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Old 04-26-2019, 12:11 PM   #1
84B23F
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Default Temp Gauge Red-Lined

1990-240

Previous OEM block sender was making temp gauge go up/down, so I replaced it with NOS (New Old Stock) OEM block sender.

Now, temp gauge is rock solid at beginning of red area, with top radiator hose being "flaccid."

Previous Swedish owner maintained vehicle....would removing that resistor cause this behavior? I thought about inserting a resistor at sender's terminal, but not sure about what ohm value is required

I installed new thermostat for NA engine, but I plan to install the "turbo" thermostat, which is lower temp.
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Old 04-26-2019, 03:53 PM   #2
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Has the temp faker been deleted? May've failed right when you put the replacement temp sender in the head.
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Old 04-26-2019, 06:06 PM   #3
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Quote:
Originally Posted by John242Ti View Post
Has the temp faker been deleted?
Unknown...I've been throwing about $500.00 in parts at it since getting it in March....bringing it up to my specs.

Thermostat housing had 184F temp with 92C (197F) thermostat- Temp needle adjacent to red block.

Now with 71C (160F) thermostat...temp needle is one needle's width lower from red block.

I'm going to find a resistor, and place it in series...be nice to find graph showing sender's temp ohm. This temp block sensor has been used on many previous Volvos.

Be nice to find a resistor with wires on each end.
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Old 04-26-2019, 09:33 PM   #4
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This graph is for a 740, but apparently I got an earlier temp sender. Just using ballpark arithmetic, when engine was around 184F temp (Temp needle adjacent to red block), Ohm reading would be around 115 ohms if using earlier temp sensor, which would put temp gauge in red zone using chart for second sender.

Just got the wrong temp sensor....shown below



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Old 04-26-2019, 09:45 PM   #5
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Make sure to install the thermostat with the vent at the top, you probably already know that tho. Do you have any other way to look at engine temps? Like an aftermarket gauge, or pyrometer? Just to confirm what is actually happening with engine temps.
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Old 04-26-2019, 09:48 PM   #6
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^ That sender fits all 240's.
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Old 04-26-2019, 10:56 PM   #7
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Quote:
Originally Posted by 2turbotoys View Post
....actually happening with engine temps.
Yes, I used an Infared Temp Gun, and my hand squeezing top radiator hose.

RE: hiperfauto ^ That sender fits all 240's.

740 literature I cited came from Volvo, which suggests they changed temp sending unit. I may pull it out, and ohm spec it...I just did a search on it, 460191, and yes, you are right.

Back to square one....I'm going to pull off a temp sender from one of my redblocks.

thx
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Old 04-26-2019, 10:57 PM   #8
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Quote:
Originally Posted by 2turbotoys View Post
Make sure to install the thermostat with the vent at the top, you probably already know that tho. Do you have any other way to look at engine temps? Like an aftermarket gauge, or pyrometer? Just to confirm what is actually happening with engine temps.
Even a cheap infrared thermometer. Before you put in resistors to correct the gauge, make sure its not actually overheating.
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Old 04-27-2019, 01:06 AM   #9
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Quote:
Originally Posted by NotSoFresh View Post
make sure its not actually overheating.
I'm going to remove thermostat again, and see where vent hole is located.

I used an Infared Temp Gun, and 184F was highest temp...but if an air cavity existed around temp sensor, higher temp would be possible.

As noted, temp was rock solid with both thermostats installed...previous "flipper" installed a thermostat, and temp gauge was up/down on readings. But at no time was top radiator hose full of pressure, but it had heat in its hose...meaning water was passing thru it..
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Old 04-27-2019, 01:38 AM   #10
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If temp gauge is correct, then either thermostat's vent hole is off, or maybe the water pump installed by the "flipper" is a fail.

After I check thermostat's hole, I'm going to park vehicle in an uphill position, with passenger side in a ditch.

Heater works fine, which suggests water pump is working.
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Old 04-27-2019, 01:44 AM   #11
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I still think it's the temperature compensation board.

http://cleanflametrap.com/tempFaker.html

Our old '92 used to randomly peg its temperature gauge. But, I discovered that if I tapped the "VOLVO" on the cluster face, the gauge would go back down. The 700 series cars use a different temperature gauge on 1987 and newer cars, so they need a different sender.
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Old 04-27-2019, 02:17 AM   #12
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Quote:
Originally Posted by John242Ti View Post
I still think it's the temperature compensation board.
I may hook a wire to block sender, and do ohm meter test while driving...if it acts up after checking thermostat's hole, and "bleeding" the air out. This test would evaluate where the issue exists.
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Old 04-27-2019, 10:36 AM   #13
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You could just stick it in a pot of water and take ohm readings as you bring the pot to a boil.
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Old 04-27-2019, 01:03 PM   #14
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Quote:
Originally Posted by rb92673 View Post
You could just stick it in a pot of water...
Marvin Gaye & Tammi Terrell once said "Ain't Nothing Like the Real Thing"

Live vehicle based ohm evaluation is the real thing:-)
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Old 04-27-2019, 03:33 PM   #15
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Can't trust an oild temp compensator board. It's quicker and easier to just remove it and solder in the jumper wire from pin 1 to pin 3. End of stupid board issue. I've had to do this on every 86 and newer 240 I've had because at some point the board starts reporting bad temp readings.
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Old 04-27-2019, 06:44 PM   #16
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Quote:
Originally Posted by dl242gt View Post
Can't trust an oild temp compensator board...just remove it and solder in the jumper wire from pin 1 to pin 3.
Good advice....but I like to know what happened.

Infared temp gun has shown readings reflective of both thermostats installed. For instances, with

71C (160F) thermostat, around 156F at thermostat housing, and with
92C (197F) thermostat, around 184F at thermostat housing.

Block sender shows 71 Ohms, which temp gauge would "see" this ohm reading at about 200F, as based upon the chart I posted above; and red needle is just before red zone block. So, red needle should have been pointed in the middle range since 71 Ohm reading was reflective of OEM thermostat of 92C (197F).

So yes, "Can't trust an old temp compensator board."

thanks...all
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Old 06-07-2019, 10:47 PM   #17
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FWIW - I had an older TV repair person inspect/repair my 1993-245 instrument cluster, which speedo, temp/fuel gauges, and idiot lights did not work. He replaced some capacitors, cleaned up connections, etc., and now its working fine.

I'll see what he can do with my 1990-240 instrument cluster, rather than doing the bypass.
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Old 06-08-2019, 02:53 PM   #18
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Quote:
Originally Posted by 84B23F View Post
Unknown...I've been throwing about $500.00 in parts at it since getting it in March....bringing it up to my specs.

Thermostat housing had 184F temp with 92C (197F) thermostat- Temp needle adjacent to red block.

Now with 71C (160F) thermostat...temp needle is one needle's width lower from red block.

I'm going to find a resistor, and place it in series...be nice to find graph showing sender's temp ohm. This temp block sensor has been used on many previous Volvos.

Be nice to find a resistor with wires on each end.
So I dealt with a high reading gauge after bypassing my temp faker too. I dont know why 240s read all over the place at the same temps, just a crap design if I had to guess. Anyway I parts cannoned the car to get the cooling system up to snuff anyway (WP, rad, stat, etc) and it always read 3/4 up which is annoying.

Fix was a $1 potentiometer so I can put the temp gauge EXACTLY where I want at operating temp. And it still reads linear so no safety issues either.
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Old 06-17-2019, 01:09 PM   #19
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FWIW - An older TV repair person inspected/cleaned/repaired two instrument clusters. On both, he replaced one capacitor, cleaned up connections, and both are now working fine.

1990-240 and 1993-245 instrument clusters
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