25 replies to this topic

[Earwax]

I am not advocating for moving away from cooling just yet, as I think the condition of the cooling fins, the hoses not collapsing, the coolant itself and radiator clean /flush could all produce results, but before looking for fuel and carb I would plot the dizzy curve. Even with vac advance some curves are too slow/retarded near the 2000- 3000 rpm - which again could contribute to heat. 

[mbolt998]

Update: the car kept getting a bit hot (up to nearly H, but not boiling over) in normal driving. So I just kept driving it because what was I supposed to do. And now (after maybe 3000 miles) it's fine! Goes a tiny bit above N when working hard but that's it. My best theory is just that it was still a bit furred up in there somewhere after 25y off the road.

[JVA10L]

My temperature gauge has started reading hot so a quick search brought me to this thread. The needle used to sit right on N but is now going almost to the H. The thermostat is 82C and when I measure the engine temp with an infrared reader it shows 82C. The sender and the stabiliser are about 50 years old so I replaced the GTR101 but it made no difference so I replaced the stabiliser C34770A and still no different. I am confident the engine is running at 82C because any time I measure the temp by pointing the laser on the infrared reader at the GTR101 it reads 82C, or very near to 82C. Can the gauge be re-calibrated?

[Spider]

My temperature gauge has started reading hot so a quick search brought me to this thread. The needle used to sit right on N but is now going almost to the H. The thermostat is 82C and when I measure the engine temp with an infrared reader it shows 82C. The sender and the stabiliser are about 50 years old so I replaced the GTR101 but it made no difference so I replaced the stabiliser C34770A and still no different. I am confident the engine is running at 82C because any time I measure the temp by pointing the laser on the infrared reader at the GTR101 it reads 82C, or very near to 82C. Can the gauge be re-calibrated?

 

There is some limited adjustment on the gauge but I'd suggest spending a few minutes doing a some basic checks.

Measure the cold resistance of the sender, then get the engine up to normal running temps and measure again. Compare these to the chart on the previous page.

 

Having suggested that, I'm inclined to think that one of the metal strips of the bi-metal strip has cracked. That's not a given, there could also be a wiring fault.

[JVA10L]

 

My temperature gauge has started reading hot so a quick search brought me to this thread. The needle used to sit right on N but is now going almost to the H. The thermostat is 82C and when I measure the engine temp with an infrared reader it shows 82C. The sender and the stabiliser are about 50 years old so I replaced the GTR101 but it made no difference so I replaced the stabiliser C34770A and still no different. I am confident the engine is running at 82C because any time I measure the temp by pointing the laser on the infrared reader at the GTR101 it reads 82C, or very near to 82C. Can the gauge be re-calibrated?

 

There is some limited adjustment on the gauge but I'd suggest spending a few minutes doing a some basic checks.

Measure the cold resistance of the sender, then get the engine up to normal running temps and measure again. Compare these to the chart on the previous page.

 

Having suggested that, I'm inclined to think that one of the metal strips of the bi-metal strip has cracked. That's not a given, there could also be a wiring fault.

 

 

Thanks Spider, I will try the resistance check but as the gauge is also about 50 years old I suspect the problem lies there. It shows exactly the same reading with the brand new sender and stabiliser as it did with the original 50 year old ones. Looks like I need to take the gauge out for a look inside. 

[mbolt998]

 

Thanks Spider, I will try the resistance check but as the gauge is also about 50 years old I suspect the problem lies there. It shows exactly the same reading with the brand new sender and stabiliser as it did with the original 50 year old ones. Looks like I need to take the gauge out for a look inside. 

 

I calibrated everything, including dipping the sensor in hot cooking oil to check the resistance at higher temperatures, and also hooking a variable resistor up to the gauge in the car. My car is only 45 years old but everything was absolutely spot-on. Remarkable. Yes in your case agree it does sound like the gauge though, but better to make sure.

[Spider]

I mentioned above there is some adjustment at the gauge. While it's there, it is only a limited adjustment.

 

If you look on the back of the gauge

 

 

You'll see 2 cork or rubber bungs. These access the adjusters, they are not a screw adjuster, but a slide, they only move through a few degrees. One adjust the Cold end of the scale, the other does the Hot end, but adjusting one end does put the other end out slightly, so you need some patience when doing adjustments, it's back and forth a bit, but you should be able to get there.

The adjusters are only for small tolerances in the manufacture of the components, they can't re-calibrate for a mis-match between gauge and sender or being supplied at a different voltage.

[JVA10L]

 gauge1.jpg   40.82K   1 downloads

 

Thanks for the suggestions. I've been away on holiday and when I got back I opened up the gauge for a look inside. It is a bit corroded on the terminals and the tiny wire carrying the current round the bimetallic strip is starting to unravel. Ordered a new gauge which is now fitted. Not had a chance to test it yet but hopefully problem solved.

 

Thanks again for your help,

 

Chris.

[JVA10L]

This turned into a bit of a saga. As soon as I powered on the ignition, the needle on the "brand new gauge" moved to the extreme left beyond the ‘C’. I ran up to temperature and the needle remained at the extreme left. I contacted the seller (on ebay) but his reaction was "you must be doing something wrong" so I contacted the manufacturer (Caerbont Automotive) who could tell me from the label that the gauge was manufactured 8 years ago in week 23 of 2017 and that it would not work with the GTR101 sender. All gauges manufactured by them since 1993 had to use the TT6811-01 sender. I pointed out that the TT6811-01 was 1/8NPT thread so they then recommended the TT4806-00 which is 5/8UNF. On their own website the TT4806-00 is "no longer stocked" so I sent the gauge back for a refund. I carefully wound the tiny wire back where it should be and set up a test rig to calibrate the old gauge. With the glass off it is obvious what to do. The needle now sits on "N" when running normally.

[Spider]

I know you're sorted now, but there are 1/8" NPT to 5/8" INF adaptors available. I make my own, as it is the TT6811-01 senders that I use.

[JVA10L]

I know you're sorted now, but there are 1/8" NPT to 5/8" INF adaptors available. I make my own, as it is the TT6811-01 senders that I use.

 

Thanks Spider. If I knew then what I know now I would have bought the TT6811-01 and the thread adapter with the new gauge, but having a new GTR101 and being somewhat peed off with the lack of help from the supplier I decided to try fixing my 50 year old gauge. Very satisfying to see it working properly, and I got my money back for the returned 8 year old brand new gauge.

 

Chris.