Gen 3 overheating issue, or is it?

Hi all,

I have spent many an hour reading the other posts and threads on the forum here and I want to run my issue past you all to see what people think on my issue. Bit of a long one to give all the details, so apologies. 

Gen 3 jimny 2003 manual, new to me around 2 months back or so, coming out of spring into summer here in Australia. I am located Gold Coast, QLD, so sub tropics and recently been having 32-39C day temps. Short drives of about 5-7kms in length, car gets up to temp, has normal power behaves like there are no issues, temps and everything seem fine.

However, longer trips or when caught in very heavy traffic the temp gauge creeps up very high. I haven't let it go all the way to the top. When the gauge goes up and I am at a standstill, bringing the revs up to 2-2.5krpm is enough to see the gauge drop.

The fan was already on its way out when I got it, so I put a new viscous unit in, I have also replaced the radiator as it was a bit crusty and didn't seem like it was flowing that well, replaced the water pump and thermostat (though no genuine ones where available and the housing now has a tiny pin hole leak (loses maybe half a teaspoon on a long trip,I can see it build up on top of the thermostat cover and then dry out over a longer trip), so this will be replaced again shortly, but its bled and flushed and everything seems great and that will be addressed very soon. 

However the temp gauge is still going up on the longer drives even on a particularly cool night we just had when I was going to work. Raining, cool temp of about 18C and the temp gauge went up high when stopped at the lights.

Now the engine heater pipes seem normal. Top hose is hot, bottom hose cooler after the radiator and fan do its job. The two bulk head hoses into the heater matrix get nice and warm, and I have good heat out the vents in the car if I put the heater on. It seems like it was bled well. No coolant loss (besides not even a dribble at the thermostat cap while I wait for a new factory one), no issues at all. Nothing to indicate any issue whatsoever, other than the gauge going high.

Here is the interesting bit I found. The other night on the rainy, cool night, I had to put my window down to access my parking at work. When I ran the window back up and the temp gauge was up, I held onto the window switch a little longer after the glass was all the way up, and the lights dipped a little, like when you have those electrical loads creep up. At the same time, I visibly saw my dash temp gauge drop right on back to normal operating temp level while the window switch was on.

As soon as I let off the switch and the electrical load went back to normal, the temp gauge crept back up to hot. This had me intrigued, because I can replicate this every single time the temp has risen over "normal levels" with the window switch, or all the lights and electricals on to add that heavy load.

Thinking about other issues and how it seems like an electrical sensor, I remember that there is the common thing of the sensor in these jimny's for the crank angle I think it is that overheats, and if you add water onto it and the car runs better, you know the sensor is the issue.

Tried that with the Engine Coolant Sensor ( ECT Sensor )   and wouldn't you know, the temp gauge drops right on back to the normal level of midway on the gauge and stays there a little bit until the water has evaporated off the ECT sensor and everything is warming up again.

I have placed an order for a new ECT and its on its way, as my local suzuki dealer is hopeless for carrying parts, but has anyone seen of or heard of something similar?

Thinking about the location of the sensory, it is right at the back of the head against the firewall, the exhaust manifold looks to be aftermarket and has no shielding. I am wondering if in slow traffic/at a standstill, the air temp is heating up there above the exhaust and that sensor is struggling with the heat causing electrical issues?

Looking to do something on the manifold to coat it now and cool it down a little and maybe find a heat shield, but could I be on the right track here that this isn't a cooling system issue now that everything other than the thermostat cap and the ECT sensor are brand new, working well and handling things in every other way?

How about you get an IR temperature gun (they're not expensive) and let's find out if there really is an overheating issue.

That header also doesn't look stock, I wonder if that, or the missing heat shield has anything to do with it.

Just picking up on a couple of things you mentioned:

- the temperature gauge goes back to normal when you raise the revs;

- the temperature gauge goes back to normal when you hold the window switch on and the headlights dip.

Just an alternative idea, when you raise the revs, you also increase the alternator charge and hence battery voltage. Driving the windows changes the load and hence the battery voltage as well.

A lot of sensors are voltage dependent, normally not a problem as the voltage is regulated, but if you have a weak battery, alternator or faulty voltage regulator you can get some weird things happening.

I agree with Fordem, get an independent temperature gauge and check that the engine is not over-heating even when the gauge says it is and then if the engine is OK look for an electrical fault (possibly battery, alternator or regulator).

Thanks everyone. I am getting my hands on an IR gun over the weekend to check exactly this as well.

But yes, I am very much thinking the heat from the headers could be an issue.

I am also wondering if there is aa voltage issue. Bringing home some of my test tools tonight to try and check that a bit further too.