2000 S70 Coolant Temp Gauge Fluctuating

[850oldschool]

If you apply oil, make sure to rinse it out of the drive recess with solvent, because the lubrication will make it easier for the bit to twist out without loosening the screw.

[tjmartin317]

Don't get too complacent on it bring an easy job. The thermostat housing has 2 x T30 or T35 threaded screws in them that like to seize in place.

With this being the hard part, I'm still going to consider this an easier job than anticipated. Will blast it with PB before hand and apply some anti-seize after.

I'm guessing no coolant will be left in the overflow reservoir in order to get the level down below the thermostat. Or would whatever the reservoir is showing act as the "highest point" in the system meaning that, once it's empty (or at least below the housing) I can proceed?

[scot850]

You will have to lower the level overall below the height of the thermostat. There is a drain plug usually in the LH lower corner of the radiator, but many prefer to just disconnect the lower radiator hose as the drain plug is plastic and prone to fragility when new let alone with age.

The header tank will drain as the hoses are probably higher than the thermostat.

Neil.

[454cid]

I just pull the housing, and don't worry about the loss. Coolant always goes everywhere for me, whenever I open the system up on any vehicle. So catching it is always a percentage depending on where I have a pan. It always hits a cross member, bracket, or something and travels multiple directions at once, much wider than the pan. For as little that's lost when doing a thermostat, I don't even worry about it.

If the drain petcock is readily accessible, and you can put a hose on it, that would be your best bet in contain it, if you want to collect it.

On my 99 S70, the holes were through holes. I think my 96 850 had blind holes. If you've got blind holes, make sure you blow them out with some air to get coolant out, and then maybe use brake cleaner, and blow them out again.... with a rag covering the area when you do it. If you don't have an air compressor, maybe soak the liquids up with twisted paper towel?

[wizechatmgr]

I just pull the housing, and don't worry about the loss. Coolant always goes everywhere for me, whenever I open the system up on any vehicle. So catching it is always a percentage depending on where I have a pan. It always hits a cross member, bracket, or something and travels multiple directions at once, much wider than the pan. For as little that's lost when doing a thermostat, I don't even worry about it.

If the drain petcock is readily accessible, and you can put a hose on it, that would be your best bet in contain it, if you want to collect it.

On my 99 S70, the holes were through holes. I think my 96 850 had blind holes. If you've got blind holes, make sure you blow them out with some air to get coolant out, and then maybe use brake cleaner, and blow them out again.... with a rag covering the area when you do it. If you don't have an air compressor, maybe soak the liquids up with twisted paper towel?

Precisely what you said, it typically isn't more than a cup or two. Just rinse the ground after to make sure no cats or dogs drink it.

[foggydogg]

2 x T30 or T35 threaded screws in them that like to seize in place.

With this being the hard part, I'm still going to consider this an easier job than anticipated. Will blast it with PB before hand and apply some anti-seize after.

I'm guessing no coolant will be left in the overflow reservoir in order to get the level down below the thermostat. Or would whatever the reservoir is showing act as the "highest point" in the system meaning that, once it's empty (or at least below the housing) I can proceed?

T40, use a fresh bit.

IMG_0289.JPG (209.33 KiB) Viewed 439 times

Yes on the juice gone in the tank, try the drain on the radiator but be gentle, it's plastic. Shouldn't be real tight unless it has Muck of Ages on it. It seats with an o-ring.
Our old friend Robert has some thoughts on this issue,

Some of the challenges here depend on whether it's ever been done before.
The poor performance may simply be a result of low coolant temps confusing the computer.
Don't be tempted to put a 180 in it, use the factory 192, which I think is like 90c, or something.

[foggydogg]

It does look like an easy fix, hence why I'm not super spooked to do it. But when electrics get involved, I get nervous. Hence why I'm forever baffled by my 50 year old fuel injected VW... but that's a whole other story

The bucking could very well have to do with letting my buddy try driving it. Happens very rarely though, not super concerning.

I'll see what I can do about the coolant temp sensor. I got it from Autozone because I work in a GMC parts department and have a really strong relationship with that store. Always feel bad about any inconvenience I cause the store for personal parts, but worst case scenario, I could just hang on to it for now.

This aftermarket brand seems to have a good rep for the sensor, FCP can be a bit slow on shipping though in case you need to get your ride going.
https://www.fcpeuro.com/products/volvo- ... -9186486-1
The new thermostat should come with a new rubber gasket. The screws don't need to be two-fisted tight, the rubber seal does the work.
I just did this on my '98,

IMG_0286.JPG (334.71 KiB) Viewed 434 times

Used a piece of sandpaper held flat on glass to scrub the bottom of the housing flat enough for me.

[454cid]

I just did this on my '98,
IMG_0286.JPG
Used a piece of sandpaper held flat on glass to scrub the bottom of the housing flat enough for me.

I'm surprised it wasn't already flat. It's not like there would be compressed and hardened remnants of paper gasket. What's all the black stuff on the old thermostat?

Something, I think that's worth mentioning is that unless the upper hose is being replaced, or there is a leak there, I would not remove the hose from the water neck. It's more work, and disturbing it may make a problem were there previously wasn't one.

[BEJinFbk]

Call me crazy, but if it IS a bad stat,
it sounds like the sensor is working just fine.
If it ain't broke...

[foggydogg]

I just did this on my '98,
IMG_0286.JPG
Used a piece of sandpaper held flat on glass to scrub the bottom of the housing flat enough for me.

I'm surprised it wasn't already flat. It's not like there would be compressed and hardened remnants of paper gasket. What's all the black stuff on the old thermostat?

Somebody had already been there; the flange ears showed evidence of over-tightening, the aftermarket ("RadMod"?) thermostat seal had weeped and caused a bit of corrosion. Dunno what the gack was, threw it in the trash.
[/quote]
Something, I think that's worth mentioning is that unless the upper hose is being replaced, or there is a leak there, I would not remove the hose from the water neck. It's more work, and disturbing it may make a problem were there previously wasn't one.
[/quote]
See 'Somebody...', above, aftermarket clamp and the hose was twisted. Came off without issue. I used a fair amount of heat on the screws, and didn't need the added complication of having the hose in the way. I tend to agree on the radiator side, but the thermostat housing side isn't normally a problem for me.