Temp guage not reading correct??

-
Originalowner73 340duster

Originalowner73 340duster

Well-Known Member
Joined
Jan 18, 2018
Messages
514
Reaction score
52
Location
New York
Have 72 340 in my car and the temp guage is reading just above low temp and below running range ..but with temp gun motor is running 180 ish and steady no bubbling or issues expept guage ..can it just be messed up and need replacing??.. car was sitting for almost 20 yrs..flushed motor ..new water pump..new alluminum radiator..new intake manifold gasket and hoses..new temp sensor.new heatercore..to tell you what I've done to the cooling system so far..
 
Bad gauge or sensor, possible buildup corrosion where sensor screws into motor.
While I was working on an overheating issue, I added these to verify the temp, both pretty accurate. the one replacing the radiator cap needs to be touching the fluid to work properly.

Radiator dual guages.jpg
 
Last edited:
Did not notice anything about a new thermostat. If it is , is it the correct one ? Even a new thermostat may not be opening at the correct temperature. I believe (IIRC) it should be a 185'.
You can check it by placing it in a pan of water on stove and applying heat. Using a candy thermometer check the temperature at which it begins to open. You may possibly need to use a higher rated thermostat (190') ????
Yote
 
Radiator temp does not equal engine temp. By the time the engine water gets to the radiator the temp will change. You have your external gauge mounted to the radiator which will give u a different reading than the sender mounted to the engine??

treblig
 
Yote said:
Did not notice anything about a new thermostat. If it is , is it the correct one ? Even a new thermostat may not be opening at the correct temperature. I believe (IIRC) it should be a 185'.
You can check it by placing it in a pan of water on stove and applying heat. Using a candy thermometer check the temperature at which it begins to open. You may possibly need to use a higher rated thermostat (190') ????
Yote
Click to expand...
New 180 thermostat..motor running 180 ish constant..
 
Originalowner73 340duster said:
Have 72 340 in my car and the temp guage is reading just above low temp and below running range ..but with temp gun motor is running 180 ish and steady no bubbling or issues expept guage ..can it just be messed up and need replacing??.. car was sitting for almost 20 yrs..flushed motor ..new water pump..new alluminum radiator..new intake manifold gasket and hoses..new temp sensor.new heatercore..to tell you what I've done to the cooling system so far..
Click to expand...
If the temp gun is showing 180-ish then most likely the thermostat is working ok. Only another gauge will reveal weather the existing gauge is the issue.
 
Treblig said:
Radiator temp does not equal engine temp. By the time the engine water gets to the radiator the temp will change. You have your external gauge mounted to the radiator which will give u a different reading than the sender mounted to the engine??

treblig
Click to expand...
Treblig said:
Radiator temp does not equal engine temp. By the time the engine water gets to the radiator the temp will change. You have your external gauge mounted to the radiator which will give u a different reading than the sender mounted to the engine??

treblig
Click to expand...
Using heat gun..temp is lower at radiator than at manifold..
 
My 72 340 also has a 180' thermostat. Gauge w/new sender shows about the same as yours. Temp gun shows mine at 180' also. I am going to replace mine with a 185' or possibly 190' but I don't think the higher one (190') will be needed.
Yote
 
put the gun right on the thermostat housing, right at the hose going to the radiator.
180 deg is fine.
 
GTS Dave said:
If the temp gun is showing 180-ish then most likely the thermostat is working ok. Only another gauge will reveal weather the existing gauge is the issue.
Click to expand...
Thanks.. maybe will replace one day.. until then will keep checking with temp gun and guess reli
GTS Dave said:
put the gun right on the thermostat housing, right at the hose going to the radiator.
Click to expand...
It's 180's the whole time
 
Originalowner73 340duster said:
Using heat gun..temp is lower at radiator than at manifold..
Click to expand...
I always check the engine temp at the water outlet coming out of the engine and even that is not the temp of the water at the heads but it tells you where the engine is (overall). The factory mounted the temp sender on the intake or on the heads depending on the make/model because they wanted to get as close to the actual temp of the motor.

treblig
 
Yote said:
My 72 340 also has a 180' thermostat. Gauge w/new sender shows about the same as yours. Temp gun shows mine at 180' also. I am going to replace mine with a 185' or possibly 190' but I don't think the higher one (190') will be needed.
Yote
Click to expand...
Ok let me know if your guage changes when you do it please.
 
Originalowner73 340duster said:
Using heat gun..temp is lower at radiator than at manifold..
Click to expand...
The temp is supposed to be lower at the radiator!! In fact, if you check the radiator at the bottom where the water has already been cooled it should be 20 degrees (more or less) cooler....that's how it keeps your engine cool.

treblig
 
The one replacing the radiator cap is a Mr Gasket, get at any auto store. Again, the fluid level must touch the probe on it to work correctly.
 
Treblig said:
The temp is supposed to be lower at the radiator!! In fact, if you check the radiator at the bottom where the water has already been cooled it should be 20 degrees (more or less) cooler....that's how it keeps your engine cool.

treblig
Click to expand...
Yes... working as it should
 
Originalowner73 340duster said:
..any way to chk to see if it's guage or sensor??
Click to expand...

Does your fuel guage work
correctly?

If you short the wire at the sender the guage should rise to full hot. Dont leave it there long or you could burn out your gauge (assuming it is a 1 wire sender). The temp guage works just like the fuel guage. Same resistance range etc. 10 ohms = full or full hot. 72 ohms = empty or cold. This will tell you if it is the sender OR the wiring or guage or gauge voltage regulator
 
Dana67Dart said:
Does your fuel guage work
correctly?

If you short the wire at the sender the guage should rise to full hot. Dont leave it there long or you could burn out your gauge (assuming it is a 1 wire sender). The temp guage works just like the fuel guage. Same resistance range etc. 10 ohms = full or full hot. 72 ohms = empty or cold. This will tell you if it is the sender OR the wiring or guage or gauge voltage regulator
Click to expand...
Yes fuel guage is fine..will test sender ..thanks for info!!
 
factory gauge or aftermarket?

factory has a calibration adjustment.

my 73 factory gauge reads between dead cold and low at normal operating temp.

The last 2 aftermarket gauges I've installed (different brands) both read very low.

One reads 155 on my stock 318 the other reads 160 on my mild built 440.
 
Dana67Dart said:
Does your fuel guage work
correctly?

If you short the wire at the sender the guage should rise to full hot. Dont leave it there long or you could burn out your gauge (assuming it is a 1 wire sender). The temp guage works just like the fuel guage. Same resistance range etc. 10 ohms = full or full hot. 72 ohms = empty or cold. This will tell you if it is the sender OR the wiring or guage or gauge voltage regulator
Click to expand...
I was reading this thread and wondering if someone was going to get to this whole resistance deal? I've had the situation where the Gage has to match the sensor. As in both of them have to work on the same resistance scale. Like buying the gauge that matches the sending unit.
 
Make sure the new sending unit is not the one for the idiot light. O'Reilly (sorry Rusty) sold me the wrong one and I went nuts until I figured that out.
 
Originalowner73 340duster said:
so they gave me a shitty sender??
Click to expand...
Looks that way. Check the PN they gave you and see if it is correct for your application. I suspect (rock auto confirms) the same senders are used on a slant 6, 318, 340, and 360 (72 dart) Not to mention a slew of Fords!

One more possibility... You might have a failing ground. When you shorted the sender wire to ground did you short to the engine or to the battery or chassis?
 
You must log in or register to reply here.
-

Back
Top