temp guage trust issues

[ezytiger83]

since putting a 3 core rad and thermo fans in the MU, i may, or may not be having temperature issues. i decided to go with an adjustable fan control with a bulb inside the top radiator hose, a digital temp gauge sensor is in the same spot and the factory temp gauge hasn't been touched.

set the fan switch to 40'c and went for a drive to get the fans to trigger so i know it's working. After an hour of driving the digital gauge hadn't shown more than 20'c, and the factory gauge was in the 1st quarter. i stopped in my driveway to try and get some temperature without wind passing thru the rad and managed to get the temp to rise and the fans to trigger, so now i know that the fans are wired correctly and i get the digi gauge and the fan switch both registering 40'c in the top hose.

BUT, the factory gauge hits halfway when the digi gauge reads 30'c and then hits 3/4 or more when the digi gauge hits 40'c and the fans kick in. Who do i trust? no warning lights came on either.

could this indicate that there's a blockage in the cooling system, and how can i check this? the top hose is firm with the engine running, so can i assume the water pump is fine?

when i first installed the digi gauge with the standard radiator, i hit 120'c + (i'm guessing the digi gauge maxed out) which is why i've made the switch to the larger radiator. i plan to keep the standard fan as a safety, if the electric ones fail for any reason, i can remove the shroud and bolt the old fan back on.

Hope someone can help, i could use the peace of mind.

[geeves]

The thermostat is inbetween your 2 guages and might be the cause but my money is on a poor earth on the digi guage.
A finger test might show the answer. take the cap off and stick your finger in the water If it feels like bathwater its around 35C If it feels hotter than you like your bath but you can hold your finger in its 50ish If you have to take your finger out straight away its above 55 if the skin falls off its more.
I just looked up todays weather in Perth and it was 27 so a temp of 20 in a running engine has to be a lie

[ezytiger83]

roger that, i'll check the gauge tomorrow, def think the earth may well be the problem, having just returned from a short drive to find the fans on, but the gauge hadn't registered.

the biggest issue earlier was that i had 2 aftermarket readings of 40' to 1 isuzu reading of overheating, lesson learned; never doubt the isuzu!

not sure why the factory gauge got so high earlier tho, i'll be adjusting the fan switch to come on at a higher temp tomorrow, but i'll still keep monitoring, will have to get the mechanic to double check everything for me at the next service too.

[mattmannz]

I fitted a quality aftermarket temp guage with a sensor in the top radiator hose. As the sensor is after the thermostat it takes a while for the gauge to register as until water flows through the thermostat there is nothing to read.

My truck with new radiator, coolant, hoses, thermostat and cap runs between 80 and 90 depending on what I am doing. Still has the stock fan but no shroud. The stock gauge runs about 1/3 at 80c and almost no noticable change for 90, it's still under half at that stage.

Haven't been able to get over 90c yet so not sure what the temperature would be with the factory gauge in the red!

Matt.

[kcsoft]

Haven't been able to get over 90c yet so not sure what the temperature would be with the factory gauge in the red!

red=fkin hot... meltdown time, a chernobyl level event from my experience with petrol engines. i'd like to think the diesels are a bit tougher.

[diesel]

Haven't been able to get over 90c yet so not sure what the temperature would be with the factory gauge in the red!

red=fkin hot... meltdown time, a chernobyl level event from my experience with petrol engines. i'd like to think the diesels are a bit tougher.

they are slightly tougher all-round but your block will more than likely be warped and need to be machined or lots of gasket seal either way your engine will never be the same

[geeves]

Please dont say that. I had my fan on a feed that was only live when charging. Alternator died in a river ($500 for a new one) followed by a 400 meter vertical slow off road climb. Temp guage was right at the edge of the red and took a long time to come back.
No steam so it didnt boil.

[ezytiger83]

i'm still sorting out that gauge issue, have to make a slightly longer wire from the gauge adaptor in the top hose. i just had it running thru some corrugated tube under the intake hose to the inlet manifold on the enginge. i think the engine vibrations tore it loose, but it stayed hidden within the tubing...

[ezytiger83]

the earth wire, i mean

[mattmannz]

If its a two wire sensor it probably doesn't need an earth.

[ezytiger83]

well it's one thing after another, gauge works now, but the fans don't...i must have angered the isuzu gods...

[Captcol]

Quick stand clear, he has angered the isuzu gods, let him not touch us or our vehicle lest he ..... ah screw it, unlucky dude, work your way through it will probably be a loose terminal or a internal cable break ... maybe

[ezytiger83]

more trouble than it's worth, i'm gonna get a professional to find out what's happening. the radiator swap is a good idea, but adding electric fans has driven me insane. everyday something new stops working. i might do away with the adjustable switch as it's been the cause of the latest dramas. will hopefully be able to run the fans using the standard isuzu stuff.

[ezytiger83]

update: i wanted to try a new relay before i took it to an electrician, supercheap had spotlight harnesses for the same price as a single relay, so i decided to replace all the wiring one last time and use all new earth points and a new switch. it looks neater now, but i've only managed to get back to where i was before all the glitches began.

the problem is the fan switch, you can see on top of the rad hose, it's a pro comp unit, but looks similar to the ones from davies craig. with no wires attached, you can turn the dial and hear an audible tick at the temp of the coolant, but if i connect the wires (which interupt the switched 12v to the relay) it only operates at the base temp of 40'c. i've tried switching the spade connections in case it's in/out sensitive, but it's exactly the same.

i'm watching the temp gauge and turning it on manually for now, but i can do that without the thermo switch. so any ideas??

[mattmannz]

Do you have a wiring diagram for the fans/relay and the thermo switch?

The best way to wire it up is to use a thermo switch with a normally closed relay so that the thermo switch opens the relay when it's cold thereby stopping the fans from working and has it heats up it lets the relay close thereby activating the fans. This way if the thermo switch fails the relay runs them all the time.

The fans are usually postive switched through the relay so a large always on battery feed to the relay then to the fan and a large earth from the fans to the body. The relay will need a low amp positive on the switching side and the feed from the thermo switch.

How do you know it's only 40c?

Cheers
Matt.