posted by
someone claiming to be charles
on
Sun Sep 22 09:32 CST 2024 [ RELATED]
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Hello everyone,
I have a 1994 Volvo 940 Turbo with 140K miles. Last winter, the engine struggled to warm up; the temperature gauge barely moved and never reached the middle, resulting in poor heat and an engine that was hardly warm to the touch. I did a coolant flush, replaced the thermostat twice with new coolant, and bled the system, but the issue persisted.
This summer, everything seemed fine—the engine warmed up properly, the temperature gauge reached the middle, and the heater blew hot air. However, with the cooler weather returning, I'm encountering the same problem again. I would really appreciate any help, as winter is approaching.
Thank you in advance!
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posted by
someone claiming to be charles
on
Tue Sep 24 20:23 CST 2024 [ RELATED]
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What are the chances of getting two faulty new thermostats?!
It’s surprising, but both had issues. Upon closer inspection, neither of the thermostats I bought was fully closing. A barely visible 1mm gap was preventing them from sealing properly. I ended up buying a third thermostat (aftermarket) and now everything is working fine.
Thank you all for your help, and God bless!
Charles
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We had someone here just a few months back with a similar issue. Turned out the engine simply wasn't being given enough of a chance to fully warm up. Can take a good 15 minutes or more to reach maximum operating temperature, longer in really cold weather. Is the upper rad hose hot to confirm the thermostat is hot enough to open?
If both the dash gauge and the air coming out of the vents remain colder than normal after a good long run then that says the engine is overcooling. About the only way for that to happen is for the thermostat to stay open (stuck debris or a broken spring), opening too soon (incorrect thermostat, needs to be 85-91 deg C, check the stamp on it then test in boiling water bringing it up to a boil slowly) or not being properly installed (lip inside the rubber gasket, weep hole up high, spring down toward the block).
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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 Dave,
It looks to me you have covered all the bases around a thermostat or just plain cold weather without a long enough drive.
I know very little about a 900 series except their body shape and maybe the drivetrain.
I have this question though about a turbo 900 having electric fans?
I can only figure that it might have a A/C condenser fan or it could also be a helper fan since it’s a foot fancier turbo. 😊
Maybe the owner doesn’t realize that it’s not supposed to run all the time like a viscous clutch driven can appear to do.
Maybe if it doesn’t have all electric maybe the viscous clutch is running solid and its thermostat spring is stuck.
He needs to give it a spin manually before and after a hot engine run. The radiated heat should make it spin more freely than when it’s cold.
He said it was ok this last summer but as the world tilts and so should the logic scale as he has raised the point of variations with the term lately?
Phil
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Hey Phil,
The 940s and later 700s got electric cooling fans attached to the back of the rad. Even flat out they shouldn't be able to noticeably cool an engine if the thermostat is properly closed based on upper block coolant temp. Initially these were single speed fans controlled by a thermostat inserted into to the upper right corner of the rad connected to a fan relay under the hood. For LH 2.4 these became a two speed fan with the relay being controlled by both the ECU (based on the block temp sensor reading) as well as a pressostat on the lower A/C condenser rail. I think with effort a few have been able to retrofit the 740 electric fans to a 240, the main issue being a temp sensor if you don't want it running full time.
Note for LH 2.4 owners reading here, many of the later rads (ike Nissens) are universal fit and have a thermostat hole in the upper right corner. They come with a rubber grommet and plastic plug for it (check if it's hidden underneath). Many (including me now) recommend using a couple of black UV-proof zip ties around the plastic side tank so it can't blow out, but please realize the over-pressure weak point in the cooling system then becomes the heater valve and heater core, which are even more fun to deal with.
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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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Dear Dave Stevens,
Hope you're well and stay so. I've long thought that the coolant overflow tank's cap gives pressure relief to the cooling system.
No radiator plug is needed in a car with an in-radiator temperature sensor that controls the electric fan. An example a '93 940 with Rex-Regina fuel/ignition management.
About 15 years ago, the in-radiator plug in a '94 940 - not needed for a temperature sensor given Bosch fuel/ignition management - worked loose. Happily the day was cool (about 50°F / 10°C) and the trip was short.
On my return, I topped-up the coolant. I replaced the plug and used brass wire to secure the new plug. I drilled a small hole in the radiator's side-tank fin, through which I put the brass wire that I ran through the slot in the plug's top. I then wrapped the wire around the base of the side-tank's nipple for the in-radiator authomatic transmission fluid cooler. This secures the plug.
I'd recommend securing the press-fit in-radiator temperature sensor or the plastic plug (where no sensor is needed).
Hope this helps.
Yours faithfully,
Spook
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Dear Dave Stevens,
Hope you're well and stay so. I've long thought that the coolant overflow tank's cap gives pressure relief to the cooling system.
No radiator plug is needed in a car with an in-radiator temperature sensor that controls the electric fan. An example a '93 940 with Rex-Regina fuel/ignition management.
About 15 years ago, the in-radiator plug in a '94 940 - not needed for a temperature sensor given Bosch fuel/ignition management - worked loose. Happily the day was cool (about 50°F / 10°C) and the trip was short.
On my return, I topped-up the coolant. I replaced the plug and used brass wire to secure the new plug. I drilled a small hole in the radiator's side-tank fin, through which I put the brass wire that I ran through the slot in the plug's top. I then wrapped the wire around the base of the side-tank's nipple for the in-radiator authomatic transmission fluid cooler. This secures the plug.
I'd recommend securing the press-fit in-radiator temperature sensor or the plastic plug (where no sensor is needed).
Hope this helps.
Yours faithfully,
Spook
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Hi Spook,
Yes, Regina got the thermal fan switch in the rad, and yes, it's safest to also secure it with zip ties or wire through the fins and around the plastic tank. As I mentioned, the LH 2.4 system got a two speed fan and that thermal switch could no longer be used. Originally Volvo made the rad without the plug hole, then went for a universal fit using a plastic plug that you push into the rubber grommet, or you can simply insert an old thermal switch and leave it disconnected. Note that the LH 2.4 B230FT with intercooled turbo uses a slightly different sized rad and never came with Regina, but the rad often still comes with a hole to plug.
The rad cap on the expansion tank is indeed the safety valve, but you still need to be aware of the weak points that can fail under continual stress and sudden high pressures. I've had one rad plug blow out on the highway in our 940 LH 2.4 NA. Whether or not the cap was also relieving pressure at that moment is uncertain. I replaced the plug and secured it. Next to blow a few weeks later was the heater valve. It was the 20+ year old original one, which I was quite aware are known to fail, so my fault for not replacing it sooner. I replaced that with an unused, but older MTC valve of the same original half metal, half plastic design and it blew open on the next highway trip. Okay, woah, maybe something's not normal here! I was starting to get worried the next thing to go might be the heater core, which was still the original in this car (the one 940 and one 740 heater core I've had to replace is an exercise I'm in no hurry to repeat). It was then I started to investigate closer. Although the coolant looked normal and there was no smoke in the exhaust, I suspected a head gasket leak, which was quickly confirmed by one of my Volvo indies. Idle the car with the rad cap off until the thermostat opens and if it suddenly boils over then it's the head gasket (With the B230 engines you should be able to idle almost indefinitely with the rad cap off).
As long as we're on the topic of cooling system pressure and weak points, here's from some of my old notes that I've posted here before:
The coolant expansion tank caps used are as follows:
- grey = 150 kPa (22 psi) superseded by the green cap
- green = 150 kPa (22 psi) standard issue for all 700/900s
- white = 100 kPa (15 psi) uncommon (used in one of the 240 variants in Europe)
- black = 75 kPa (11 psi) standard issue for all 140/240s
It's always best to use genuine Volvo or at least a reputable OEM brand. The green caps provide for optimal engine operating conditions in 700/900s. Some people believe the lower pressure (240) black cap doesn't stress the plastic sides and fittings of the rad tank as much, especially in a hot turbo engine compartment and especially as the rad ages. With that thinking in mind I've decided the trade off is worth it and use a black cap in my 940 turbo, but have kept the green cap in my 940 NA. Remember that the higher pressure caps prevent system boilover in high temperatures and allow higher engine operating temperatures, important for good fuel economy.
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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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