Running Hot after temp sending unit installed

[199]

I recently purchased a 1966 Mustang 289 C-code from the US and had it shipped abroad to my country. I drove it a several times on trips of no more than 15mins as the temp sending unit wasn't working and I assumed everything was fine other than the sender. So yesterday I got my sender unit and I went to install it,, I assumed you just had to replace it, I realized as i was opening it the coolest was coming out of the engine bay so I quickly removed the old one and installed the new one. Obviously I lost some coolant from the radiator so I went and bought coolant and topped it up, I followed the "burping" method for the radiator although i haven't lost all the coolant. I started the car and temp gauge started to work, gradually it reached H, I know the car needle has to reach almost half but if it next to the H that means its overheating. Did I changed it the wrong way, Do I have to do it again by flushing the radiator from the drain hole and then removing and reinstalling the temp sending unit again and then fill it up with coolant,

I read that sometimes the thermostat fails and might need replacing,, how hard are they to replace, and were are they located and can u show me pics in the engine bay, you help is gonna be truly appreciated as always.

 

[RatStang]

Remove the sensor briefly, allow any potential trapped air beneath the sensor to come out. Reinstall then try again. If it's still reading high then there's a good chance that, that's just where THAT particualr sending unit puts the gauge needle. To verify, you can remove the radiator cap and run the car to operating temp... check the gauge and check your collant temp a candy thermometer (or whatever you have handy that will read water temp in the 160 - 210 degree range).

If the temp is fine but the gauge reads high then you can either try another sending unit, or replace the gauge. Either of those options depends on you knowing what the ACTUAL coolant temp is as measured by a thermometer.

 

[2+2GT]

I always use the genuine Ford thermostat. It's the correct temp range, and stainless, plus it has an air release valve at the top so you don't have to go nuts getting the air out.

 

[TeamEntity]

so if i'm correct it did not work when you bought it ever? maybe the car was overheating prior to this anyways? and now you know? I doubt its anything serious. but to help yah out the thermostat is on the other side of the upper radiator hose on the engine block. the spring side on the thermostat faces the engine block when you install it and should be that way now when you and if you remove the old one. Once you install the new one, thats after you clean off all the old gasket material or rtv let it dry for a while if your going to use rtv and raise the front end up in the air. That will help to get the radiator up as high as you can to release any of the air pockets that will be in the system. Watch you temps. If it gets past 3/4 on the guage shut it down before you hit The H.

 

[yeloxr7]

You probably have the wrong sender for your application. Maybe it's from a later 302 that has a different range of electrical resistance in the power for the instruments. Also there is a possibility that the sender is a switch for a "TEMP" warning light. Does the needle go to "H" immediately or does it move gradually?

 

[199]

You probably have the wrong sender for your application. Maybe it's from a later 302 that has a different range of electrical resistance in the power for the instruments. Also there is a possibility that the sender is a switch for a "TEMP" warning light. Does the needle go to "H" immediately or does it move gradually?

I ordered it from mustangunlimited and its supposedly made for the specific engine.

No it goes to H gradually.

 

[rsweld]

Run the engine and watch the temp, once the gage gets to halfway feel the radiator, if it is cold the your thermostat is stuck closed causing the engine to run hot.

 

[tx65coupe]

All good points.

Do your other gauges read right? If not it could also be an issue with the ICVR. I prefer to buy or make an electronic one. Its more reliable.

 

[dbfarr]

I have heard and experienced aftermarket temp sending units not having the correct electrical resistance.

I replaced mine, wish I hadn't, and the gauge now registers over halfway at normal running. I know the car is not running this hot, I put a huge aluminum radiator and taurus fan in it. Fact is, I did some checking and the resistance for the aftermarket sending units is slightly higher. The forums I read mentioned that the dealer item does not have this problem, the rub? $50 bucks.

Get a laser heat gun and check the intake manifold next to the sending unit. I know, I know, the things are $100, but you'll know once and for all what the issue is.

BTW w/ a 195 thermostat, the gauge should register less than halfway. Not 3/4 like mine does... godd@%#it!!

 

[199]

All good points.

Do your other gauges read right? If not it could also be an issue with the ICVR. I prefer to buy or make an electronic one. Its more reliable.

Well I assume they do the fuel gauge seem right to me, the oil gauge stay next to the High postion while driving and goes doe to low when idling. Amps also seems fine

 

[D.Hearne]

The only way to know for sure where the temps are is to install a mechanical temp gauge. The factory gauges are notoriously inaccurate. And the thermostat isn't in the engine block, it's in a housing at the front of the intake manifold that the upper hose is connected to. Two bolts in the housing. Remove the upper hose, unscrew those two bolts and pop the housing off . It'll be stuck to the intake so you may have to pop it loose with a rubber hammer or something similar.

 

[199]

So i decided to have another look at my heating issue with the feedback I received.

I got myself a digital thermometer made a simple holder for it - pictured below,

Topped up the coolant

The starting temp of radiator coolant was at 92F with the engine off

I started the engine (cold start) and the coolant temperature rose gradually to 195 which was HOT or the max then I stopped the engine (@ 115F the needle was in the middle)

When I stopped the engine the coolant started to flood and came out of the over flow tube, a lot of coolant came out, pictured bellow and in the video


As I was inspecting the engine bay after the engine was off, I noticed a wire was burnt I believe its from the gauge feed harness does this have anything to do with the heating problem, either way what is that cable for (it was yellow pictured below)

I have a link to a short video that i took, I dont know if it well be helpful for you guys or a waste of ur time?

YouTube - 1966 Mustang 289 Running Hot troubleshooting


after several hours I went back and decided to look for the thermostat, DO i just have to unbolt those bold and replace it and the gasket?

 

[199]

This is the information I got from the 1966 Shop Manual

can some explain the open and full open on Low and High

 

[D.Hearne]

195 degrees is not hot. That's normal operating temperature.

 

[199]

195 degrees is not hot. That's normal operating temperature.

Does that mean my gauge is not working properly?

 

[tx65coupe]

I agree 195 degrees is a good operating temp. I would say the temp gauge is reading high.

 

[D.Hearne]

Does that mean my gauge is not working properly?

If it's reading "hot" @ 195* then, yes, the gauge is wrong. As I stated before, the factory gauges are notoriously inaccurate. This isn't a classic Stang problem either. My 89 Ranger's gauges were way off well before I swapped the V8 into it. They went off base when it was only about 5 years old. Both the oil pressure and temp gauges were off. The oil read nearly zero when it was pushing 70 psi. The temp was always hot when the temps were normal (160-200) Put an aftermarket gauge on it along with the factory gauge and you'll see.

 

[199]

If it's reading "hot" @ 195* then, yes, the gauge is wrong. As I stated before, the factory gauges are notoriously inaccurate. This isn't a classic Stang problem either. My 89 Ranger's gauges were way off well before I swapped the V8 into it. They went off base when it was only about 5 years old. Both the oil pressure and temp gauges were off. The oil read nearly zero when it was pushing 70 psi. The temp was always hot when the temps were normal (160-200) Put an aftermarket gauge on it along with the factory gauge and you'll see.

Im really new with working on cars, It would be really helpful if u can direct me to aftermarket gauge and sender etc... and how i would go about installing it (as in having the original and aftermarket), Im looking for something affordable if you can find it from mustangunlimited maybe sunpro as they are affordable that's were I order my parts, if not I dont mind other locations or brands.


by the way will a Motorcraft RT351 Thermostat work on my car as thats what I found in the dealership her in my country, i believe its a 190. I dont mind ordering it online and waiting a week til it get over to me. Will the 190 have any benefits

 

[D.Hearne]

Just order a temp gauge of your choice from Mustangs Unlimited. I prefer to use mechanical gauges, you may prefer electical, but get one that actually reads the temperature, not just Hot or Cold. If your intake doesn't have two ports in the intake for the temp gauge sender, then use brass or stainless pipe fittings and install a "T" fitting in the intake to use both gauges. As for that RT351 thermostat, I'm not sure about. As I recall the thermostats for the 351 Clevelands don't work in other Fords,( if that's what it is.) Someone else may chime in if they know for sure.

 

[Loup-garou]

I'd do as suggested and install an aftermarket temp gauge while keeping the original operating. Once you confirm that the engine is running in its correct temperature range, you might be able to calibrate the factory gauge - see the link for more details. Note also that the original poster in that thread mentioned another discussion of gauge calibration at that site; you might want to sign up there and do a search. You might find a thread on this issue here as well. I know that many years ago, Mustang Monthly magazine ran an article about calibration. It might be in their archives; try their website.

Ford gauge calibration - Ford Mustang Forums