# Question about cooling system temps 90 sentra



## ahardb0dy (Nov 9, 2003)

So this past April I had an issue with the thermo switch that controls the electric fan, no matter how hot the engine temp got the fan did not come on. So I ended up ordering a new thermo switch and thermostat from rockauto, figured I would replace the thermostat as it was never replaced since I owned the car.

I replaced the thermostat and the thermo switch, let the car sit over night so the RTV could dry, than I flushed the cooling system using a flush, filled the system, bled the air through the bleeder screw and repeated 3 times. I drained the radiator, engine block and also drained and cleaned the over flow bottle. I put in new anti freeze mix and all was fine until recently.

I noticed when driving the engine temp gauge is sitting where it normally does right around the 1/4 mark on the gauge but I also have a mechanical Autometer water temp gauge installed, I have the sender installed in the water outlet on the block, ( I drilled and tapped the hole like the JDM engines have), the Autometer gauge runs about 180 degrees while driving but lately when in traffic it is getting up over 200 degrees. It hardly ever used to go above 200 unless it was mid summer and in the high 90's ( live in Florida near Orlando).

So as a test Thursday when I got home from work I sat in the car letting it run to see when the electric fan would come on, it finally came on at 208 degrees (autometer gauge) with the stock gauge just below the half way point. 

Both fans come on fine when I turn the AC on.

I thought it may be a water pump issue but noticed when I give the car a little gas the temp will start dropping right away so I think that shows the water pump is pumping fine.

Today I removed the thermo switch, the gauge sender (yellow plug) and the autometer sender and cleaned them all.

The yellow plug sender broke in half while cleaning it (plastic broke off the metal) so I cleaned and tested one I had extra from my pathfinder, same part.

The thermo switch is supposed to turn the electric fan on at 185 degrees but I do not know what the stock gauge equals in terms of temp since their are no numbers on the gauge, and the yellow water temp sender is located near the front of the thermostat housing but my autometer gauge sender is in the water outlet so I would think the autometer gauge would be reading a higher temp as that water is coming straight out of the engine.

What do you think?

Also where is the sender, if there is another one that is supposed to be just for the gauge? I read in another thread that the yellow sender is actually for the ECU??

Thanks.


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## ahardb0dy (Nov 9, 2003)

almost forgot to ask this,

The engine idles dead on at 850 RPM, when the electric cooling fan comes on the rpm's drop to about 300 and one time the engine actually stalled.

If I turn the AC on (let me say I do not have the AC belt on at this time since the AC compressor is bad but turning the AC on still turns both fans on), anyway if I turn the AC on both electric fans come on fine but the RPM's will raise to about 1100.

Any idea why the RPM's do not raise when just the cooling fan comes on??

Thanks.


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## bob89sentra (Sep 15, 2005)

Send me your e-mail address, I have gone through this and so much more. I think I might have some of the answers you seek.


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## ahardb0dy (Nov 9, 2003)

sent PM, thanks


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## ahardb0dy (Nov 9, 2003)

So I found the other sender for the gauge few minutes ago, pulled it out and cleaned it, going to test it in a couple minutes. Also have an extra one from my pathfinder going to test it also as they appear to be the same. Best one goes back in.


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## ahardb0dy (Nov 9, 2003)

Tested both, extra one seemed like it was closer to spec, installed it and took a test drive, got home and water is pissing out the bottom !! Popped the hood and a hose is leaking !! Too dark to look at it tonight, will be pulling the air cleaner back off again tomorrow !!!

Temp still gets up to 209 on the Autometer gauge before the fan comes on


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## ahardb0dy (Nov 9, 2003)

Replaced the heater hose and pulled the hoses off the wax element housing, one at a time and ran water thru the radiator to flush the lines and to see how much flow came out, flow was good going into and out of the wax element housing. Bob was telling me how his wax element housing had debris in it that was restricting flow to the thermostat.

Fan still coming on at exactly 209 degrees on the Autometer gauge, just below half way point on stock gauge, thermoswitch fr fan is supposed to turn fan on at 185 degrees, no idea what temp 1/2 is on stock gauge numerically.


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## ahardb0dy (Nov 9, 2003)

My neighbor is lending me a infrared thermometer going to take some temps at various locations under the hood to see what kind of temps I'm getting.

Temp stays right at 180 while driving


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## ahardb0dy (Nov 9, 2003)

I drove the car to work and back today, was a little hard on it on the way home, got home and I can smell antifreeze, checked under the car no water leaking anywhere, funny part is, I don't have antifreeze it the system right now ?????


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## jdg (Aug 27, 2009)

Unless you drained the water out of the bottom of the block, you probably got a bit of antifreeze leftover in there...somewhere...hidden from view. Also, if I can throw it out there, maybe the smell is actually hot steamy water mixed with scale/sludge/slime/crud from the water passages in the block itself.

From post #2:


> Any idea why the RPM's do not raise when just the cooling fan comes on??


Probably because there isn't a load from A/C compressor, just the electrical load of two more fans running...not nearly as much of a load to warrant an idle increase.

Also, in the first post, you said if you give it a bit of gas, the temps drop a bit, and you figured that was a sign of a good water pump. In my experience, among other things, that could be a sign of a bad water pump, e.g. bent impeller blades on the internals of the pump itself, broken impellers, etc., a water pump that won't or can't pump efficiently at lower rev's.


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## ahardb0dy (Nov 9, 2003)

Thanks, by draining the water from the bottom of the block do you mean by removing the drain plug on the block? or ae you referring to water that won't drain because it may be lower than that drain plug?

When I press the AC button and both fans come on, ( like they are supposed to when the AC is engaged), compressor turning or not, the RPM's do raise, when the one fan comes on when the thermo switch reaches the temp that it turns the one fan on, the RPM's do not raise.

I wouldn't doubt the water pump is bad it's 22 years old, may replace that soon, I can imagine what it looks like on the inside !!


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## jdg (Aug 27, 2009)

Little bit of everything above...

Drain plugs - Yep, the one on the block. Obviously, the radiator drain plug won't do much good. And the block drain plug might be a tad bit above the lowest of the low parts of the water jackets in the block. Might be the case that you have to jack up the back of the car or jack up one side or both to get that last little drop of water out of the block from the drain plug. I dunno. Never tried that hard.

A/C button - engine idles up and both fans should come on because of both the additional heat load from both the engine idling up and the A/C condenser being used as well as the additional working load from the A/C compressor itself. Normal ops.

Thermo switch - one fan comes on to cool the water only. No real additional electrical load from one fan hence no real need to idle up. Normal ops. Maybe at an even higher temp, the 2nd fan will come on. I don't know and don't think I want to try it out either 

22 year old water pump - Ya, one thing I forgot to mention would be the scale and crud that may build up on the impeller blades themselves.
Ever had a house fan that had dust build up on the blades?
Ever cleaned off those fan blades and noticed how much quieter it was afterwards?
Same thing applies here. That crud on the impeller blades creates turbulence that could impede low rpm pumping thereby making it heat up a bit.
And besides, the thing is 22 years old! It's time to recycle it!


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## ahardb0dy (Nov 9, 2003)

Timing chain is 22 years old too !!

So, 2 other questions for you:

1. I replaced the thermo switch as the one that was in the car ( probably the original one)was not turning the fan on, do you think the water pump being old, the impeller possibly being worn or having crud on it could cause the fan to come on at a higher temp? As I said on my auto meter gauge the fan comes on at exactly 209 degrees, the thermo switch per the FSM says it should come on at 185 degrees.

The temp hardly ever went over 200 unless it was mid summer high 90's now it does everyday, when I'm in traffic or stopped. I guess if the water pump isn't moving enough water at low RPM and would make the engine run hotter right?

2. Sometimes when I come to a stop sign or red light and push the clutch in the rpm's will drop real low and engine will run rough, If I rev the engine once it the rpm's return to normal and tach stays rock steady at 850. I was thinking maybe the dash pot is not adjusted properly, I know the dash pot is like a little shock and when the throttle is closed it hits the dash pot, I'm assuming the shock is supposed to let the throttle close slowly?? Not sure on this it just makes sense. What do you think??

Thanks for your help. Appreciate it.


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## jdg (Aug 27, 2009)

I wouldn't think the water pump being worn would cause the fan to come on at a higher temp...2 unrelated deals. However, with that being said, maybe the same crud that's on the pump is also on the sender.  Also, is your auto meter gauge bulb in exactly the same place as the thermo switch? Probably not. Therefore it follows that the two are probably reading two different temperatures in the block. I also would think that the fan wouldn't come on until 209F rather than 185. Seems to me like 185F is more like the thermostat opening temp and not the "kick on the fan" temp.

2 - No idea. The carb'd 1.6L isn't my bag...but...makes sense to me, especially being 22 years old  Might be time to spray down the whole works with a couple dozen cans of carb cleaner and see what happens.

Timing chains are 22 y/o? Maybe...uh...time for a new tensioner? Do the '90 models have an upper tensioner like the later models?


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## ahardb0dy (Nov 9, 2003)

I removed all the temp senders, gauge, ECU and the thermo switch and cleaned them all, they were not bad looking. The autometer gauge sender is in the water outlet at front of the block, I drilled and tapped it. The thermo switch is in the top housing for the thermostat. I borrowed a infrared thermometer to check what the temp is at each location, will do this Saturday.

This is what the FSM says about the thermo switch:










I take care of my car it's just this problem driving me crazy. Engine and TB are clean.

No idea if the timing chain has upper guides, this is what the FSM shows:


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## jdg (Aug 27, 2009)

ahardb0dy said:


> I removed all the temp senders, gauge, ECU and the thermo switch and cleaned them all, they were not bad looking.


Like everything else, looks aren't everything.
IMO, if it isn't overheating, boiling out water, wrecking the oil, "heat fouling" the spark plugs, or anything else out of the ordinary, there isn't a problem. It's nice when everything runs according to the books, but like you say, this thing is 22 years old. Things are bound to run a tad bit different than when it was brand new.
I'm still leaning towards a water pump though...and that's because you can smell antifreeze but can't find it. Take the belts off and try to wiggle the water pump pulley itself. If you get ANY movement, it's bad or at least it's on it's way out.



> This is what the FSM says about the thermo switch:


I stand corrected or rather more informed...



> No idea if the timing chain has upper guides, this is what the FSM shows:


Wrong pic to see the upper guides and tensioner.


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## ahardb0dy (Nov 9, 2003)

I'm going to order a new water pump next Wednesday, When it gets here I plan on flushing the system out again, than I'll remove the old pump clean the area real good, compare the old vs the new pump, take some pics of it. and install the new pump. I'll let it sit over night than fill with distilled water and run the engine to check for leaks, if no leaks I'll drain some of the distilled water and than add antifreeze. Will see what happens after that.

Today going to bring the engine up to operating temp and take some temp readings at he different sender locations with the infrared thermometer I borrowed to see what the differences are. Will post back results.


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## jdg (Aug 27, 2009)

Did you pull the belts and wiggle the water pump pulley itself?
I think in this case, that'll tell you a lot more than spending the time warming it up and taking temp readings, etc.


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## ahardb0dy (Nov 9, 2003)

No not yet, I think I'm going to replace the pump either way, it is 22 years old and I can imagine what the impeller looks like.

The temp readings are just to see how much, if any difference there is between the stck sender and the autometer sender locations.


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## jdg (Aug 27, 2009)

Pump pulley wiggle = 99% chance it's bad
Pump no wiggle = meh...might be good, might be bad, call it 50/50.


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## ahardb0dy (Nov 9, 2003)

even if there is no play in the shaft the impeller could still be shot, for the cost of a new water pump ($22 delivered from Rockauto.com) I'll replace it and know it is good. Like you said previously the amount of crap that could be on the impeller from running straight water through the engine, I'd be lucky if their was anything left of the impeller !! LOL


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## jdg (Aug 27, 2009)

ahardb0dy said:


> I'd be lucky if their was anything left of the impeller !! LOL


Just so happens I helped a friend with a 99 F150 5.4L with an overheat problem a couple weeks ago. Took out the water pump and ALL of the impeller blades were actually missing! All that was left of the water pump was a spinning disc. Don't know where those blade went but they are stuck somewhere in the block. We put a borescope down in there to check every passage and couldn't find the bits/pieces. Thinking maybe they shelled themselves to bits somehow. Anywho...engine is running fine now.
Weird stuff...


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## ahardb0dy (Nov 9, 2003)

Pulled the belt off few minutes ago, not a lot of play in the pulley/shaft, I mean I had to really try to make it move to get it to move, pulley spins smoothly but seems like it has some resistance on it.

Took temps at the water outlet and the thermostat housing, the water outlet was hotter of course, the infrared thermometer was reading almost 20 degrees higher than at the thermostat housing.

Also think I solved my problem of the RPM's dropping when I come to a stop and put the clutch in, I adjusted the dash pot to factory specs, took it for a test drive and when I put the clutch in and stopped the rpm's never dropped below 850.


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## jdg (Aug 27, 2009)

Well, if the pulley doesn't move side-to-side, then, in my mind, kinda rules it out, and the fact that it still has a bit of drag when you try to spin it also says that the seals are still 'sealing'. But...as you said before, it's 22 years old.


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## ahardb0dy (Nov 9, 2003)

I'm still going to order a new water pump on Wednesday. Any tips on replacing it?


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## jdg (Aug 27, 2009)

Not really. Don't own a '90 and never looked under the hood of one.
If it's like my B14's (doubt it, but ya never know), about the only thing I can think of it to move the P/S hose bracket on the right strut tower which will give you a bit more room in there to loosen up the P/S pump and get that belt off. Maybe pull the upper/right motor mount (support the engine with a block of wood on a jack under the oil pan)...might give you a bunch more elbow room to play around in there.


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## ahardb0dy (Nov 9, 2003)

what's P/S? Just kidding, I don't have power steering so I only have to pull the one belt, have the AC belt off already as the compressor is shot and was making noise, was thinking the same thing about removing that upper engine mount just to get more room.


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## jdg (Aug 27, 2009)

And there ya go...proof POSITIVE I've never looked under the hood of a '90 Sentra.

Guess you don't have to worry much about resetting the DVD/NAV/Infotainment system settings after disconnecting the battery eh?


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## ahardb0dy (Nov 9, 2003)

I just looked up the water pump for the B14 1.6 on rockauto and some of the pics look the same as my water pump and a few look different, maybe they messed up. I thought the block was supposed to be the same between the GA16i and the GA16DE.

here's an under hood pic of my 90:


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## ahardb0dy (Nov 9, 2003)

Today the new water pump was delivered. I ordered one made by Beck Arnley, it is new. I pulled the old water pump and than pulled the thermostat housing, cleaned the thermostat housing really good. I think because the water pump has 2 gaskets, one goes to the thermostat housing than one goes between the water pump and the front cover, that I'm going to bolt the new water pump to the thermostat housing first, letting that connection dry good, than bolt the whole assembly to the front cover. At least this way I will know I have a good seal between the thermostat housing and the water pump.

I took pics of the old pump and the new one, the old one the impeller didn't look too bad, it looks different than the new one.

here are the pics of the old water pump and the new one:


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## jdg (Aug 27, 2009)

At first glance, the old one doesn't look too bad......except for that rust color on the impeller blades. That tells me the rest of the innards of the water jackets in your engine are probably covered in the same muck.
Also, the outer edge of the impeller, where it might ride up against the inside of the timing cover looks like it might've scraped a bit over the years.
meh...overall the old one is probably done for. Hope it fixes the problem...if there actually is a problem, which is kinda my first contention...


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## ahardb0dy (Nov 9, 2003)

So today installed the new water pump, filled it with filtered water for now, ran it checked for leaks, none found. Topped it off, bled the air out, topped it off. Let it run to see if the fan comes on, it did at 209 on the auto meter gauge. Took it for a spirited ride, back home, checked again for leaks, none found. Temp was running about 180 while driving. Will keep an eye on it, have to get some straight anti freeze tomorrow, than will drain some water out and add the anti freeze.


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## jdg (Aug 27, 2009)

Info you...water is a much worse coolant than antifreeze/water mix, not just because of the rusting factor, but because of the heat capacity of water vs antifreeze/water.
You might find the engine running even a bit cooler when you get the antifreeze mixed in there.
Nonetheless, at least now you know you got a good water pump and it sounds like you're back in business...


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## ahardb0dy (Nov 9, 2003)

I thought the antifreeze/water would cool better but wasn't sure. Actually was going to look it up in a minute. Thanks.


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## ahardb0dy (Nov 9, 2003)

antifreeze is in, was at Ace Hardware yesterday, found full strength antifreeze gallon on sale for $8.99. Will be driving the car this week, will see how it is. No AC but uses less gas than the pathfinder.


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## ahardb0dy (Nov 9, 2003)

Update, had to order 2 hoses from the dealer, no one local had them, installed the hoses today, topped off the water, bled out any air, let it warm up until the fan came on, no leaks, fan still coming on right at 209 degrees on the Autometer gauge.

Remembered I picked up a thermo switch out of a clean 90 sentra at the junkyard 2 weeks ago, so I removed the aftermarket one and installed the used thermo switch, topped off the water again, let it run, fan came on right at 199 on the autometer gauge. Let it run and watched the temp gauge and every time it came on at exactly 199 degrees. So I guess even though the aftermarket thermo switch is supposed to turn the fan on at the same temp as the OEM part it isn't.

Have to wait for someone to come over to pick up an old tv than will take it for a test drive, recheck for leaks and if none should be good to go !!


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## heatherL1973 (Feb 25, 2014)

*water gsuge drops*

Hi I just bought a 2000 Nissan Altima.
I have only had the car for a few days, and I just noticed that the water gauge warms up fine , but while driving it keeps dropping to cold.
even after driving the car for 30 minutes or more on the highway at 65-70 miles per hour...a few times it almost dropped all the way to cold.
anyone know y? Or can give me some advice?

the car dealer did inform me that they put a brand new radiator , because there was a hole in the old radiator. They also put a new valve cover , and sepertene belt.

thank you heather


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## ahardb0dy (Nov 9, 2003)

I would check the connection to the temp. sender first, make sure it is a tight connection, and there is not any corrosion on it. If that is not the problem it may be the sender itself, there should be two, one for the gauge that looks like this one:

More Information for AIRTEX / WELLS 1T1154

and one for the ECU, the ECU one would look like this:

More Information for STANDARD MOTOR PRODUCTS TX78T

this is where the sender for the gauge should be located, see red arrow:


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