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Post by ellisr on Sept 18, 2008 21:26:48 GMT 11
Hi - has anyone found available or installed a thermostat with lower opening temp than the standard 82 deg C ??
My 97 Bighorn (4JG2) when going up long hills and obviously pushing more fuel through will raise temp needle on gauge from normal centre of cold and hot to around 3/4 towards hot. It will suddenly go straight down to the normal 1/2 way point just like that as if the thermostat has suddenly opened fully. I put in another new hi flow thermostat thinking the other one may have been sticking but no difference at all.
Vehicle has only 40000km and when you look in towards head when thermostat removed its just like a brand new motor - same with radiator so no chance of sludge/corrosion etc.
So back to original question, would putting in a thermostat with lower opening temp be of any value ??
Cheers Richard
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Post by geeves on Sept 19, 2008 7:42:31 GMT 11
Very low milage engines are more likly to have internal blockages than higher milage vehicles as they sit more and the coolent is much older once it gets to its change milage. I would get the radiator checked out even if it looks new on the outside. Anouther common failure is the fan which will cause low speed overheating but not at open road speeds.
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Post by geeves on Sept 19, 2008 7:43:53 GMT 11
Also if its auto a fault in the auto can cause overheating. The thermostat opens slowly over a range of temp but 3/4 up the guage is way higher than this
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Post by ellisr on Sept 19, 2008 9:46:07 GMT 11
Thanks for the advice.
The radiator is definately a good one as already been checked. Auto recently serviced and was told its a beauty !! As for the viscous fan, how do you check this ?? ........the thing i cant figure out is the sudden speed at which the temp gauge goes from 3/4 back down to 1/2 as previously mentioned like the thermostat is suddenly going to fully open with corresponding full coolant flow.
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Post by geeves on Sept 19, 2008 12:01:58 GMT 11
Ive had that one time before on an escort I used to own. Does this happen within the first 20km of a trip or every time you see a hill? The old escort had a leaky head and bubbles collected under the thermostat insulating it. 5km out of Rotorua it boiled but the water in the radiator was cold. Thermostat out on the side of the road then drove back to Wellington to flush the system as the water used came from a stream called kerosene creek which doesnt smell very nice and is hot already.
To test the fan try and turn when cold and note the resistance. Then do the same with the engine fully hot (engine off or you lose fingers) It should be the same or harder to turn. Mine was fine except in slow off road climbs where the guage would hit the red. In that situation the fan would spin freely although any other time it was fine. Fan from wreckers and problem gone
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Post by isuzumudman on Sept 19, 2008 21:15:00 GMT 11
I'll second what Geeves says about the viscous fan. Last summer a friend purchased 2 fans from R..CO during a trip around the South Island and we only proved both to be bad when I swapped mine with his. R..CO staff tried to suggest that freewheeling when hot was a design feature. Bul.Sh.t. If the fan free wheels when hot it is stuffed!! End of story.
As far as the thermostat is concerened, the only way to check it properly is to remove it and put it in a pot on the stove. If you have a thermometer so much the better. However, the thermostat should open fully well before boiling point. It doesn't matter so much when it closes.
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Post by geeves on Sept 20, 2008 9:41:41 GMT 11
Another test would be to run for a few days without the thermostat. Not good for power or economy so dont for too long. If it still overheats the problem aint the thermostat. Also Im a little suspicious of the isuzu temp gauge. When it is hot try dabbing a wet finger on the top of the radiator and the thermostat housing. Expect a very minor burn from this so dont hold it there just touch and go. If the water stays several seconds before evaporating its the nature of your gauge but if it boils almost instantly you have an overheating problem
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Post by ellisr on Sept 24, 2008 15:20:34 GMT 11
Im going to rig up some sort of digital temp sensor or thermocouple and attach to thermostat housing to hopefully get the real temperature (rather then the temp gauge on dash)
As for my viscous fan, it has quite a bit of resistance when engine is cold and when hot the resistance is still there but definately not quite as much ?? .......had bonnet open and was watching fan blades at idle then with outstretched arm reached to key and turned off motor - the fan blades stopped straight away both when cold and hot so i presume the fan clutch is engaged, it certainly didnt free-spin.
Did some reading on Google and came across articles that said viscous fans are usually quite stiff when cold because of the fluid that is sitting at the bottom - thats why there is lots of fan noise for the first 30 secs or so from cold. Does all this sound right ?? Does my fan sound like its working correctly ??
Cheers
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Post by geeves on Sept 24, 2008 16:06:31 GMT 11
The clutch should be full of a silicon based fluid with quite unusual properties. It actualy gets thicker as it gets hotter. Cold it could be quite stiff then as normal temp is reached stay much the same but once it gets very hot it should stiffen up so it can push more air. Never heard of them being noisy cold before.
Even so at speeds above 50kph airflow should be enough to cool the system even without a fan. Sudden changes of temp suggest something else is going on. My money is on either a loose connection to the temp gauge or sender, or a leaky head causing bubbles to insulate the thermostat.
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