erratic temp.

[Oz2]

Went out for a drive this morning, not a very hot day but the temp gauge was up and down between normal and just under the red......Did'nt seem to make a difference as to my speed but it seemed to to fluctuate at higher temps toword the end of the trips (1/2 hour each way). Had a read through the bible and there seemed to be a lot of slack in the fan belt (alt/water pump etc. belt) which I have since tightened but have not tested it yet as it is 11:46pm here now....any thoughts?
many thanks

Adam

[mrzigazaga]

Hi Mate..Mine reads 280 all the time in the 280..(The irony) but that was after i had the system flushed and refilled with new coolant..I put a new sensor in but was told by Dan taylor that you have to match the gauges up with the sensor...I used a probe thermometer that can withstand high temperatures and whilst it was reading 280 i took a reading..The thermometer read 180..Its worth checking..Could be a sensor on its way out..Thermostat sticking?..Any leaks?..Air in the system..Faulty gauge..Blockage somewhere?..Hope its something simple..Ziga

[grahamw48]

Sometimes it's better when gauges DON'T work.

You can enjoy the driving without nervously scanning them the whole time.

[jeff m]

grahamw48 said:

Sometimes it's better when gauges DON'T work.

You can enjoy the driving without nervously scanning them the whole time.

So true

If your gauge is fluctuating quickly, it is probably just the gauge, sensor or a ground.

If it is creeping up even though you are driving at a decent rate of knots, get somebody to check it with a pump. They'll pump it up to 15psi and you will see what is happening. (leaking, loosing pressure etc.)

Or..... buy two new caps and see if there is any improvment.

[jmorgan]

400? Airlocks could be an issue, tend to crop up after fettling the cooling system. I found the loop through the bulkhead to be quite high. Also, all caps sealing OK? Swan neck and pressure cap that is.

[dixiebabes]

Yup airlocks can be a problem just changed my coolant again drained and blew it all out. filled it right up to top on swan neck took it for a drive and experienced all the symptoms you are having Adam. when i got home added another say litre and half so they do need bleeding. But if you aint touched the coolant probably will be a dicky earth or sensor.

Dix

[jmorgan]

Changed a few pipes recently and back filled it up through the heater.

[E Ponym]

If you refit the thermostat you will need to ensure that the jiggle pin hole is at the top.

The jiggle pin is a little loose part in a hole through the static disk of the thermostat, it ensures that there is a path out for air before the thermostat opens. If the jiggle pin hole is at the bottom then there can be a pocket of air (rather than water) around the thermostat bulb during initial warm-up and this can cause late opening of the thermostat and can fool people into thinking there is a blown gasket.

The symptoms usually cure themselves after the first couple of warm-cool cycles but if you have a leak then more air can be introduced.

Have you had the thermostat out recently?

[Oz2]

Ok, I've just run the sx up from cold having tightened the fan belt, holding on to the rad inlet pipe (swan neck) the engine was warming up while the swan neck remained cold, according to the temp gauge the therm opened above 90 but before the red, the fans came on and the needle came down to norm and remained there, all of this was on idle...Maybe a lower temp thermostat is the go, the temp has been a little bit erratic since the car has been here in Australia so perhaps the fan belt has been getting worse, I've not heard it slipping though! It does'nt loose water or boil up (the needle has never gone into the red),when I drove it Saturday once I had stoped, the expansion tank was hot, tonight once it had stoped the expansion tank was slightly warm i removed the cap and felt the water and it was the same, so was the bottom hose off the rad, this could be due to the bonnet being open...... I did at one point think while I was driving that the volts were low, tonight the volts seemed ok this could also point to the fan belt..hopefully all i need is a new fan belt:-)
Thanks for all the help so far I'll keep doing one thing at a time and test so I know what the prob was...

any thoughts on this

Thanks Adam

oh yes and i have ordered one of these as a back up temp guage I thought it looked good, the 4x4 guys use them here in Australia, check it out let me know your thoughts....http://www.sig.itel.net/

Edited by Oz2 on Monday 28th March 12:32

[Oz2]

does your temp gauge go a little high and then settle to its running temp?
and what rating is your thermostat SH bible says the 350 had a 88deg as standard and some larger engines have as low as 75 the SX would run hotter because of the compressed air maybe I should run it without a thermostat to see where it sits and then asses if i should fit a cooler one????

Adam

[Number 7]

I alternate between an 82 deg for most of the year except for a couple of months in Summer (England!) when I use a 74 deg. You can run an engine too cool though. I don't think the Lucas ECU chops the warm-up routine until something like 80 deg. C.

[Oz2]

HI All,

I have fitted the "engine watchdog"
http://www.sig.itel.net/
The block temp is 74-76 driving and 83-84 in traffic, the water temp (on the gauge) still rises and falls (but not as bad since i tightened the fan belt) I think my next step is a 74deg C thermostat.........can anyone tell me the measurments/spec of the thermostat '89 350sx....
How do you know if you have air in the heater section of the cooling system, I did run it for a while with the swan neck cap and expantion tank cap off, would this not get rid of any air?

Thanks

Adam

Edited by Oz2 on Saturday 2nd April 12:12

[jmorgan]

I fitted some temperature tell tales on the go and return for the rad. Sticky tabs that showed the max temp reached, the bottom one fell off but the top one never went above 80. Think the bottom was on 60? I do not know how accurate the sticker were but it was a confidence boost when I thought there were problems and they were only a few quid and seemed to indicate the gauge was in the right ball park.

Heater and air locks. Cold out the heater is a good clue...... But if your valve is open, the go and return pipes hot, I would think there is not a lot if any air in there? On mine I feel the pipes at the bulkhead, on the 400 they are easy to get at for a fell under the dash as well. I also fitted a bleed valve to help the issue but it is not a must.

[Oz2]

went out for a run this morning and it seems to be setteling down, it's good to have a second gauge it's a very accurate gauge of the block temp (fans come on at 81)I will test to see what temp the thermostat opens. well worth the $150 (about 90GBP)

[Oz2]

thought I'd better reply with the latest........went out for a run today and stoped in at my workshop to have a look at the cooling system, on the way there the temp had been up and down as usual, must be an air lock?????? therm opens at 84,fans come on at 81, pumps pumping, fan belt at the right tension and there is water in it, completely.........
So, removed the swan neck cap, removed the expansion tank cap and let it run for about 5min's then the water started overflowing at the swan neck so I let it until it stoped overflowing then i replaced the cap, the water level had reduced in the expansion tank (before, if i inserted my middle finger INTO THE EXPANSION TANK THAT IS!!!! I could just touch the water) but now it is much lower and has revealed what looks like a level indicator, so I put the cap back on and off i went for about a 40 minuite drive, back roads, main roads, open road and in traffic, hillclimbe with hairpins, fanging it and cruising and to finish about 90mph down the freeway. And.........ALL GOOD!!!!
I don't think any air came out I think it was all down to there being too much water in the system, Is this a possibility????

highly recommend the engine watchdog great device for a reassuring back up to the temp gauge accurate engine block temp every 2 sec, mine is hardwired in and it sits under the battery box in the foot well so it not visible but i can see it when im driving.

Thanks All

Adam

[mrzigazaga]

Hi Mate..It does depend wether your expansion tank has a pressurised cap which it should if your rad dont..That should let any excess water out..Have you run the car up to normal temperature with the heater on hot and turned on?..It could have an air lock in the matrix side of things and if your fan is coming on and going off it would suggest no air lock or blockage..With my 280 i had to put an old expansion tank in as a catch tank as i had a leak on one of the core plugs but if your water when hot is being pushed up and out that could suggest air in the system somewhere..Hope this helps..Ziga

[Oz2]

I'm sure there is no air lock now, it does have a pressure cap maybe it needs to be lower.but the temp sits well now slightly above 90 on the gauge and 74-76deg driving and 80-86max in trafficon the watchdog.

[grahamw48]

That sounds about right to me.