Gain extra benefits by becoming a Supporting Member Click here find out how!
Classic Performance Products Classic Parts
American Auto Wire Classic Industries
Join the Community todayDanchuk Catalog
Hellwig Products IncPerformance Rod & CustomEcklers AutoMotive
Nu-Relics Power Windows
Impala Bob's Bob's Chevy Trucks Bob's Chevelle Parts Bob's Classic Chevy

Ecklers AutoMotive
Username Post: Incorrect Temp reading        (Topic#356140)
chevyguyjim 
Silver Supporting Member
Posts: 12
chevyguyjim
Loc: Overland Park, KS
Reg: 06-25-17
04-24-19 08:43 AM - Post#2764919    

I have recently finished a 65 Impala convertible with a 454 using FiTech and Dakota Digital dash. Engine runs great and DD dash water temp sensor is in the standard place on the head. The FiTech water temp sensor is in the intake manifold. FiTech sensor reads 180 which seems correct but DD sensor in head reads 250 which is incorrect. The people at DD say it is an air pocket, but I don't see that. Any ideas on how to solve the problem?
Thanks!

Jim Graham
1965 Impala Convertible
1969 Corvette
2014 Harley Ultra Classic CVO


 
Ecklers AutoMotive
6T5 
"2nd Year Gold Supporting Member
Posts: 204
6T5
Age: 67
Loc: Asheville, NC
Reg: 07-22-17
04-24-19 02:06 PM - Post#2764935    
    In response to chevyguyjim

For start, after it's warmed up I'd use an IR gun to verify the temps at these two locations to narrow it down maybe to the sensor or the gauge. And yes there can be an air pocket, worth checking fluid level. Hope this helps a little...

...Ed

1965 Impala SS


Edited by 6T5 on 04-24-19 02:06 PM. Reason for edit: No reason given.

 
chevyguyjim 
Silver Supporting Member
Posts: 12
chevyguyjim
Loc: Overland Park, KS
Reg: 06-25-17
04-24-19 04:36 PM - Post#2764953    
    In response to 6T5

Thanks, Ed. I do have an IR gun so Ill give that a shot. That sensor is right on the side of the head, probably in the hottest part of the block. But that is where Chevy put their sensor so it must be an accurate place. I will proceed ahead. Thanks!
Jim


Jim Graham
1965 Impala Convertible
1969 Corvette
2014 Harley Ultra Classic CVO


 
Bad56Sedan 
"13th Year" Gold Supporting Member
Posts: 1118
Bad56Sedan
Loc: Pasadena, Texas
Reg: 04-29-04
04-24-19 04:49 PM - Post#2764955    
    In response to chevyguyjim

The air bubble is under the thermostat,
Pull the thermostat and reconnect the fitting, run until warmed up,
Replace thermostat when it cools off.
The thermostat with not open because the air under it has not gotten up to opening temp, yet you see a high temp on the head.
I waited until I saw 230 on the heads, I had thermometers in both heads, I finally noticed with the rad cap off no water movement.
Drilled two 1/8" bypass holes in the thermostat.
I cured it before it got costly.

VC56S 2 door Sedan, 39 Years



 
chevyguyjim 
Silver Supporting Member
Posts: 12
chevyguyjim
Loc: Overland Park, KS
Reg: 06-25-17
04-24-19 07:53 PM - Post#2764967    
    In response to Bad56Sedan

That sounds very interesting, and makes good sense. I'm going to give that a shot......I'll use the IR gun to look over the temps first, and then after. I appreciate the tip and I'll report back in a few days!



Jim Graham
1965 Impala Convertible
1969 Corvette
2014 Harley Ultra Classic CVO


 
ragtp66 
Contributor
Posts: 795
ragtp66
Reg: 12-09-07
04-24-19 09:39 PM - Post#2764973    
    In response to chevyguyjim

If you put teflon tape on the threads remove the sender and remove the teflon tape. Retry. The tape interferes with the ability of the sender to properly ground. otherwise try this:

Why isn't my temperature gauge accurate?
Part 1 of 2

The 1st possible problem:

Your temperature sending unit is defective or is the wrong type (wrong resistance/thermistor).

Most likely you, or a previous owner, had installed a generic sending unit. Auto supply stores carry generic sending units that will fit and function in your engine,. But because these sending units cover a broad range of years/makes/models, they do not have the same precision resistance rating as the factory sending unit specifically designed for your year/make/model car.

These generic replacement sending units may either work, or may give inaccurate readings. It would now be up to you to determine if your gauge displays an accurate reading.

We can solve your first problem. Lectric Limited offers accurate replacement Temperature Sending Units that will perform as-original. These sending units will make your temperature gauge read accurately (provided you have resolved the following problems).

The 2nd possible problem:

If your temperature gauge originally had a resistor bridging the silver post (ground) and the copper post directly across, this resistor may be missing. This is typically a 90 ohm ceramic resistor and must be used.

To the right is a diagram of how a typical temperature gauge should be wired.

If the value of the resistor, on the back of the gauge, bridging the silver post and the copper post directly across, is too high, your gauge will read hotter than the engine's actual temperature. With no resistor (high resistance state) your gauge will peg to the right. (Note: The correlation between resistance and the gauge display is exactly the opposite when adding more resistance in series with the sending unit. If you add more resistance in series with the sending unit, your gauge will display cooler than the engine's actual temperature.)

If the value of that resistor on the back of the gauge is too low, your gauge will read cooler than the engine's actual temperature. With shorted terminals (no resistance state) your gauge will peg to the left. (Note: The correlation between resistance of the sending unit and the gauge display is exactly the opposite. If you could subtract the resistance of the sending unit, your gauge will display hotter than the engine's actual temperature.)

The 3rd possible problem:

You do not have your gauge wired properly. Below is how a typical temperature gauge, with 4 terminals, should be wired. Also shown are 2 ways that you can 'fool' your gauge to display/read cooler. Although we recommend using the correct temperature sending unit, adding an external resistor is an option.

WARNING!!! Jury rigging your car's temperature reporting system to force it to read 'accurately' under normal conditions without first understanding which component(s) of the system are off can be very dangerous. For example, if you 'fix' a temperature gauge with a 50 ohm resistor, when in fact the gauge was operating correctly, could result in your gauge displaying an acceptable 190 degrees (normal driving temp.) when your car is actually operating at a dangerous 260 degrees. Use your discretion.

The 4th possible problem:

Sometimes, in order to correct an inaccurate gauge reading, previous car owners have been known to install a resistor in series with their temperature gauge. Unknown to you, you may have a hidden resistor somewhere between your temperature sending unit and gauge. Additional resistance will cause your gauge to display/read cooler than the actual engine temperature. This resistor needs to be removed in order to give you an accurate gauge reading with our new, accurate sending units. NOTE: Here is a great article about Water Temperature Gauge Accuracy. Be sure to check it out!

The 5th possible problem:

Did you use Teflon tape or pipe thread sealant on the threads of your sending unit? If you did, try removing it and see if that corrects the problem. Note: If you must use something to keep your sending unit from leaking, you can use pipe thread sealant, but do so sparingly.

Any material between the threads of the sending unit and the car's ground (engine) can result in your gauge working improperly, or not working at all. Without the sending unit being grounded, your temperature gauge will show an approximate 100 degree reading (pegged to the left, cold side, of the gauge) no matter what the engine's temperature. If your sending gauge is making a poor (high-resistance) ground to the engine because of Teflon tape or pipe thread sealant, your gauge will display/read cooler than the actual engine temperature.
Part 2 of 2

IT'S A FACT that the original 1963-65 Corvette (and possibly other GM vehicle's) temperature gauge was not accurate!!!

The gauge displayed a reading that was higher than the actual engine temperature. Consequently, your car may be within standard operating temperature even though your gauge reads hot. Click Here for the actual Technical Service Bulletin (TSB), issued by Chevrolet in November 1965, addressing this flaw.

The internals of the 1963, '64 & '65 temperature gauge were electrically the same.

The '63 was cosmetically similar to the '64, but much different than the '66 gauge. Therefore, replacing a '63 or '64 gauge with a '66 gauge was unacceptable for many owners. However, since the '65 gauge was cosmetically similar to the '66 gauge, the '66 gauge (that functioned properly) was a suitable replacement for the '65 gauge.

We can only assume that this is the reason the TSB does not specifically address the 1963-64 Corvette gauges, even though the gauge flaw applied to those years.

Please note that our replacement temperature sending unit will not correct this factory flaw. To correct the flaw in 1963-66 Corvette gauges, you may need to install a 270 - 330 ohm, 1/4 watt ceramic resistor across the 2 posts. This should supply your gauge with the correct resistance in order to read more accurately.

A resistor may be added to make your 1963-82 (approx.) gauge read cooler, and closer to the actual engine temperature (thus compensating for the gauge flaw). There are 2 options shown:

OPTION #1: Using 330 ohms as a base line (meaning to start with a 330 ohm resistor), the more you decrease the resistance, say from 330 to 270 ohms, the cooler the gauge will display. In effect a 270 ohm resistor will make your gauge read slightly cooler than by using a 330 ohm resistor - with the resistor placed between the 2 posts as shown in the diagram above. We do not have specifications correlating ohms to temperature. You will just have to try different value resistors until your gauge displays the actual engine temperature. CAUTION: Do not install too low a value resistor, or you may short-circuit the posts. NOTE: Do not confuse the resistor of this value and in this location (between the 2 posts on the gauge itself) with the resistor mentioned in Option #2 (below).
OPTION #2: On any gauge, you can add a resistor at some point between your temperature sending unit and your gauge. The higher the resistor value, the cooler your gauge will display. We do not have specifications correlating ohms to temperature. You will just have to try different value resistors until your gauge displays the actual engine temperature. A suggestion is to start with a 5 or 10 ohm resistor. Keep adding resistance until you get the desired gauge reading.



Toys:
1958 Impala 2dr Hardtop Under Construction
1966 Chevelle Malibu Convert M20/350 Aztec Bronze
1987 Sea Ray Pachanga 22
2002 Cadillac Escalade EXT Parts chaser
2007 Trailblazer SS -gone and missed


 
62chevy427 
"12th Year" Silver Supporting Member
Posts: 2165
62chevy427
Loc: laurens sc
Reg: 04-13-06
04-25-19 08:45 AM - Post#2765004    
    In response to Bad56Sedan

i always drill a 1/8 hole in a new thermostat before installing it


56 bel air ((since 2002)
62 impala ss (since 1965)
65 el camino (since 1969)
66 nova (since 1987)
67 malibu convertible (since 1981)
72 el camino ss454 (since 1985)
83 gmc 4wd (since 1991)
95 impala (new)
15 chevy equinox



 
A White Sport Coupe 
"9th Year" Silver Supporting Member
Posts: 397
A White Sport Coupe
Reg: 08-19-10
04-25-19 01:13 PM - Post#2765018    
    In response to 62chevy427

Me too. You can drain and refill over and over again without ever restarting the engine. Handy when installing reinstalling parts while stored for the winter.

Bob


 
Texasray 
"3rd Year" Silver Supporting Member
Posts: 89
Texasray
Loc: Texas
Reg: 11-01-16
05-03-19 04:59 PM - Post#2765669    
    In response to A White Sport Coupe

True about the teflon tape.

Reread the OP's original post. He's not using the original sending units or gages.

I would go with trying the hole in the thermostat.

Sam



 
chevyguyjim 
Silver Supporting Member
Posts: 12
chevyguyjim
Loc: Overland Park, KS
Reg: 06-25-17
05-09-19 07:02 PM - Post#2766065    
    In response to Texasray

First I want to thank everyone who made suggestions on my issue. I used an IR heat gun and watched all of the temperatures in them system as the car warmed up. Everything seemed to be just perfect.
I opened up the system and drilled a hole in the thermostat. The sensors are both two-wire so the Teflon tape issue doesn't apply here. I removed both of the sensors (the FiTech in the intake manifold and the Dak Dig in the head) and put them both in a pyrex cup of hot water. They both read the same, as did the IR gun and my wife's cooking thermometer.
I called DD and they sent me a new sensor that has a 1" extended probe. The original one they sent had a sensor flush with the end of the threaded part of the casing. When screwed in the head I don't think the sensor saw any waterflow. I think it was sensing the actual metal temp of the head itself.
When I make the change I will report again!
Thanks again!

Jim Graham
1965 Impala Convertible
1969 Corvette
2014 Harley Ultra Classic CVO


 
Ecklers AutoMotive
Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

406 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.126 seconds.   Total Queries: 16   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 04:14 PM
Top