Hi F,
my educated guess is that the thermostat is stuck OPEN.
That will cause the engine to use COLD coolant from start up.
The temp. gauge reads from the ENGINE side of the thermostat so it is
highly likely that it will fluctuate as the engine momentarily heats
the coolant.
Better than being stuck closed, BUT, still requiring to be changed:-)
Regards,
Graeme Suckling
http://tinyurl.com/6n5aza
Adelaide
South Australia.
On 8/01/2013 3:15 AM, O'Farrell, Fergus P (AS) wrote:
> Trying to help out a family friend to whom I owe numerous favors.
> Rode in his ~86 Pathfinder (VG30E/5spd) admittedly in freezing weather
> (10-20F), and it seemed to me that the thermostat has gone wonky, but need
> critique of the diagnosis.
>
> On start-up the temp gauge stays on dead cold, for quite a while (longer than
> it should), defroster blows cold, so it is truly cold.
> Then the begins to rise, and then cycles up/down with the engine speed, (mind
> you we only got up to 25-35mph, but it was ~15 degreesF) as if the revving is
> injecting heat, but the temp gauge is responding almost as quickly as the
> tach. (possible parallel elec issue?) Starts to blow slightly warmer air out
> of the defroster, but never really gets HOT.
>
> I am thinking the thermostat is getting crusty/clogged, so is slow to respond
> initially, then is snapping open and staying crustily stuck in that position.
> (but wouldn't the temp gauge be reading radiator output water temp, and thus
> be reacting somewhat slowly to engine revs, not reading radiator input water
> temp and thus reacting quickly to heat inputs?)
>
> Perplexed, and trying to pass on good advice before someone digs in to an
> "dry, as yet undisturbed, but with 130k+ miles" engine.
>
> Thanks, and happy holidays,
> Fergus O
> (thankfully back to a warmer climate)
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