XR4Ti Temperature Gauge - The Cause of Low Temperature

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XR4Ti Temperature Gauge - The Cause of Low Temperature

Post by anglin » Sat Feb 10, 2007 1:41 pm

All,

The recent (Feb 07) thread regarding the operation and range of the XR4Ti's stock temperature gauge brought me to the realization that we didn't have a FAQ on this frequently asked question. Now is your chance to share facts and experience with the community on the topic. After the thread dies down it will be moved to the FAQ section to keep this forever. Errors will be edited as necessary.

The stock temperature gauge often reads low in some XR4Tis (typically the early ones). It is not unusual for the gauge to read right at or slightly above the bottom hash mark when at full operating temperature. Apparently, the gauge sender and the gauge didn't have matching ranges. A later gauge sender, often referred to as the "purple ring" temperature sender, usually rectifies the problem.

The purple ring sender:

Image

(Can you guess why it is called "purple ring?")

The gauge sender is in the lower intake manifold. More specifically, it is in the brass tee fitting coming out of the lower intake. (Can someone fact check that sentence. I haven't touched a Merkur in a while and my brain might be failing me.) A single wire connects to it which is held in place by friction and the tension of the electrical connector.

Can anyone help with the hex size of the fitting? I don't have a sender in southwest Asia with me to check it out myself.
DPDISXR4Ti wrote:All fittings are 3/8" NPT. The hex on the sender requires a 5/8" wrench or socket.
Naturally, there is more than one possibility for a gauge that reads low. I've seen lower intakes that were heavily clogged with the copper from radiator leak stopping additives. Complete lack of coolant flow past the gauge sender can extraordinary effects on gauge accuracy (among other problems). As the wiring ages the increased resistence of the wire can also cause gauge accuracy problems.

Replacement is fairly easy and can be done without fiddling with a bunch of stuff. I've found that I can get the old one out and the new one in without having to drain the cooling system. Yes, some coolant flows out of the opening with the gauge sender out of the manifold. If it doesn't leak then you have a clog that needs to be addressed. Don't use teflon tape on the sender. It has a thread sealant on it that allows the sender to maintain its ground with the engine block.

The clogging problem in the lower intake and around the gauge sender is reason to never use the leak stopping additive to the XR4Ti cooling system. It'll clog your heater core too.

My personal preference is to install a quality aftermarket gauge in order to get a numerical value to the coolant temperature, rather than a range that we don't know the actual scale to. This has been done to the racer and will be done to my road car.

That's all I can think of right now. Please post and add your knowledge.
Last edited by anglin on Sat Dec 01, 2007 11:33 am, edited 3 times in total.

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Post by John R. Rowlands » Sun Feb 11, 2007 10:12 am

Chris,

As you so eloquently stated in the "XR4Ti Temperature Gauge - FAQ Peer Review". I'll add my two cents. I have a 85 XR that has the temperature gauge sending unit located on the drivers side in the block under the intake manifold in the back of the engine. In my opinion a far better place for it to be, as there is less likely to be a lot of crud in that area. This brings up the question as to whether this "boss" is available on all XR's?. If memory serves me correctly the sensor takes a 1" socket/wrench.

Stay well in southwest Asia.

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Post by DPDISXR4Ti » Sun Feb 11, 2007 11:37 am

Here's a pic of an original sender in the original T-fitting which screws into the lower intake. Note the white rather than purple ring on the sender.
Image
All fittings are 3/8" NPT. The hex on the sender requires a 5/8" wrench or socket.

I am of the opinion that ALL of the XR's came with the white ring sender. I think the purple ring sender was only a service replacement part.
Brad

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Post by RatFink » Sun Feb 11, 2007 12:35 pm

I noticed a diference in the operation of the gague when I "insulated" my sender with teflon tape.

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Post by jacobrussell » Sun Feb 11, 2007 10:13 pm

you do not want to insulate it AT ALL it is a resistanance gauge right..
so where does it making its ground
the body of the sender -
to the fitting -
to the intake mani
wich is bolted to the block... have you seen our stock grounds?


i would be willing to bet some peoples problems could be fixed by a better ground to the intake mani (ever noticed the one on the rear of the manifold?)

two huge grounds could make a BIG differance on spark and sensors on your engine
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Post by anglin » Mon Feb 12, 2007 1:23 pm

DPDISXR4Ti wrote:Here's a pic of an original sender in the original T-fitting which screws into the lower intake. Note the white rather than purple ring on the sender.
...
I am of the opinion that ALL of the XR's came with the white ring sender. I think the purple ring sender was only a service replacement part.
Thanks for sharing, Brad. I thought it was in that fitting at the intake manifold coolant outlet.

It is interesting that you mention that you believe all XRs came with the white ring sender. When I picked up the Rosso Red 88 in 1997 it had a gauge that was functional in the right range. When the car was totalled I took the motor out and found a purple ring sender in the car, which was what I was expecting. The car must have had the service done.

Was there a TSB related to the temp sender? I seem to recall there was, but it's been a long time since I've even thought about it...
jacobrussell wrote:... some peoples problems could be fixed by a better ground to the intake mani... two huge grounds could make a BIG differance...
Focus, man. Focus. We're building a temp sender FAQ. You're right, just in the wrong place! :D

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Post by turboplz » Mon Feb 12, 2007 10:11 pm

One thing I found when adding a new ported lower manifold was that it didn't have the brass "tee" fitting on it, rather just a nipple coming out that had been corroded on and would not come out by any means of force or coercion. I did the saab 900 radiator swap the same time as the manifold swap so to solve my sensor problem I took out the plug where the saab fan went into the radiator and put the sensor there(sunpro gauge). There's things that I do and don't like about it in this location, for one I don't know exactly when the motor has reached "operating temp" but seeing how it's located on the top of the radiator it will see some of the warmest temps once the thermostat starts to open and close and I will know if I'm getting too warm.

I plan on installing another gauge in the block this weekend and keep the one on the radiator so I can see what kind of a difference there is in the two locations. I'll report back on my findings next week.

Jason
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Post by merk23literturbo » Mon Feb 12, 2007 11:15 pm

My experience: A stock gauge that is bad reads at the very top of the band. It still works but it reads way high.

I have no experience with a good stock sender.

My car had a bad sender(read real high) when I bought it in 1997. I purchased a Purple Ring sender from Ford and the gauge reads just above the lower hash marks in normal driving. If you get stuck in traffic it will slowly go to halfwway and then the engine cooling fan comes on for a little bit and reduces the temp. I also have a real temp gauge in the stock lower intake to verify what the actual temps are when all this is happening.
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Post by richardcurtis » Tue Feb 13, 2007 8:37 am

Like merk23literturbo, I've installed a new purple-ring sensor (after cleaning out the lower intake) AND an aftermarket coolant temp gauge. At normal temps, the stock gauge needle points between 3-4 o'clock on the gauge face (estimated at 3:30 o'clock); at that time the aftermarket gauge reads around 180 after warmed up on a summer day. As the engine heats up (as in idling along in bumper-to-bumper traffic), the aftermarket needle will move toward 210 as the stock gauge starts to move more toward the 3 o'clock position. As the aftermarket needle hits 210, the stock needle is at 3 o'clock and then the radiator fan comes on and cools things back down to 190-192, and then the fan goes off. The stock gauge by then has dropped back to its normal position between 3 and 4 o'clock on the gauge.

If you turn on the a/c fan when the radiator fan kicks on, the coolant will cool more quickly.

On cold days such as we've been experiencing here in N. Virginia lately (30 degrees), the aftermarket needle barely registers 150 degrees after "spirited" and long driving.
Richard Curtis
Fairfax Station, Va. '89XR (gone to a new home but not forgotten)

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Post by DPDISXR4Ti » Tue Feb 13, 2007 10:53 am

richardcurtis wrote:On cold days such as we've been experiencing here in N. Virginia lately (30 degrees), the aftermarket needle barely registers 150 degrees after "spirited" and long driving.
I don't want to get too far off the subject, but that tells me that your thermostat isn't closing completely Richard. In my experience, this is very common. In fact, I've gone through 3 thermostat changes trying to get one that doesn't leak - it's what lead me to the red-neck thermostat approach - cardboard partially blocking the radiator. :roll:

Okay, this does relate back to the gauge sender. Given that the stock white-ring sender reads so low (even once warmed up), a lot of people are running around in cold weather never reaching proper operating temperature of ~192' F. The problem is that the difference in gauge indication between 150 and 192 is barely decipherable.
Brad

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Post by richardcurtis » Tue Feb 13, 2007 12:27 pm

Brad: Hmmm. That's interesting observation. And it's a brand-new thermostat and I checked it before installing (put it in a pot of water and watched the thermometer as the water reached the boiling point). Maybe it was bad, as you point out. However, wehn the weather is warm, the aftermarket gauge reads reads right at 190 most of the time. I'll install a new thermostat just to be sure. Thanks for the heads up.
Richard Curtis
Fairfax Station, Va. '89XR (gone to a new home but not forgotten)

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Post by DPDISXR4Ti » Tue Feb 13, 2007 12:49 pm

Thinking about it some more Richard, my most recent theory was that it was actually the perimeter housing seal that was leaking rather than the thermostat itself. I have another thermostat with a new rubber seal awaiting installation - just haven't bothered to install it since I haven't been driving the car lately.

The other option is that coolant is getting out to the radiator via one of the other smaller hoses. Given the complexity of the hose routing on this car, that's a possibility as well.
Brad

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Temperature sensor

Post by John R. Rowlands » Wed Feb 14, 2007 9:31 am

Brad,

In looking at the picture that you posted, the white part is an insulator. The "ring" between the insulator and the brass body to me looks purple!

John
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Re: Temperature sensor

Post by DPDISXR4Ti » Wed Feb 14, 2007 11:24 am

John R. Rowlands wrote:In looking at the picture that you posted, the white part is an insulator. The "ring" between the insulator and the brass body to me looks purple!
Huh? :? I'm not seeing what you're seeing John. Compare my pic to Anglin's. The part that is white on my original sender is purple on Anglin's.
Brad

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Re: Temperature sensor

Post by John R. Rowlands » Wed Feb 14, 2007 12:04 pm

DPDISXR4Ti wrote:
John R. Rowlands wrote:In looking at the picture that you posted, the white part is an insulator. The "ring" between the insulator and the brass body to me looks purple!
Huh? :? I'm not seeing what you're seeing John. Compare my pic to Anglin's. The part that is white on my original sender is purple on Anglin's.
Did you clean the ring between what I'm calling the insulator and the brass case?

John
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