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I have been installing float switches in Volvo coolant reservoirs as part of low coolant circuits for some time now. A few years ago I purchased a dozen of them. At this point my supply is exhausted.
These old switches were installed in the bottom of the reservoir and as long as there was coolant present the circuit remained open. When the coolant level dropped the float fell and completed the circuit which illuminated a light on the dash.
The only ones I have found would keep the light on until the coolant was low and then the light would go out. In the past removing the clip and turning the float upside down would change it to being normally open rather than normally closed. Unfortunately the ones I have found don’t offer that option- they are normally closed regardless of the float’s orientation. I think I would find the light being on all the time annoying and going out isn’t much of an alert when the coolant gets low.
Does anyone know where I might find float switches that will complete the circuit when the coolant level falls?
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Any twenty minute job is just a broken bolt away from a three day ordeal
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"Does anyone know where I might find float switches that will complete the circuit when the coolant level falls?"
Randy, in 20 minutes I found the four float switches I'd squirreled away in the garage, unused, untried. They are the same as in this current ebay listing:
https://www.ebay.com/itm/142763222556
They mount horizontally from the side and depending on which way you orient the float, they operate closed circuit or open circuit with low liquid level.
Could be you've seen these and dismissed the idea of putting a large hole in the side of your reservoir to mount them. That may even be the reason I left them linger unused.
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Art Benstein near Baltimore
From Rock Auto's December 2021 Newsletter:
I was in college in Colorado in 1976, and my wife and I bought a Mazda 626. Our homes were in NJ, and I decided to add an aftermarket cruise control to the car to help make the long drives back and forth more comfortable. I put in the control unit, solenoid and bellows for the throttle, brake switch, and the pick-up and magnet on the driveshaft. The magnet had to be tapped in position so it would not fly off the shaft at speed. Several weeks after adding the system, a horrible noise developed at 55+ mph. When the car slowed, the noise went away.
It had to be a problem with the transmission. I took it out, tore it down in my apartment, used all the same gaskets to rebuild it and stuffed it back in. The horrible noise still occurred. I was frustrated. My wife (who knows everything) said it was something I did with the cruise control. She was right. I wrapped the tape backwards on the driveshaft and over 55 mph it flew out and hit the exhaust. Under 55 mph centrifugal force was lower, the tape fell back in and the noise was gone. I re-wrapped it in the opposite direction and all was fixed...
Often times people that "know nothing" take a simple approach and figure it out with common sense!
Bill in New Jersey
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Yes, while I was looking for replacement switches I saw those. However, I guess my mind was set on replacement with a similar switch and blew right past them.
Nice that the orientation would solve the normally open/closed problem I encountered.
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Any twenty minute job is just a broken bolt away from a three day ordeal
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Dave,
Thanks for your reply. I actually have one of the new float switches that I described that I got from AliExpress. Your suggestion of using a relay in the circuit sounds promising. I will need tutoring to incorporate it, but I am going to get a relay (again from AliExpress). The one that I plan on ordering is described as “1Pc Car Relay 12V 20A Blue 4Pins Automotive Small Denso Relay” and an image is attached below.
Is there any reason that one shouldn’t work for my application?
Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal
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If you want too try using a typical "changeover" relay (5-pins with a terminal labelled 87a for the normally closed circuit), the pins you would want to use to change the float switch behaviour are as follows:
85(-) .. Energizer coil (ground) ->to the float switch and then to chassis ground
86(+) . Energizer coil (+12V) <-from a nearby KP-II fused power source
87 ..... Load (normally open) -unconnected
87a ... Load (normally closed) <-ungrounded output from the instrument cluster fluid level warning light
30 ..... Load common ->to chassis ground (for the warning light)
Note that in 700/900s the instrument cluster power (typically a blue/red wire on the largest connector) is unfused, so don't be tempted to use that for your 12V source. If you're doing this under the dash, try the cigarette lighter.
For those interested in doing this, the 940 instrument clusters have an unused coolant reservoir level warning light (typically next to the ABS light). 960s had a fluid sensor. There should be an unused 2-pin connector near the reservoir with a violet wire (from the cluster) and black (ground) wire. In 740s, there's a similar unused warning light for the washer bottle level (typically next to the bulb out light). In 700s, and only when present, a 2-pin connector may be found at the washer bottle (typically a black wire plus a red/black wire in 900s or a blue/white wire in 700s), otherwise you have to either try finding these wires at a main connector block under the hood and if not present there then run a wire back up to the open pin on the cluster. The bulbs, when present (with or without the level sensors present), illuminate with all the others when in KP-II without the engine running and when running get their grounds through the fluid level sensors.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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Thanks Dave, but I have to say I am confused. Doesn't the power to the coil have to be interrupted for the path between 30 and 87A to be completed and the warning light to come on?
I posted this image to my last response to Art.
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Any twenty minute job is just a broken bolt away from a three day ordeal
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To repeat my reply above, you've almost got it, just one misundertanding to overcome. 30 needs to be ground. If you check your instrument cluster wiring diagrams carefully, you'll see the dash light is seeking ground, not wanting power. That's also how they can have all the lights illuminate in KP-II when the alternator isn't running.
Edit: Best not to run 12V up to the sensor and back to the relay for ground (that's not how the 960s are wired), do it my way, plus you've got it backwards for some relays that have a diode on the coil. Do you have that open reservoir connector present under the hood? If present, you can do everything up under the dash behind the cluster using my suggestions.
(sorry, multiple edits going on here while thinking and typing on a tiny keypoad)
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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>If you check your instrument cluster wiring diagrams carefully, you'll see the dash light is seeking ground, not wanting power
The cluster on my set up is not involved. The original float switch was supplying power to a lamp I added to the area near the heater controls.
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Any twenty minute job is just a broken bolt away from a three day ordeal
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Ah, a separate light. Then you're correct. I thought you were trying to do it like a 960 using the existing unused coolant fluid level warning light in the 940 clusters. Maybe it was Spook who was into that trick, but I thought it was you. You'd just need a little square twist bulb to do it OEM as I described.
So, yes, here's perhaps a better way to do it your way with the relay up under the dash protected and a separate light there, but only needing to run a single wire up to the fluid level sensor and then to the chassis ground rail by the right headlight (if memory serves correctly):
85(-) .. Energizer coil (ground) ->to the float switch and then to chassis ground (front fender)
86(+) . Energizer coil (+12V) <-from a nearby KP-II fused power source (cigarette lighter)
87 ..... Load (normally open) -unconnected
87a ... Load (normally closed) ->to the warning light and then to chassis ground
30 ..... Load common <- 12V from a a KP-II fused power source, so simply bridged to pin 86(+) (as per Art's original comment)
(87a and 30 can be switched if it makes the bridging easier)
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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I'm incorrect above, the cigarette lighter is on KP-I, not KP-II, so not ideal as the relay would always be drawing a little power in accessory mode when the engine isn't running. A good nearby KP-II fused source would then be tapping into the window/mirror defrost switch, the blue/yellow wire (both 700s and 900s). Ground can be grabbed off the black wire there.
To repeat myself from elsehere in this thread so as to make this branch of the discussion complete for others, I just went out and checked my 940s. Neither wire harness has the unused coolant level connector I mentioned near the reservoir like the 960s. The 700s are likely similar without the connector. However, my 904s do have that unused washer level 2-pin connector down by the bottle with the blue/white wire that I mentioned (other wire is black to ground). That wire goes up to the unused instrument cluster dash warning light. You could sever that wire at the cluster connector and splice in a wire to your relay, saving you having to route any wiring through the firewall. If you can set up a float switch to work normally and not needing a relay, it would make it the same as a 960. You can either sever the blue/white wire there or even try pushing out the pin and moving it over to that unused coolant level warning light I mentioned. All you would then need there would be a square twist lock dash bulb.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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The relay in your picture is likely a relay with only normally open contacts, also known as form A. Look for a form C relay, one with five contacts. Technically form B, with only normally closed contacts is what you're after, but form C, with both is more readily available. Any 5-pin automotive cube relay will do it, and you can likely have it today from an auto parts store in town.
Wire the coil of the relay in series with your normally-closed float switch between ignition-switched battery and ground. Then wire the normally closed contacts of the relay in series with your warning lamp.
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Art Benstein near Baltimore
These jokes should be in Alt.ernating
I'm shocked that you said that, you could use some en-lightning
Where the circuit breaker for this re-volt-ing thread?
We should all have more resistance.
Perhaps if we switched to another topic.
I just thought I'd zap in and relay my disgust at these puns.
The amount of contributions to this thread is AMPle
My sister would enjoy these. I'll contact her and relay them.
I was considering adding to this but I expect too much RESISTANCE.
Yeah, we've just lost the spark in this thread.
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Thank you, Art. I called my local auto supply (not one of the nationally franchised chains). I explained what I was looking for. They were unable to help me because I didn't have a "number" or application for them to reference.
I wonder if that large bag of relays I have from parting out old Volvos would have a usable form B or C relay? Is any cube relay with five pins going to work after I find the normally open and normally closed pins?
Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal
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I'm sure you'll have one that will work, if you've got a box of pullouts from volvos. One with 5 pins. Look at them closely; they should have some kind of legend identifying terminals.
A metal cased Stribel and a plastic Hella found in my box of relays were both numbered the same. The coil is across terminals 85 and 86. The common contact is 30. The pin in the middle, 87a is the normally closed one you're looking for. Pin 87 is the normally open pin you won't use.
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Art Benstein near Baltimore
Can some repost the whole thread? Some of the articles have been
OHMitted.
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Further looking gave me another relay that does in fact identify 87A. I also found diagrams on several others that indicate the relays with two 87's are simply two terminals performing the same function.
So now I am working with Volvo 3 515 647 12V 16A
Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal
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Yes, exactly.
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Art Benstein near Baltimore
What Thomas Edison's Mother might have said to her son:
"Of course I'm proud that you invented the electric light bulb. Now turn it off and get to bed!"
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I came up with a Bosch 12V 30A part#0 332 014 151 I may be able to come up with a proper connector as well.
Pins are identified as 30 85, 86 and two 87's (no 87A designation). I guess I can do a test setup to determine that the middle 87 is in fact the 87A (normally closed)?
You say the coil is "across terminals 85 and 86". What exactly does that mean?
Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal
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That relay might be a dual form A, the rare one used in the headlight circuit. To verify, check continuity between 30 and either of the 87s. If none, then set that relay aside and look for one with 87a and test it the same way. You're looking for continuity between 30 and some other pin as the normally closed contact.
The coil is the load your float switch is going to send power to. Most relays, it won't matter which side, 85 or 86 is the positive side, but some have flyback diodes internal wired across the coil, so the convention is to use the relay with terminal 86 toward the battery +. See the Wikipedia on din 72552, but don't let it stand in your way on the other terminal designation.
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Art Benstein near Baltimore
Q: Do you know how an electrician tells if he's working with AC or DC power?
A: If it's AC, his teeth chatter when he grabs the conductors. If it's DC, they just clamp together.
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Thanks very much, Art. I appreciate you taking the time to walk me through this. Do I need to be concerned with what gauge wire I use to power the relay coil?
The diagram on the relay would indicate that 86 is a 12V feed and 85 is the ground. When I put a meter to it on the bench I have continuity 30 to 87A.
Does this make sense? When power is supplied to 86 (in my case the closed float switch) the coil will open that 30 to 87A path and the dash lamp will not illuminate. If the float switch falls enough to open the float switch the relay coil will lose power causing the dash light to illuminate.
Edit: This is not compatible with Dave's wiring suggestions. I am confused I thought the coil power had to be interrupted to cause the dash lamp to illuminate.
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Any twenty minute job is just a broken bolt away from a three day ordeal
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"Do I need to be concerned with what gauge wire..."
Short answer is yes. Not to make it work, but to ensure a wiring fault later in life will take out the fuse and not start a fire.
Your ohmmeter readings make sense.
Before turning in last night, I thought I'd ask you about how you planned to use these, i.e. an existing light in the instrument cluster, referenced to ground or battery. Dave knows the 940, and gave you the right suggestions I think, but then I see you are providing your own lamp and have all the options.
Given these options, I'd locate the relay as close as practical to the fused ignition switched battery source, and wire terminals 30 and 86 together to it with a short piece of 20AWG automotive wire. 87A then to your lamp and the other side of the lamp to ground. Then, the long wire to the float switch from 85 can get pinched anywhere on its path to the reservoir and merely cause the warning circuit to malfunction rather than have to blow the fuse. The float switch interrupts the circuit on the grounded side. I think that's what Dave was thinking too.
I bought a few float switches years ago. Not sure if I could put my hands on them quickly to check out whether they float open or closed. Your thread gave me renewed interest in the idea, remembering the one and only "catastrophic loss of coolant" incident I experienced with a 240 over 20 years ago. When that happened, I had a turbo pressure gauge tapped into the overflow plumbing in the reservoir.
Not as much pressure in the 240's reservoir as in the 7/9 cars.
But when I saw the wisps of vapor, a glance at the gauge told me it was time to get to the right lane and off the interstate. I'd rather do it the way you're doing it.
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Art Benstein near Baltimore
Sign on on the side of the electrician’s van – “Let Us Get Rid of Your Shorts”.
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I appreciate yours and Dave’s help. It did not occur to me that I should have indicated that I was using a separate light I installed on the dash. The ones I use were from Radio Shack. They are 3/8” diameter and a very bright red. There was no missing that light. When the coolant got low the float would blink the light due to the sloshing of the coolant in the reservoir. When I fitted my son’s 240 with one twenty years ago I threatened to have the float switch control the radio power, because I knew that he would deem a nonfunctioning radio as a true emergency.
Those circuits have saved my bacon three times during our almost forty year history with old Volvos. A ruptured heater hose, a radiator hose and a failed water pump seal were brought to the driver’s attention before overheating occurred.
I can see having the float switch on the ground side (85) makes the most sense and that’s what I will do.
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Any twenty minute job is just a broken bolt away from a three day ordeal
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I just realized I was incorrect and the cigarette lighter is actually on KP-I, not KP-II as I suggested for a power source. A better fused source might be the wire to the window/mirror defrost switch.
You've now got me interested in putting this on my Volvo project list. I just went out and checked my 940s. Neither wire harness has the unused coolant level connector I mentioned near the reservoir like the 960s. The 700s are likely similar without the connector. However, the 900s do have that unused washer level 2-pin connector down by the bottle with the blue/white wire that I mentioned (other wire is black to ground). That wire goes up to the unused instrument cluster dash warning light. You could sever that wire at the cluster connector and splice in a wire to your relay, saving you having to route any wiring through the firewall. If I could set up a float switch to work normally, it would make a nice little project. I'd either sever the wire or push out the pin and simply move it over to that unused coolant level warning light I mentioned. I've already got spare dash bulbs.
I like Art's little float switch that would install through the side of the reservoir. Note that there are vertical supports molded inside the 700/900 reservoirs. You would need to make sure you have internal clearance, also I think drilling through the top the way you do possibly preserves more of the structural integrity of the reservoir walls than the front side. I think the 960 one may install through the bottom where there's a molded stud, so uses a common float switch. Art notes that the 700/900s use the higher pressure green gas cap. One of the first things I did with my turbo after the heater core went and needed to be replaced was switch to a black 240 low pressure rad cap I had on hand. Turbos are a hotter and more hostile environment under the hood and I somehow figured why push my luck with the next heater core. The other car is still the green cap.
Cutting out the radio on your son when the coolant goes low, so funny. You could use the other side of the relay to power the radio to do this, but you'd want to use the radio's KP-I power source otherwise the radio wouldn't work in accessory mode. I'm trying to remember if the 240 instrument clusters have an unused warning light that might be suitable for doing this my original way.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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This set up is on my son’s 92 745. I already have the wire through the firewall to the float switch so I will just use the switch for the ground to the coil. Whenever I need a wire through the firewall I push it through the rubber grommet that accommodates the cruise control vacuum hose. I have always installed the switches on the bottom of the reservoirs. While I realize fuse taps are not the best way to get 12v I always use the protected side of the fuse for the tap and haven’t had any problems.
I maintain four 7/9 series cars (including two turbos) and they all have black reservoir caps. I haven’t had any problems with them running hot. I think the black caps help guard against stressing the cooling systems in our “old” cars.
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Any twenty minute job is just a broken bolt away from a three day ordeal
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(EDIT Randy's diagram is correct if done with a saparate dash warning light, not the existing instrument cluster fluid level warning light that Volvo provides as I had assumed. See replies elsewhere between Randy and me for a better way to do this his way and using less wire.)
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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Hi Randy. I've always thought about doing one of those, but never got around to it. So far, I've trusted myself and my wife to notice the needle going high and me looking under the hood enough. Have you thought about running one of those common float switches to the normally closed side of a relay that runs the dash light? Both sides of the relay should be on KP-II for power. As long as there is coolant the relay will be energized by the float switch and keep the dash light out. It would work, but would normally draw a little power. I see small 75 mm (3" total length, maybe 2-3/8" stem height) white poly float switches similar to yours pictured on Aliexpress at the moment for under $3 counting shipping https://www.aliexpress.com/item/1005004587331649.html?. It's not clear if those float switches are closed at top or bottom of travel, but at that price it might be worth the experiment. Cheap 12V solid state relays that you can solder to and only draw an amp or two can also be found there for a couple of bucks. Used Volvo reservoirs out of a 760/960 from a yard would seem another option.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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