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Hey gang, got an odd one for you.

My car used to sit rock solid at 170 (has a 170 degree thermostat) but within the past year that's become more variable depending on if I'm sitting idle or driving.  If sitting idle in 95 degree weather, it will go a little past half which I know isn't bad but the fact that it used to sit rock-solid at 170 regardless of weather tells me there's something wrong and even though its not severe it's annoying lol.

I've changed the fan clutch, thermostat, water pump, checked fanbelt tightness, changed coolant, used a flushing chemical, and even got a brand new radiator but while the temperature isn't moving as much, the needle still moves depending on if idling or driving.  There is definitely rust in the system because the PO used tap water and ever since I got it years ago, its been a game of 'how much rust will come out with this flush' (its always less but there nevertheless).

I've also cleaned the temp gauge harness connector/sensor outlet and nothing has changed.  I'd have thought it was the temp gauge if the car didn't go back to 170 like it used to while driving - but since it does, it tells me the temp gauge hasn't lost calibration and the coolant temperature really is changing.

Any ideas?

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7 minutes ago, siteunseen said:

I've had to use an air compressor to clean my radiator in the beginning of grass cutting season down here. The lazy guys blow the mess into the streets and it gets in my air filter and radiator 

I'd give that a shot but I got a new radiator and took it for its maiden voyage last Thursday when I noticed the car still had the issue

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4 hours ago, siteunseen said:

New info. You may have some kind of air in the system if it started with the new rad?

I'd let it run, idling, until you see flow under the cap. Rev it up pretty high and let it burp. Then top it off.

Goodluck!

Unfortunately the problem with the old rad/thermostat/water pump/fan clutch persists with the new rad/thermostat/water pump/fan clutch even after burping it.

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did you check the new thermostat before installing it? new ones can be bad. 

Also, is the valve central in the thermostat or offset to one side? if offset, I think its possible to install it so it can't open fully. (one side of the thermostat housing is shallower) 

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8 hours ago, jonbill said:

did you check the new thermostat before installing it? new ones can be bad. 

Also, is the valve central in the thermostat or offset to one side? if offset, I think its possible to install it so it can't open fully. (one side of the thermostat housing is shallower) 

This was an aftermarket thermostat with an off-set valve.  I'd definitely agree that could be the case but the thermostat I had in there previously was only a couple years old and a genuine nissan part with a centralized valve but after changing to this thermostat the issue didn't change.

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hmm. that could be your clue. eventually that will worsen over time and affect temp. Maybe it worsened a bit when you noticed the change in temp. Will also corrode your cylinders (and clean your piston tops)  if the car sits for any amount of time. 

If you think you have a blown head gasket....I would encourage you to pull the head and fix it.

J

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Are you sure the coolant passages in the engine are not clogged from it being so rusty as you described? The flow rate of the coolant could be way down from what it's supposed to be, without the engine experiencing rusty passages.

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8 minutes ago, Andrew@TheZStore said:

Are you sure the coolant passages in the engine are not clogged from it being so rusty as you described? The flow rate of the coolant could be way down from what it's supposed to be, without the engine experiencing rusty passages.

Good point - is there a way to check/fix that without sending the head and block to a machine shop?

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4 hours ago, chaseincats said:

Oil looks good - it's always thrown a small puff of white coolant smoke on a hard acceleration gear change though

Check your spark plugs.  Use a borescope.  

How can you tell it's coolant smoke?

I had a leak at the back of the head.  Not obvious.  Passenger side.

 

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2 minutes ago, Zed Head said:

Check your spark plugs.  Use a borescope.  

How can you tell it's coolant smoke?

I had a leak at the back of the head.  Not obvious.  Passenger side.

 

I believe its coolant since its white (not blue) and has a sweet smell

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Lots of ways or combinations of ways to confirm blown head gasket.

Smell in the presence of white exhaust.....assuming your sniffer is reliable.

Borescope is a great idea. Might be something you can rent from an auto parts store. The leaky cylinder will have part or all of the piston clean. Often the spark plug will be unusually clean too.

Leak down and / or compression test can contribute to the evidence.

Watching coolant level and seeing that it reduces.

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3 hours ago, Andrew@TheZStore said:

Are you sure the coolant passages in the engine are not clogged from it being so rusty as you described? The flow rate of the coolant could be way down from what it's supposed to be, without the engine experiencing rusty passages.

Any way to clear these without disassembling the head/block and shipping it off to a machine shop?

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If you are having coolant blockage issues. You might be able to flush it out with the head off. Many times the cylinder head gaskets have some small holes in them. Maybe some of these are getting blocked. Maybe even temporarily.

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You can try to do a flush on the engine. Some people use a hose to get good water pressure through the entire engine to try and push debris out. There are also Coolant system additives you can purchase to help flush the system before doing a full coolant change. 

Funnily enough, ChrisFix's YouTube videos on the coolant system additive and flush are quick, easy to understand right to the point.

https://www.youtube.com/watch?v=s--5ft5YiHg

https://www.youtube.com/watch?v=g8YZF5cW7-A

 

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Posted (edited)
On 5/24/2022 at 5:29 PM, Andrew@TheZStore said:

You can try to do a flush on the engine. Some people use a hose to get good water pressure through the entire engine to try and push debris out. There are also Coolant system additives you can purchase to help flush the system before doing a full coolant change. 

Funnily enough, ChrisFix's YouTube videos on the coolant system additive and flush are quick, easy to understand right to the point.

https://www.youtube.com/watch?v=s--5ft5YiHg

https://www.youtube.com/watch?v=g8YZF5cW7-A

 

I used oreilly's generic flush chemical a month or so ago and did the low budget fix of 'the garden hose in the thermostat housing' which got a fair bit out but didn't change what the gauge had to say.

Edited by chaseincats
grammar
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If I were going to try to flush a block out. Take the head off and use a prressure washer through the top of the deck and the water pump holes. Messy but you'll be amazed at what comes out.

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Prestone back in the day made a back flush kit that hooked to the heater hose connections. Thermostat had to be removed . Run the chemical in the block for a set period and back flush again. Worked amazingly well. My two cents from an old guy.

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5 hours ago, Yarb said:

Prestone back in the day made a back flush. Run the chemical in the block for a set period and back flush again.

I don't know what they used back in the day, but last time I looked the label today says citric acid.

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