[Query:] On a typical water pump installation, is some kind of sealant, like RTV, needed, or, just the paper gasket? If, RTV is used, where does it go? On the gasket-to-pump, or gasket-to-head?  [Response 1: Chip Hewette ] Only use the paper gasket!  Carefully align the paper gasket using the two studs on the engine block, then apply the pump. Tighten nuts and bolts carefully, snugging them down in a crossing pattern. The pump is aluminum, and you risk a seal failure if you tighten one bolt fully before all the others are nearly tight.  [Response 2:  Dick Riess] Use the paper gasket only AND clean mating surfaces, including the bottom of head mating surface. [Response 3: Don Foster] You ask different people, you get different opinions. I like to use a touch of (red) RTV on the top O-ring and on the heater pipe O-ring. In the past I've used Permatex aircraft gasket cement on the paper gasket -- it works, and I've never had a failure. BUT it's a b*tch to remove next time around.   So I install the gasket dry. Dick's caution about clean mating surfaces is critical, and Chip is absolutely right about tightening carefully and using a cross pattern.   Don't forget to pry the pump up toward the head before tightening -- this compresses the top O-ring. Also, a touch of anti-seize on the bolt threads might make removal easier next time (but don't over-tighten).  [Response 4: Randy]  Make sure the surface of the block is scraped clean before installing a new gasket (razor blade) and don't ever consider reusing the rubber pieces. I use a light smear of silicone on the heater pipe before putting the Oring on there and then another light coating on that Oring before pressing the pump on (the silicone acts as a lube and helps prevent hanging up, tearing, or twisting; but don't use so much as to have it squeeze out inside) I put a coating of silicone in the groove that the large rubber piece fits in before installing it. I put a coating of silicone on the top of the rubber piece before hanging the waterpump on the two studs. I start the remaining bolts before running the nuts on the studs down with my fingers. Using a hammer handle I apply upward pressure on the bottom of the waterpump to compress the large rubber ring. While maintaining that pressure I snug up the two nuts enough to hold the pump in that position, then I tighten the remaining bolts including the nut/bolt combination that holds the heater pipe in place. I try to wait overnight before adding the coolant to give the silicone a chance to set up.  [Tip: John O]  I wouldn't advise using any sealer like RTV, but spray a little silicone spray on the seals so the pump goes on easily, taking care of the small one on the water tube because it's easy to not notice it slipping out when moving the pump against it.

[Use of RTV vs.Gasket Sealer:] The Haynes manual advises to apply RTV sealant to the gasket. I understand RTV is to be used instead of a gasket. Is it absolutely necessary to use some kind of sealant with the gasket? [Response 1:] RTV may be used in lieu of the gasket but there's no real reason to substitute for a real gasket (I find RTV is more prone to leakage). The trick in putting in a new water pump is to adhere the gasket to the PUMP side only and leave the gasket-block interface free of Permatex (or whatever gasket sealant you're using). The gasket itself provides a great seal without adhesive but adhering it to the pump first assures that it won't slip when you're installing it. [Response 2:] I've replace 4 water pumps in over 15 years of Volvo ownership and never used Permetex or RTV on a pump gasket. I have used the gasket alone and nary a leak in the lifetime of the pumps. I insert two bolts to hold the gasket to the pump before mounting. after hand tightening all the bolts lever the pump upwards to allow the head to seal correctly with the rubber donut on top of the pump and torque appropriately.

Bleeding Air from the Cooling System.  [Query]  After replacing a thermostat or water pump, how do I bleed the air out?  [Response: Jim McDonald]  Very little bleeding should be necessary if you put the thermostat in with the "wiggle valve"[air vent] in the right position[up].  Typically, I only have to add around a liter or so after running the car 'til the thermostat opens.

[Comment:] The quality of aftermarket radiators vary considerably. The brand I use in my shop is "Nissens". One of the nice features of this radiator is the screw cap that holds the sensor in place.

Nissen Radiator Composition.   [Tip from A. Sorenson at Nissens.dk]  Our solder composition is 33% tin and 77% lead [Editor: thereby qualifying as "low-lead".]

 -Plastic-bodied heater water valve cracked; coolant was pumped out
In most of the incidents, drivers did not notice the loss because the coolant was pumped or blown under the car.  In most cases, the first evidence was engine noise, slowing of the car, or other signs of serious engine damage.  [Steve Seekins:] these valves crack longitudinally along the plastic center pipe.
-Heater hose fractured due to aging and internal crack; catastrophic loss of coolant
-Heater hose chaffed against block, rubbing through and failing; catastrophic loss of coolant
-Radiator plastic side tank fractured; catastrophic loss of coolant
-Radiator hose split due to aging and internal crack.  Upper: loss of coolant; lower: catastrophic loss of coolant
-Top radiator hose clamp was over-tightened, cracking plastic neck outlet. Some coolant was pumped out and the engine temp gauge showed overheating but no damage occurred.
-Hose clamp failed; lower radiator hose parted from radiator outlet neck.  All the coolant suddenly drained out of the radiator, leaving only the coolant in the block.  Engine required a new headgasket.
-Coolant Reservoir Hose Became Oil-Soaked at the Clamp and Split.  All coolant was pumped out and the engine overheated.
-Water pump seized due to a bearing failure around the pump shaft, shucking one of the two drive belts.  The remaining belt was sufficient to start the pump turning again, but this resulted in the cast iron pump impeller coming into contact with the back of the pump casing, smashing it and causing loss of coolant.
-Electric frost plug engine heater leaked due to corrosion of the anchoring devicel; slow leak.
-Nobody mentioned a failed water pump shaft seal as a cause of catastrophic loss-of-coolant, merely resulting in slow leaks.

In almost every case, the lack of an "idiot light" caused drivers not to notice the loss until too late.  When the driver finally looked at the temperature gauge, it was invariably far into the red zone, indicating serious overheating.  In almost every case, drivers attempted to drive to a convenient destination such as home, a gas station, or a freeway exit.  This extended drive usually led to further engine damage.   The least damage noted (except in the last instance) was head gasket; in many instances the engine required replacement.

Lessons learned:
1. Assume that your cooling system components have a limited lifespan.  Replace them according to an intelligent schedule.  I replace hoses every six years and the radiator and water valve at year ten.  I replace the water pump either at a convenient maintenance interval or when it starts leaking at the seal.  For turbo cars, assume that the higher underhood temperatures will reduce component lifetimes.
2. Give serious thought to installing a loss-of-coolant sensor and an idiot light wired into your instrument cluster.  "I didn't notice until it was too late" was a universal experience.
3. If you notice smoke, fluid or other evidence of engine distress, STOP and see what the matter is before trying to go any further.  Shut the engine off if you have a loss-of-coolant or oil.

These plans allow you to fabricate and install a low-coolant sensor in your car so that you can detect either slow or sudden coolant leaks and take appropriate action before your engine overheats.  Volvo 760 and 960 cars have these sensors already installed.

Overall Plan.

a) Volvo 740 with Circular Oval Tank.

Using a Nohken float level sensor switch, drill a hole in the bottom of the coolant tank and install the sensor.  One lead is wired to the front grounding plane near the passenger-side headlight, the other back around the engine compartment, through the firewall, to the unused instrument panel lamp denoted "EGR Overheating (Japan Only)."  When coolant is low, the switch closes, allowing 12V from the panel to travel through the switch to ground, illuminating the warning lamp.  You can add a small piezo buzzer to add an audible warning, if desired.  The circuit is fused just behind the panel.

b) Volvo 940 with Rectangular Tank P/N 9142001/2

Volvo included a level float in this tank, but not the sensor.  Buy a "Level Guard" sensor Volvo p/n 3547710 and wire as above.  Make sure you read all assembly instructions below first, especially to confirm you have the float inside the tank.

Bill of Materials:
 

740 Variant: Float Level Sensor Switch: Nohken LS-11P-0A, miniature 10VA switch with polypropylene float and stem and flat flange face. This is available from Scientific Technologies Inc. at 6550 Dumbarton Circle, Fremont, CA  94555-3611, 510-608-3400.

940 Variant: Volvo "Level Guard" p/n 3547710)  approx $15 from Borton's Volvo, http://www.borton.com or from a junkyard off a wrecked 960 car.

c) Instrument panel female metal electrical connector inserted into "C" harness connector:
        a.  740 and 940 before 1994: ell-shaped "C" connector uses Volvo p/n 949542 (likewise "L" shaped)
        b.  940 1994+: flat "C" connector uses flat Volvo p/n 9148152

d) Electrical Supplies, all from Radio Shack (one each unless noted):
Insulated Wire:  20 gauge stranded approx 25 feet p/n 278-1225
Snap Connector 22-18 g, p/n 64-3085
Inline Fuse Holder 5x20mm p/n 270-1238C
GGS 5x20mm Fast-Acting Fuse 3/4 amp p/n 270-1048
Quick Disconnect Connector, Female, .25 inch, p/n 64-4040
Crimp Butt Connector, 22-18 gauge (quantity=2) p/n 64-3037
Shrink tubing for insulating connections p/n 278-1611
Option: Piezo buzzer p/n 273-059 (gives audible warning)
Soldering iron with electronic solder

e) Mechanical Supplies:
Wire ties for securing wire to existing harnesses
"OxGard" conductive electrical grease (from hardware store)
Silicone dielectric insulating grease (from auto parts store)
Volvo 940 applications:  None other required
Volvo 740 applications:  (from hardware store)
Neoprene O-Ring O.D. 1/2 inch, I.D. 3/8 inch
Neoprene Flat Washer O.D. 7/8 inch, I.D. 3/8 inch

f) Volvo wiring diagram to understand your panel connectors.  Here is where Chilton's will finally choke you, and you will be motivated to buy the OEM wiring diagram which is absolutely the best on the market.  Approx. $30 from Ken Cook Inc. (Volvo agent) at http://www.kencook.com/vcna/volvo.html

Assembly Instructions:

1. Volvo 940:
a) Drain coolant recovery tank and remove from car.  Shake the tank to make sure that Volvo installed the magnetic float that activates the Level Guard inside the tank.  (It rattles.  If you can't hear the rattle, install the Level Guard and test it with a multimeter for resistance change as the tank is filled with water.) If your tank has the float,  install the "Level Guard" sensor into the snap hole on the bottom of the tank.  Insert the wire leads into the tank's wiring connector holder on the bottom.  Continue below at step "e)".
If you don't have a magnetic float inside, you can either proceed as though you own a 740, or buy a new tank with a float from Borton's for about $25.
Volvo 740:
a) Drain coolant recovery tank and remove from car.
b) Drill a 10mm hole on the flat surface of the underside, approximately one inch toward the center from the threaded cap
c) Remove the float and install it so that the switch operates in the "N.O." ("Normally open") position.   Test the switch operation with the ohmmeter range on a multimeter: when the float is at the bottom of the switch (corresponding to loss-of-coolant) the switch should close and complete the circuit, reducing resistance from infinite to zero.
d) Remove the fixing nut on the bottom of the coolant sensor switch.  Install the flat neoprene washer on the switch. Feed the switch wires through the coolant fill hole, then into the hole you drilled on the bottom of the tank.  Pull the switch snug.  Install the neoprene o-ring, then the fixing nut.  Snug up the nut until the switch is firmly held without possibility of leakage.  If your hole was oversize, use silicone RTV to seal the gap between the hole and your o-ring.
e) Cut a piece of wire sufficient to reach the grounding panel just behind the headlight.  Using a short piece of shrink tubing and a .25 inch female blade quick connector, crimp the connector onto a stripped end of the wire and add some solder to ensure a long-lasting connection.  Shrink the shrink-fit tubing onto it at the crimp to serve as corrosion proofing.  Clean off the grounding plane connector, install the blade connector and the wire onto the ground, insulate it with some "Oxgard" conductive grease, then feed the wire up the lamp harness back to the coolant tank.  (Maintenance note: this is a good opportunity to clean all your grounds and coat with OxGard to prevent future electrical problems.  Don't use OxGard on any other connectors in the car aside from grounds.)
f) Volvo 740: Install a snap connector to one wire of the float switch and the ground wire.  Again, solder it.  Insulate any exposed wire on the connector with shrink tubing.  This connector allows you to disconnect the level sensor easily.
Volvo 940:  Using a razor knife and some pliers, cut down the diameter of two female snap connectors and squeeze them so as to fit very tightly on the Level Guard lead connectors.  Install one of these snap connectors onto the stripped lead of the ground wire by firmly crimping it.  Place silicone dielectric grease on the connection for corrosion protection and connect the ground wire connector to one of the Level Guard leads.  If you are ambitious, buy the un-insulated version of the snap connectors, solder them onto the wire, and insulate with shrink tubing.
g) Cut a long length of wire sufficient in length to travel from the coolant tank, up the wiring harness at the top of the firewall, thence through the firewall rubber wiring conduit behind the driver-side strut tower, thence into the cabin with an excess of length to reach well beyond the panel.
h) Volvo 740:  Strip, crimp, and solder one end of this wire (using a crimp connector) to the other sensor switch wire.  Insulate where exposed with shrink tubing and apply silicone dielectric grease to the ends of the connector to prevent corrosion.
Volvo 940: Install the other female snap connector onto the stripped lead of the panel wire by firmly crimping it onto the stripped end.  Place silicone dielectric grease on the connection for corrosion protection and connect the ground wire connector to the other Level Guard lead.  Again, if you are ambitious, buy the un-insulated version of the snap connector, solder it onto the wire, and insulate with shrink tubing.
i) Snake the other end of the wire up to the firewall harness and to the lower firewall rubber wiring conduit just behind the driver strut tower.  Use wire ties where appropriate.
j) Cut off one of the smaller rubber wiring conduits in the lower firewall connector just behind the strut tower.  Feed the wire through the conduit into the cabin.
k) Remove the battery negative connector to disable the electrical system.  Remove the driver side kickpanel (two plastic body mounts at the top, pull out.)  Move both the turn signal and wiper handles down, out of the way. Remove the instrument panel (740:  remove plastic fascia plates covering the clock and rheostat knobs, then the two screws holding the panel in place.) (760: See Link.)   (940: unclip using the two side slits midway up the sides of the bezel.  See link.)  Pull the panel straight out and rest it on the steering column.
l) Working from underneath, snake the coolant sensor wire from the back of the firewall wiring conduit up through the panel opening.  Keep it away from the hood release mechanism, any sharp metal edges, and the ignition module, using wire ties as needed.
m) Pull the large 12-position "C" plastic wiring connector out from the rear top center of the panel.  This connector is white and roughly "ell" shaped when looked at from the side (but is flat for later 940s.)
n) Confirm with your wiring diagram which connector you will use for the warning lamp.  In the 1986 740, this is position number 7, numbered on the connector itself, which is not used for any other purpose.  In the 1990 740, this is position 12 on the connector, which connects to the unused "Exhaust Gas Temperature" lamp for Japanese applications.  In the 1995 940, this is position 9 on the connector which connects to the unused "High Engine Temperature" lamp.
o) Cut the coolant sensor wire, leaving enough to reach just beyond the door opening.  Strip and install the in-line fuse holder using soldered crimp connectors and shrink tubing or insulating tape to cover exposed surfaces.  Install the fuse.  Be very careful about soldering near the interior of the car: use a metal guard or shield to keep hot solder off plastic, fabric or leather components.
p) If you want to add the piezo audible buzzer, place it in-line between the fuse and the firewall, again using crimp connectors, solder and shrink tubing.
q) Install the special ell-shaped or flat Volvo metal wire connector p/n as in the parts list above (p/n 949542 or 9148152) to the end of the fuse wire.  While this is crimped in place, you should also add a small amount of solder to secure it.
r) Record the colors and positions of the wires at the "C" connector.  Snap open the back of the connector and insert the coolant connector at the correct position.  Snap it shut, making sure all the wires go back appropriately.
s) Install the Volvo instrument panel lamp at the appropriate lamp position, again per your wiring diagram.  On the 1990 740, the lamp is installed at the second in from the driver's side of the panel, in the unused position.  In the 1995 Volvo 940, the lamp is installed at position 7 from the passenger side of the panel.  If you are confused, use a flashlight and shine it through the empty lamp receptacle to confirm the position from the front.  Just make sure from your wiring diagram that you correlate the lamp position with the wiring position in the "C" connector.
t) Re-install the "C" connector.  Coil extra wire and install a tie to keep it out of the way.  Re-install the panel.
u) Seal the wire passage through the firewall conduit with silicone caulk.
v) Test the installation.
Volvo 740: open the coolant tank and place a pencil on the float so as to depress it to the bottom.  Start the car.  The lamp should go on.  Demonstrate several times to wife and kids what this lamp looks like and what they need to do if it goes on (stop the engine ASAP and investigate.)
Volvo 940:  Using a turkey baster or a siphon, empty the coolant reservoir.  Start the car.  The lamp should go on.  See note above.

Regular Maintenance.  Because of the peculiarities of the wiring within the instrument panel, your bulb may not illuminate when you turn the ignition to KPII before starting.  Hence, periodically test the installation to make sure that the bulb, the sensor, and the circuit operate correctly by performing test v) above.

The crazy way (which I prefer), is to stick a big screwdriver in the way of the fan with the engine idling on a regular day. If the fan stops easily, but quickly spins again, then I guess it's OK. The fancy strobe light Volvo describes seems awfully expensive just to make sure your fan spins right.

Electric Cooling Fan Operation.  [Query] I've had my 1989 740 for a year and just yesterday at the muffler shop, while the car was up on the lift, I peeked in the front end, and lo and behold there, in all its glory was an electric fan in front of the A/C radiator. However it never has turned on, that I know...How do I test it to see if it works?, where is the wiring to the sensor that turns it on?  [Response: Abe Crombie] On an 89 740 model that fan is triggered just for overheat by a switch in tank of radiator that turns on relay on strut tower that feeds power to fan.  If it is a 760 then the relay can be triggered by the aforementioned switch or by a ground out of ECC control unit if the outside temp is over 92 F +/- and you are below 8 MPH and the a/c compressor is engaged.  To test the fan, find the switch on right radiator end tank and pull back the rubber sleeves covering wires and short the two terminals together with a small screwdriver. Key must be on.  If this doesn't make the fan start then go to the relay and check for power supply on one of the two large gauge wires (one is feed and one is to fan motor, so one should be hot). If power is found then disassemble and inspect for cracked solder in relay and repair as needed.

[Electric Fan Won't Turn On] [Symptom:]Engine overheats in 940 while sitting in traffic. I have an electric fan on the front of my radiator. I have never seen it come on - What triggers this fan to come on?
[Diagnosis:] Before you buy a new fan be sure the fan is the problem. The engine *will* overheat standing still in traffic if the fan doesn't turn on to keep the water temp cool enough, especially if the A/C is on. Make sure the fan has not seized first . There is a thermostat switch on the top of the radiator on the passenger side with two wires attached to it. One wire should have voltage to it at all times (engine running). The other wire goes to the fan. If the one wire is hot touch the two together and the fan should turn on. If the fan works then you probably need a new thermostat switch. If the fan doesn't turn on and it has a proper ground *then* you probably need a fan.

Selection: I bought a Mr. Gasket high performance electric fan, 16 inch, heavy duty plastic with ring shroud. this was about 95 bucks. I also bought an adjustable thermostat kit for about 25 bucks. It had a name brand, I think Flex-a-lite or Therma-cool, but it was universal in its application. some members suggested getting the fan and related items from a new 92 or newer 7/900 but i did not have the time to investigate and I do not know of any u-pick-it type salvage yards in the New York Area (anyone know of any?? i would love to check one out.) The fan I bought pulls 1900 cfm on 10 amps. Similar options are the Flex-a-lite, or Perma-cool. A high end option is the Spal fan which pulls 2300 cfm on 23 amps and has a thermostat that connects directly to the cylinder head but the cost is higher, 155+55... I don't know if one needs this kind of air pull but your call.

Swap:

I first slackened the tension of the water pump belt.
Then I removed the clutch fan. there are four 10 mm nuts. I had to loosen each one before I could pull the fan away from the pulley sufficiently to be able to spin the nuts completely off. remove two screws holding shroud to top of radiator. Off came the fan and shroud.
I removed the four studs and replaced them with 6 mm x 1.0 bolts, 12 mm length, 10 mm head. with a lock washer, these bolts fit perfectly. If you never removed a stud before, put two nuts on the exposed thread (do not use the original nuts as the flange prevents good wrench grasp). tighten the nuts against each other. then try to remove the inner-most nut. since it is tightened against the other nut, turning it forces the whole stud to turn and spin out.
Tighten the belt.
I disconnected the inlet and outlet of the intercooler and the radiator/intercooler hold downs. out came the intercooler.
Position the fan closest to the middle of the radiator in hope of being able to re-install the oem shroud ( I cannot see how this could hurt). test fit the shroud. if it will work, keep the shroud in place as you install the fan or better yet reinstall the shroud and then the fan. (Once the fan is in place, it is a tough fit to get the shroud back in place.)
The fan I bought had the four nylon rods with nylon lock washers that push on. they work like a two piece zip-tie. Once one, they cannot come off without breaking them. Position the fan and slide the nylon rods thru the fan holds and through the radiator. slip on the lock washers. Use the rubber gaskets as required to protect the radiator on both sides.. do not over tighten. four snug nylon connectors will hold the fan very well. i used them years ago when i added a tran-cooler to my 72 mustang and it held without a problem. Others have suggested facing a better bracket. Your call.
Once the fan is in place, re-install the inter cooler, hoses, and radiator hold down brackets.
Regarding the thermo, my understanding is that there are three main types. One contacts the coolant in the cylinder head or thru the radiator, one is just a probe that extends thru the rad fins, and one (like mine) has a probe that gets inserted into the upper rad. opening, bends around the opening and gets sandwiched between the opening and the rad house. They supplied a rubber gasket that has a grove in it. The gasket goes against the rad. neck, and the copper tube attached to the probe lays in the groove. the gasket makes for a smoother transition around the tube in an effort to prevent a leak around the tube. It also protects the tube as one tightens the hose clamp around the radiator hose and neck. The probe tube is attached to a thermostat which I connected to the radiator rail to the right of the radiator behind the lights above the battery. Mine is an adjustable thermo from 180-240 degs. I am still playing with the setting.
Wiring: attach the fan ground wire to the thermostat. Get the wires straight, one is for power, one is for ground depending on what direction you want the fan to turn, i.e., puller or pusher. From the thermo connect to any good ground. you have options regarding the power supply.
Connect to a constant power supply if you want the fan to work regardless of ignition key position. This will allow the fan to continue cooling after you have shut off the car. if you have the thermo set low or it fails, the fan could drain the battery.  Or, connect to a power supply that is only powered when the car is running (actually when the key is in the run position...)  With either power supplies, use an in-line fuse (I am not sure how one decides the fuse amps to use. maybe a reader can advise)