Overcooling 1998 S70 t5

[Skiddydiddy]

(first post here, hopefully im using all this right if needs fixed or changed let me know) For some background, I have a decently new to me 1998 S70 t5m about 250,000miles now. Recently did a coolant temp sensor (replaced with meyle) because the fans would kick on briefly along with the dash coolant light coming on during harder acceleration (connector evaporated in my hand while pulling it off assuming that was part of it), otherwise ran fine for its age and didn't stutter or anything before changing. Easy job and seems to have fixed the issue but it's lead to many more quirks. Bleeding the coolant after, the tank cap failed leading to it boiling over at idle (replaced with murray 20psi cap) which seems to have solved that. Also was vaccum filled (held vaccum fine) with generic prestone yellow coolant as I didn't have Volvo coolant on hand.

Now I come to the main issue though that started after the sensor replacement, it seems to take longer to get to operating temp along with overcooling to about 155f while driving. Had a new non OEM thermostat from last owner, to be safe did a new Genuine Volvo thermostat and seal, double checking it was positioned correctly today and the issue still persist though maybe slightly better it seems. Ambient temp during this is about 85-90f fyi.

-Testing I've done at idle, as mentioned takes a while to build temp but does get to about 211f before I kick on the ac to force the rad fan on, where it then quickly cools to about 155-160f. Using my cheap temp gun on the thermostat housing and upper rad hose reads pretty close though maybe 5-20 degrees higher than the scan tool. Reads at about 4 to 5 o'clock starting out but does eventually get to just above 3 before I turn the fan on.

-During driving watching my scan tool, it builds temp when stuck at lights to around 170f, and on the longest uninterrupted straight I took (going about 55, 5th gear, 2k ish rpm) dropped to about 155f. Averaging about 162f during the drive. Reads about 3.5 to 5 o'clock on the dash corresponding to temp ovb.

So as I said, new thermostat, coolant temp sensor, rad cap, new coolant, and still overcooling it seems by about 30 degrees (near 190f is correct operating correct-?). I have a fan relay coming already as it seems to not kick the fans on when it should, low speed should start at around 192 if I'm correct. Anyone else heard of anything like this issue? Change to volvo coolant? Test or try new sensor? Maybe coolant is somehow passing the thermostat in the housing? Know it's not a huge issue now but I'd rather solve it before it possibly becomes worse in winter. Thanks for reading.

[RickHaleParker]

So as I said, new thermostat, coolant temp sensor, rad cap, new coolant, and still overcooling it seems by about 30 degrees (near 190f is correct operating correct-?).

Did you bleed all the air out of the system? An air bubble can sit directly on the coolant temperature sensor. Air is a very good insulator. This insulation causes the sensor to report a falsely low temperature. If you have a IR thermometer, use it to do a sanity check.

Did you get the Jiggle Valve aligned upward when you dropped in the new thermostat?

[Skiddydiddy]

So as I said, new thermostat, coolant temp sensor, rad cap, new coolant, and still overcooling it seems by about 30 degrees (near 190f is correct operating correct-?).

Did you bleed all the air out of the system? An air bubble can sit directly on the coolant temperature sensor. Air is a very good insulator. This insulation causes the sensor to report a falsely low temperature. If you have a IR thermometer, use it to do a sanity check.

Did you get the Jiggle Valve aligned upward when you dropped in the new thermostat?

It was vaccum filled with coolant last week still had the issue, when I did it today just left the cap off until it ran to temp and cycled the heat to bleed the air. The ir thermometer reads about 5-20 over what the scanner says when facing the upper rad pip and thermostat housing. Valve was aligned towards highest point, facing towards front middle of car.

Really puzzling situation, at the moment I think it's most likely some wiring issue giving me readings just slightly off enough to seem cold but also realistic enough with the temp gun? Only other thing I could really think of is the housing is damaged and coolant is passing around it but it didn't look like it to me during replacement

[RickHaleParker]

The IR thermometer reads about 5-20 over what the scanner says when facing the upper rad pip and thermostat housing.

That sounds like your new sensor is lying to you. If you bought it from a discount vendor you may of got one of the seconds grade parts. ... If you got it from a big box retailer, may of got one of the seconds grade parts. Who did you buy it from?

If you have not pitched the old sensor, you might try putting it back in and see what changes.

[abscate]

If your temperature gun is reading the same 160F about all that’s left is a defective thermostat. That’s really cold and the mileage will suck as well as heat won’t be good in winter

[Skiddydiddy]

Did another test right after driving to work, scanner was reading 170f, ir temp gun 210 at the thermostat housing and 190 at the rad pipe. So I'd say that pretty much narrows it down to it being the sensor in my opinion, (nearly everything else has been changed or tested since it started) so I'm gonna get another coming soon, anyone know where I can get an oem / oem equivalent? Also does anyone know how much resistance it's supposed to show at what temps so I can verify? Id like to check it directly, and if there's a point further back in the harness to see if there's an issue with the wiring heading to it. I can't seem to find it myself.

Last one was a mayle from ipd which might just be a lemon, or less likely the connector/wiring has some issue after I moved it around in the install. Unfortunately didn't keep the original sensor to check against

[scot850]

I think the OE was a company with a name like Vernat. Not sure if you get them here. This is a part I only us OE Volvo for as it is what I consider a critical part.

Also check the connector and the pins in it for failure. They can become brittle with age. That includes the connector body.

Air locks on the thermostat in my experience is fairly common until the car has had a good run then it may 'burp the remainder of the air out.

If you can get the car nose in the air after a run it may help remove the air if any remains.

Good Luck!

Neil.

[RickHaleParker]

Also does anyone know how much resistance it's supposed to show at what temps so I can verify?

For Volvo factory part number 9186486.

1998 Volvo S70 T5 ECT Sensor Resistance Chart

Temperature (°C)	Temperature (°F)	Expected Resistance Range
-10 °C	14 °F	8,260 – 10,560 Ω (approx. 9.4 kΩ)
0 °C	32 °F	5,400 – 6,100 Ω (approx. 5.7 kΩ)
10 °C	50 °F	3,500 – 3,900 Ω (approx. 3.7 kΩ)
20 °C (Room Temp)	68 °F	2,280 – 2,720 Ω (approx. 2.45 kΩ)
40 °C	104 °F	1,100 – 1,200 Ω (approx. 1.15 kΩ)
80 °C	176 °F	290 – 354 Ω
90 °C (Operating)	194 °F	240 – 260 Ω
100 °C	212 °F	180 – 190 Ω

Quick Diagnostics:

• Unplug the harness connector from the ECT sensor before measuring resistance across the two pins.
• A healthy sensor drops resistance smoothly as it warms up. Watch for erratic spikes or "dead zones."
• The ECU sends a 5V reference signal to the harness plug when the ignition is switched on.

[aeg]

OE was Valeo/SWF. But it looks like they were discontinued this year. So unless you can get hold of one... I would probably go with the (expensive) Volvo blue box part, which you can still get for now.

Note that if the Meyle ECT is your problem, then your car is not actually taking too long to warm up; the temperature gauge is showing a lower temperature than actual. In fact, the engine may be at risk of reaching dangerous temperatures, since the fan is never going to kick in.

[aeg]

Just saw BlackVLVParts has a Volvo 9186486 for a good price.