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Thread: 3.0L oil and coolant temperature senders for the instrument cluster gauges/lights?

  1. #1
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    3.0L oil and coolant temperature senders for the instrument cluster gauges/lights?

    I have a couple of question about the 3.0L oil and coolant temperature senders that drive the instrument cluster gauges and lights. I'm working on hooking my new harness up in the engine bay, but I'm not quite sure what to make of these senders.

    First, the coolant temperature sensor at the water pump is fine -- that easily hooked up on the harness for MegaSquirt, so no problem there.

    The coolant temperature sender for the temperature gauge in the instrument cluster is the one I'm curious about. This is located on the cylinder head near the throttle near firewall. My harness from Josh (thanks again, Josh!) has a simple ring-style connector, but the sender appears to have two blade-style connections that are clearly meant for a plug (I think a Bosch-style connector, like the 2.8L CPR used?). I'm wondering if I can just attach one of the pins to ground and the other to the sender wire, on the sender operates like a resistor like the other ones do. I presume the 2.8L one was grounded to the engine, since it only had one wire.

    Next, the oil senders. I had expected DeLorean-style senders were present on the passenger and driver's sides, but that doesn't appear to be the case. Instead, I found this:
    - On the passenger side I have a large brass plug next to the oil filter instead of a sender. This is where I realized I should have done more research before now; for the most part I've been figuring out each step as I go along so that I don't get overwhelmed, and it's been working so far...
    - On the driver side, there is what I think is the oil pressure sender near the main pulley end of the engine. Page 40 figure 100 of the 3.0L Engine Overhaul manual suggests that t's the oil pressure sender anyway. It seems to have only one (slightly bent) pin, and the docs say it acts as a variable resistor, so that seems like it should work. I'm just not sure what kind of connector it has, so I'm not sure what to get for my harness.
    - On the driver side near the bottom of the engine is another sender with a two pin Bosch-style connector. I think this is the knock sensor, given the diagram in the Volvo Service Manual page 9-17 figure 13.
    - Figure 13 also references an oil sender switch connector, but I don't actually see where the sender itself is when looking under the car, but I may just not be looking back far enough.

    Also, it looks like I'll need a source for Bosch-style connectors, and whatever kind of connector is on the other sender.

    I guess I could put the 2.8L senders in the 3.0L engine (I think I have them around somewhere...), assuming they fit, but it seems like the existing senders would probably be usable as-is... right?

    I also realize that all of these particular senders are "optional", in that they just drive the instrument cluster, and aren't required for the operation of the vehicle. However, it seems like with a newly-installed engine, I'll want all the sensors I can get to make sure I didn't screw anything up.

    Pictures attached. Thanks!
    Attached Images

  2. #2
    Senior Member AdmiralSenn's Avatar
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    Quote Originally Posted by jangell View Post
    I have a couple of question about the 3.0L oil and coolant temperature senders that drive the instrument cluster gauges and lights. I'm working on hooking my new harness up in the engine bay, but I'm not quite sure what to make of these senders.

    First, the coolant temperature sensor at the water pump is fine -- that easily hooked up on the harness for MegaSquirt, so no problem there.

    The coolant temperature sender for the temperature gauge in the instrument cluster is the one I'm curious about. This is located on the cylinder head near the throttle near firewall. My harness from Josh (thanks again, Josh!) has a simple ring-style connector, but the sender appears to have two blade-style connections that are clearly meant for a plug (I think a Bosch-style connector, like the 2.8L CPR used?). I'm wondering if I can just attach one of the pins to ground and the other to the sender wire, on the sender operates like a resistor like the other ones do. I presume the 2.8L one was grounded to the engine, since it only had one wire.

    You've got it right. I ran a wire back to the 'sensor ground' common pin on the MS unit and connected the CLT lead to the single ring on the coolant sensor. Worked beautifully.



    Not sure on the oil sensors, unfortunately, but I want to say that the later PRVs used one sensor for both the gauge and the warning light. Not sure how accurate that is, maybe one of the 3.0 swap guys can correct that?
    Aka Adam S, aka Adam Wright
    1981 DMC-12 #3416, mothballed in preparation for motor swap
    2006 Volvo S60R

  3. #3
    Senior Member Josh's Avatar
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    I tried getting the coolant temp sender working with the eagle sensor and it was a no go. I did as AdmiralSenn explained and still nothing. So I just unscrewed it and replaced it with the stock delorean sensor. Thus the ring terminal.

    There are two oil senders on the 2.8. One runs the gauge (on the passenger side next to the filter) and the other runs the "oh shit" light as I like to call it. If the oil pressure is too high it will go off. I never hooked up this sender.
    I did hook up the gauge though, and once again I used the delorean sensor. I took the plug out from beside the oil filter in the block, and drilled and tapped a 1/8" NPT hole. Then screwed the oil sender in.

  4. #4
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    Thanks guys.

    The coolant temp gauge sender is hard to get to with everything else mounted around it, or else I would have already pulled it out and and bench tested it. Still, I suppose I really should. I can put the 2.8L temp sensor in, if I still have it, anyway.

    I think the original 2.8L sender grounded to the engine, so it seems like it just needs any ground. Although the MS ground would be cleaner, I expect for a gauge like this it's not as critical. If I don't get to it, I can just read the temp from the water pump temp sensor through MegaSquirt on a laptop screen for a bit, until I get around to doing my custom instrument cluster stuff (you know, after the car is actually running, and then after I replace the A/C system...). I'm guessing a heat gun probably wouldn't get the head anywhere near hot enough to make the sensor register an appreciable of heat while it's still installed in the car, although I guess I could give the a shot, too.

    As for the oil sender, I was going to remove that this morning so that I could hook it up to a multimeter and test it, but the nut seems to have 10 faces, and I was afraid I'd round it with any wrenches I have. Googling suggests I need a special socket for it, so I'll see if I can find that next weekend (depending on the snow storm).

    As for the warning light, I'm guessing you meant that it is there to you when the pressure was too low, right? I admit that I had wondered why there's both a pressure sender and a warning light sender. Maybe it was electrically or mechanically simpler, or for redundancy, or because the light one gave a more absolute reading than the pressure one or something.

    Anyway, I'm definitely more interested in the pressure sender than the warning light sender, although I admit I'm going to have to look through the manual to figure out what the actual pressure range is supposed to be so that I can make sure its working properly.

    Thanks again!

    -- Joe

  5. #5
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    So I got a 1 1/6" oil sender socket, and after whining about not wanting to remove the coolant temperature gauge sender I just went ahead and pulled that too. Here are the results:

    Coolant Temperature Gauge Sender

    I can't figure out how to make the coolant temp sender do anything. I put it in a vice, hooked up an ohm meter to the pins, and hit it with a heat gun. My first clue should have been that the ohm meter reported infinite resistance, which implies that the pins aren't connected, but the heat gun showed the same thing as well -- no change at all.

    I tested an old DeLorean sender, and it worked perfectly fine -- resistance dropped as the temperature increased, as expected, and then decreased as the sender cooled down. As Josh said, the threads are the same so I'm just going to screw that one back into the head and call it a day.

    Oil Pressure Sender

    I mounted the sender in a vice and connected a multimeter to is pins. It took me a bit to figure out how to trip it; I don't have a working air compressor to blow air into the hole on the end. My solution was a pump-action Super Soaker with no water in it, which I'd previously used to clean out a mix of oil and coolant from the engine's coolant passages. It made a nice seal over the end sender.

    This is clearly a switch. With no pressure there is continuity, but once you reach some threshold the switch opens and continuity is lost. As such, it can only run the idiot light, not the pressure gauge.

    While it's a standard design, and there clearly is space for two more pins, Googling suggests that the extra two pins found on some senders are there to shut down the fuel pump if the oil pressure gets too low. This probably means there isn't a sender that does both the switch and gauge functions.

    The 2.8L pressure switch has the same threads, but that's just the idiot light again. The 2.8L pressure gauge sender thread is of course much smaller, so it would need an adaptor (assuming it can operate properly from that location), or to tap a hole in the brass plug like Josh did. Since I can't seem to find an M17 to M10 (I think those are the sizes, anyway; this is the first time I've tried to use calipers to gauge bolt diameters) adaptor, it's looking like I'm going to be tapping the brass plug.

    it's worth noting that there is an actual oil pressure gauge on the Monaco/Premier dashboard, and the manual specifically references it as a variable resistor, so a pressure sensor must be here somewhere. I just have no idea where. It's more confusing because the manual shows separate schematics for the gauge and the light, but calls both senders the "oil pressure sender/switch".

    I have one more theory: Maybe the sender is a single-wire variable resistor grounded to the engine, but at the end of its range (i.e.: low pressure), the wiper falls off the end and opens the contact, turning it into a switch. A pull-down resistor at the idiot light could then be completing the connection to ground to turn on the light, and the gauge would read zero. Or something like that. It seems overly complicated, though, and it wouldn't be possible to tie it into the DMC's stock instrument cluster anyway. I forgot my Super Soaker at the garage, so I don't have a way to deliver a reasonable amount of pressure to the sender to test this theory tonight, so a proper debunking will have to wait.

    ... except that this would make it high pressure switch, not a low pressure switch -- applying too much pressure is what opens the switch. I should also mention that this behavior would also conflict with the service manual, which states that the switch is closed with low oil pressure (Premier/Monaco Service Manual, page 8E-.

    So I'm back to having no idea where a pressure reading is coming from.


    New theory: The thing I thought was a knock sensor might actually be the pressure sensor. I forgot the Monaco had two engines, an inline 4 and the PRV6. It's possible that only the 4 cylinder engine has the knock sensor. I'll pull that one out next time I go to the garage (maybe in the morning, after the snowstorm clears).

    -- Joe
    Last edited by jangell; 01-23-2016 at 08:04 PM.

  6. #6
    EFI'd Member dn010's Avatar
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    I'm running the B280F Volvo EFI engine. I used the original coolant sensor to that engine (2 pin) with the Bosch connector, one wire to MS CLT in and the other to sensor ground, no issues. I think I used the sensor in the cylinder head for the ECU and the one on the pump for the dash gauge.

    The engine also has the single oil sensor on the driver side below the cylinder head - I connected both the oil light and the pressure gauge to it and have had no issues, light is on prior to engine start and off with pressure while running.

    I could be wrong but the sensor in the side of the block does not look like a knock sensor. It looks like it may be a coolant sensor.
    Last edited by dn010; 01-25-2016 at 09:21 AM.
    -----Dan B.

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    I got the mystery sensor off, and the only thing I'm sure about is that it's not an oil pressures sender. It may be a coolant sensor like dn010 says -- the screwed in end is simply flat, but I can't get continuity on it with a multimeter, so I can't actually test it for changing resistance with a heat gun. I don't actually know what a knock sensor looks like, as the manual has no pictures and I can't find anything similar looking on Google. The hole tapped into the block doesn't actually through the engine wall, just into the engine wall. As such, the end of the screw is clean with no oil or anything on it. It seems odd that a temp sensor wouldn't be in the oil or coolant, but maybe it just measures the block temperature?

    So back to the oil pressure switch, I got my Super Soaker, hooked up an ohm meter, and found that the resistance does indeed change as the pressure increases up until the point where it becomes an open switch. I think it works like this:
    - At low pressure there isn't much resistance, so the oil light will be on.
    - As pressure increases, the resistance increases and the light turns off, and the gauge indicates the current presure.
    - If the pressure gets too high, the switch opens. This could turn on the oil light again via a pull-down resistor, and the infinite resistance would cause the gauge to max (or drop to 0 due to the open circuit; I know enough electronics to get by and play with Arduinos, mostly, so I'm fuzzier on this one. It probably depends on how the gauge is set up).

    I'm not sure what the pressure range of the sender is, as I don't have a way to put a pressure gauge on my Super Soaker. I ordered a simple 45 PSI pressure/vacuum kit that I can use to test it, though; would be here in a few days. Mostly i'm curious at this point. This whole thing would have been a lot easier if manufacturers would publish specs for their parts, instead of just saying "this part is for this car", but I guess that's a fringe case from their point of view.

    Thanks for the info dn010 -- it sounds like the way you have it hooked up matches what I've been seeing in my tests. I'll give it a go, although I have to put my electrical system back together before I can test it.

    -- Joe

  8. #8
    EFI'd Member dn010's Avatar
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    If it is just a threaded, dry & flat end then I stand corrected and it would be a knock sensor.
    -----Dan B.

  9. #9
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    Quote Originally Posted by dn010 View Post
    If it is just a threaded, dry & flat end then I stand corrected and it would be a knock sensor.
    That's exactly what it is. Here are some pictures, if you're curious, including the hole that the sensor came out of. The casing was a bit broken on mine, so I was able to pull it off and look at the inside, too.

    Thanks again!

    -- Joe

    IMG_1325.jpg IMG_1287.jpg IMG_1326.jpg

  10. #10
    EFI'd Member dn010's Avatar
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    Yeah, that is one, must have been too early for me - I shouldn't type anything before 11AM or after 11PM!

    Do you plan to replace it and use a knock sensor with your ECU?
    -----Dan B.

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