My 2000 Pulsar (QG16DE engine) went into the red on the temp guage today, thought it could be bad thermostat, as the top hose was hot, but bottom cold. Took thermostat out and its still doing it! What could the other cause of this be! Thought waterpump, but this is a resonably rare thing to fail! Always been well serviced, full of antifreeze, always ran at half on the temp guage. Guage goes from hot to half and vice versa quickly. Any ideas! Possibly waterpump or blocked radiator! Looks immaculate and clean inside from where the cap attaches though. Would a cracked head or blown headgasket cause the hot top hose/cold bottom hose scenario! Cheers
ambo11,
Apr 23, 3:17am
Forgot to add oil is golden and clean and antifreeze/radiator coolant is still the Nissan blue colour.
toyboy3,
Apr 23, 3:31am
impeller fallen off water pump!if top hose hot bottom hose cold
henderson_guy,
Apr 23, 3:46am
agreed, either water pump or blocked radiator. I would personally do the radiator first, about $90 to get it rodded out if you can remove it yourself.
johnf_456,
Apr 23, 4:20am
Water pump or blocked rad
ambo11,
Apr 23, 4:21am
Thanks for that, yes, can remove radiator myself easily enough.cheers.
intrade,
Apr 23, 3:38pm
is your internal heater giving off any heat at all ! if not then your waterpump impeller is not turning or is desintigrated. if it gets real hot inside then impeller works fine radiator unblock. and fan cooling switch check. like my fiat would always cool at 90 degree in a traffic jam only and then a few month ago it went to almost 100 just up a hill and fan would hardly spin on radiator. turned out it has a dual stage thermal switch 84 to 90 degree cooling and 90 to 98 secound stage. the first stage musta have failed years ago and the secound was to die also when i found the problem.
therafter1,
Apr 23, 3:56pm
I personally wouldn't take the thermostat out of the equation that quickly, if you have simply removed the thermostat and put it into a pot or jug and boiled it and it has opened doesn't necessarily mean that it is opening and closing at the correct temps in the engine.
The vehicle sounds well serviced so it strikes me as odd that the radiator would go from being clear to blocked in such a short time frame, particularly in the cooler ambient temps that we now have.
Impellor failure on water pumps in well maintained systems isn't that common in my experience.
For the price of a replacement thermostat I would replace it. Nissans seem to have a tendency to prefer OE thermostats.
intrade,
Apr 23, 4:07pm
therafter1 he posted it aso happened without the thermostat.
therafter1,
Apr 23, 4:21pm
So he did !
Is it the double acting type thermostat, in which case it will still probably over heat.
ambo11,
Apr 23, 8:07pm
Thanks guys, looking at waterpump will be next step.Flushed system completely with just fresh water, the second I put water in the top of radiator it immediately comes out the bottom.and car is well serviced so I too doubt the radiator would be that badly blocked that quickly. Antifreeze was genuine Nissan,and from what I can see of the internals of the radiator it was clean alloy. Yep last night when I spotted the temp guage I quickly turned heater onto Hot, but it only blew cold air. Started it today and it warmed up, sat at normal temp and blew hot air with heater. Tried again just now after it cooling right down and once again bottom hose cold, top hot, no thermostat in, and severe bubbling in overflow bottle. So I wont touch it again in case its salvageable, I'm guessing waterpump too.unless it has cracked the head.would that cause top hot, bottom cold, with the radiator hoses!
therafter1,
Apr 23, 8:21pm
I do not re-collect whether or not these engines have double actuation type thermostats in them. If it does have a double actuation thermostat in it then the cooling system will be completely out of whack without it, so before I went after water pumps and cracked head/blown head gasket type scenarios I would replace the thermostat with an OE thermostat and fill and bleed the cooling system again and go from there.
You do not have to fill and waste coolant during this process just use good clean water, once the problem has been solved drain the water and re-add the correct quantity of coolant.
Try the cheap and simple things first.
scoobeey,
Apr 23, 9:42pm
My van overheated up hill was blocked radiator ;man said was 20 percent blocked made a hell of a difference!
ambo11,
Dec 5, 6:53am
Yeah the thermostat is quite large and has Nissan stamped on it, so guess I better go for original Nissan. Thermostat rubber looks buggered and the brass is worn down one side where its been rubbing, so its rubbish now.No leaks from waterpump, slight resistance when I turn it by hand, and when I rev the engine the pressure in the hoses increases, which I've heard is a redneck way of testing if the pump is pumping.topped it up (trying to bleed it correctly) and went for a 15 minute round town drive and its sitting exactly where it used to on the guage, and radiator and hosesare not overly hot to touch straight after.heres hoping it just needed a decent bleed in the cooling system. Will try it for a few days before I spend money on a genuine Nissan themostat. Cheers for the replies.
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