guitarman376

So, for a long time the TSU (temperature sending unit) wasn't working on my 1969 mustang (351w). The TSU is the heat sensor that sits on top of the engine to measure the temperature of the engine. I went ahead and bought a replacement, and the guage popped to life right away. Now the problem is that the needle goes nearly to the second line from the RIGHT. It never seems to go in the "H" area for Hot, but it is rather disconcerting seeing the needle get close on hot days.The thing that keeps me sane is that I just replaced the thermostat with one that has a cooler-than-stock temperature. I also monitored that the thermostat opens when the needle gets to the area described above. So basically I am worried about whether or not the engine is running at the proper temperature, and trying to figure out how to make the gauge accurate. For you guys with 351w in 69's, shouldn't the needle be in the middle? The only other thing I can think of is that it might be some sort of electrical current problem or something to that effect. Anyone know what's up? Thanks

Stepman

I really don't get the problem.....

Stepman

On the realistic side.....is it pinging? Mine runs right in the middle unless, I sit in traffic too long. It sounds like you may have a flow issue. Put a 180 therm in it it...How big is your radiator?

guitarman376

The problem is that I am not sure whether or not the engine is running hot. It has a 150 thermostat in it I believe (it is definitely cooler than stock temperature). The radiator is 26" I believe, I know the fan is 20". It is the same size as OE.

Gun Jam

you dont want to run a 150 thermo that's for damn sure.

if the car overheats with a good 180 thermostat (recommended) its going to over heat with a 150. The thermo doesnt cool the water it just says when to let the cool water in. Hell the 150 might even make it worse as it would probably never close off allowing water to rush pass the radiator so fast that it already back in the engine before it got a chance to cool off much...

Your best bet is to put the 180 thermostat back in and barrow or buy a non contact thermal temp gun. they instantly read temps so you can tell if its the gauge or not.
http://www.amazon.com/Raytek-Non-Con.../dp/B0002198GY

good luck

-Gun

JoeMustang

I am in the same boat. All my other gauges are working properly, but my temp gauge started showing to the hot side this summer, so I replaced the sending unit. My 68 302 is running very well with no pinging, but the needle on the temp gauge will eventually get all the way up to the H. I have verified the actual running temps with a Fluke digi thermo and it says I am running about 185-190 degrees. I agree with Gun Jam, get something to put your mind at rest as far as ruining anything. I have not received an answer on wether or not you can adjust the reading on a stock gauge, so I may just install a gauge for piece of mind.

guitarman376

Does anyone know where i can find a cheap temperature gun?

Stepman

Well, Ii would but, I left the book at work. Maybe "northern tools". I think that's the name of it.

bodyputtyless

You are correct in your concern. The trouble isn't in your cars cooling system. The trouble is the sensor you installed. I have had this happen to me before. You go to an auto parts store and tell them you need a temperature sensor for a 1969 351 W. They go in the back and sell you what they have. You take it home and install it. You might have even noticed that the new sensor seems a little larger then the original (if you had the original) .But you figure its just the updated sensor. You turn on the car and the temperature readins are high. You start to freak! Here's the remedy. Either go to a Ford dealership parts center, or go to one of the classic Mustang part suppliers and get the exact replacement sensor for your year and engine. Problem will be eliminated. It's simply a case of being given the incorrect sensor for your particular application. The same thing happens when you try to by a filter for an FMX tranny. The key there is you need to know how many bolts hold the pan to the tranny. If not the part store will sell you a filter that fits, but a gasket that won't work. You need to get the exact part for your car. I have a 70 Mach 1. I went through the temperature sensor thing many, many moons ago.

guitarman376

I can tell you know what you're talking about because thats exactly what i did. The funny thing is, I DID notice that the new one is slightly slightly bigger, but I ordered it from Mustangs Plus (I think) but it definitely it said it was specifically for 1969 mustangs with 351w. I am 90% sure that you are correct about the reading being wrong though.