge is reading high, what about the gas gauge and the oil pressure gauge? If they, too, read high, the ICVR likely is going out.


To check the accuracy of the factory gauge, when up to operating condition have someone who has an I.R. thermometer [hand held] to "shoot" the thermostat housing and radiator.


My 1986 4.9L was computer controlled and had a 2nd temperature sending unit in the thermostat housing. That is no longer being used and would offer a 2nd place that one could place an aftermarket sender. If your 302 is not fuel injected, check the thermostat housing.


Good luck!

 

David is right, but there's another problem - you no longer have the temp sensors, plural, in the stream of coolant. So all they are measuring is the heat in the little tee and it will never be accurate. Temp sensors must be in the stream of coolant, although oil pressure senders can be teed.

So you need to find another fitting if you are going to run both, which I think you should do. The one David suggested should be available, but on some small-blocks there was also one on the water pump or the block.

 

Gas gauge and oil pressure work normal. Lack of heat from the heater has never been a problem with this truck, even with a 180!


I was wondering about the sensors not being in the "stream" of coolant. I don't think there is a plug on the thermostat housing, I'll check the water pump. I was also wondering if there was a plug in the head, maybe. The strange thing, the factory sensor is now on top of the "T", and reads wacky, the aftermarket sensor is out the side, and mostly doesn't read at all. I did use Teflon tape thread sealer. If I shut it down, and leave it sit for 10 minutes or so, the aftermarket gauge will show about 190 or so, while the factory gauge will be pegged H, which is what I would expect.

 

That's not strange at all. The aftermarket sensor is finally getting warm as the heat gets to it while sitting, but while moving the air flow keeps it cool.

The fact that the gas gauge and oil pressure work correctly says the ICVR is working. So you may have a bad sender for the factory gauges. If you have some large resistors you can simulate the sender by placing a 10 ohm resistor from the lead to ground and the gauge should go to Hot. And with a 73 ohm resistor the gauge should show Cold.

 

Thanks, if the typhoon we're now experiencing settles down, I'll go out and do some investigating!

 

You can run just the aftermarket sender to test things. But I like having the factory unit working, even if it isn't perfect, as it is much more visible than almost all aftermarket units - especially those put under the dash. I'm placing mine in the "pocket" to the right of the steering column as it is much more visible than below the dash, which is blocked by the shifter and my right leg. So the factory gauges should be fixed as best they can IMO.

 

Gary is right about your new temp probe not in the flow of coolant. That is a must. I don't agree with him on making the factory unit work. Ok, make it work if there is another hole to stick it in, but if you can't find a spot, forget the factory unit, it's not worth the hassle.

 

What is the consensus on putting a "T" into a heater hose, to install the aftermarket sender? I could then put the stock sender back into the manifold. It should be in a stream of coolant there.

 

If you mean to make up a tee with barbs on the ends of the top and the sender in the bottom and sticking into the stream, that should work. However, my guess is that the temp you will be seeing will be a few degrees lower, and maybe many degrees lower, depending on which hose you place it in. If you go ahead of the heater then it'll be down a few degrees. But after the heater it'll be down quite a few degrees and how many will vary depending on whether you have the heater on and how cold the outside temp is since that's what air is going through the heater.

Your water pump or block doesn't have a port like this?

 

Nothing on the water pump. There is a plug on the thermostat housing, that has a sensor with a couple of vacuum lines on it. A quick glance didn't turn up anything on the block.
If I go the heater hose route, does the flow come from the water pump, and back into the manifold, or vice versa?

 

Yes, I think that's the flow direction. But I wouldn't want to swear that's true.

The sensor on the thermostat housing is in use? The lines probably go to the vacuum advance on one side and the carb on the other?

 

One line comes from the carb, and the other goes into the loom somewhere. The vac advance has a line directly from the carb.
I'm going to try the heater hose "T" , using the hose from the pump. A few degrees either way won't matter.

 

The heater hose isn't the greatest place to read the temp of the engine, but it will probably be ok as long as you call it "good" right now, see how the guage reacts, and use that as a baseline for being "normal". That's how the factory gauge works right? Most temperatures are "normal".

 

That's the plan. Before, the factory gauge would always run in the very high normal range, almost to the "H". But you could grab a radiator hose, and it was no where that hot.


Thanks!