Advice on Temp Gauge fluctuation on 90 hilux

Submitted: Saturday, Mar 02, 2013 at 10:00
ThreadID: 100847 Views:3834 Replies:4 FollowUps:8
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I have a Toyota with a 2.8D motor, recently I had to replace the water pump and all went well for a few weeks.

Recently the temp gauge needle started jumping up and down, very fast from mid range to low range, the needle was almost dancing up and down.

I checked the coolant level and all seemed ok, the wiring looks ok from the thermostat.

Was thinking of just removing the thermostat and moving on.

Any ideas out there....
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Reply By: Member - Bruce C (NSW) - Saturday, Mar 02, 2013 at 10:46

Saturday, Mar 02, 2013 at 10:46
Hi 4Runner,

Sounds like a bad connection to me. Look for a broken wire inside the insulation at the temp sender. Leave the thermostat in place or at least renew it as it is most important in diesels to get them up to operating temp quickly.

Even if the water temp was fluctuating the needle would not be moving as fast as you describe. Check for broken wires and bad connections.

Could also be a faulty sender or gauge.

Cheers, Bruce.
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Follow Up By: olcoolone - Saturday, Mar 02, 2013 at 10:48

Saturday, Mar 02, 2013 at 10:48
x 2........
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Reply By: Bushranger1 - Saturday, Mar 02, 2013 at 10:52

Saturday, Mar 02, 2013 at 10:52
G'day,
By all means change the thermostat but don't run the engine without one.

Modern vehicles are designed to get to a set temperature quickly & maintain that temp as governed by the thermostat. Your emissions & fuel consumption will increase if the engine overcools by not having a thermostat fitted. You will also get internal condensation in the engine in cool weather.

Best to purchase the correct OME one as well.

Some people say that not having a thermostat fitted will cause overheating due to the circulation of the coolant being to quick through the system but I have only ever seen no thermostsat cause overcooling.
Don't forget to use the correct coolant for topping up too.
Cheers
Stu
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Follow Up By: Member - Chris (QLD) - Saturday, Mar 02, 2013 at 11:41

Saturday, Mar 02, 2013 at 11:41
Hi Stu,
"Some people say that not having a thermostat fitted will cause overheating due to the circulation of the coolant being to quick through the system but I have only ever seen no thermostsat cause overcooling"

This is actually true, but the overheating only happens towards the rear of the cylinder head and not the overall cooling system. I have seen it a number of times with heads cracking at the rear due to no thermostat being fitted.
If you ever need to leave a thermostat out it is best to cut the valve part out the centre and put the rest in as this will slow the flow enough to cool the rear of the head properly, but as you say never leave a thermostat out.
Chris
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Follow Up By: Bushranger1 - Saturday, Mar 02, 2013 at 13:46

Saturday, Mar 02, 2013 at 13:46
Thanks for the explanation Chris.

Been working on my own vehicles all my life & no-one has ever explained the overheating effect of leaving out the thermostat like that. I always thought the overheating theory wasn't possible but that makes sense.
Cheers
Stu
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Follow Up By: Ross M - Sunday, Mar 03, 2013 at 12:55

Sunday, Mar 03, 2013 at 12:55
What people say and believe and what is actually true can be many entirely different things.
Can't see how it can be causing overheating with no thermostat, all thermostats are trying to be "no thermostat fitted" when the real overheating situation is occurring and maximum cooling is required.
Therefore,
I cannot see how the cutting out of the thermostat valve can alter the designed in cooling flows within the cylinder head, as these flows and circulation happen long before the water gets to the thermostat.

Also the same when the thermostat is on the intake side of the engine and not on the exit (hot) side of the engine.

People seem to forget it is the radiator which gets rid of the heat, not the thermostat.

Some of the previous comments don't make sense to me.

They seem to say, if you turn down the water valve on a nursing home wall panel heater it will get rid of more heat from the panel?????? Are we sure in this?
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Follow Up By: Bushranger1 - Sunday, Mar 03, 2013 at 13:15

Sunday, Mar 03, 2013 at 13:15
Pretty simple really. The thermostat is an automatic valve.

When the valve is fully open it allows maximum amount of water to flow through the radiator thus getting rid of more heat load from the coolant.
When it's closed or partially closed it restricts the coolant flow so that less coolant goes through the radiator thus allowing the engine to maintain it's optimum operating temperature no matter what the ambient air temp is.
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Reply By: Allan B (Member, SunCoast) - Saturday, Mar 02, 2013 at 11:18

Saturday, Mar 02, 2013 at 11:18
As said, almost certainly a bad connection and likely to be at the temperature sender on the engine. To test proceed as follows:
1) Warm-up the engine to get the temperature gauge needle 'floating', i.e. not sitting at the bottom of the scale. Stop the engine but then turn the ignition back on.
2) While someones watches the gauge wriggle the wiring connector on the sender to check for a poor connection. If found, clean the contacts and ensure that the connector it tight.
3) Wriggle the wire where it is attached to the connector at the sender. If this produces an effect on the gauge, repair the wire attachment to the connector.
4) Not likely, but it could be a faulty sender with an intermittent internal fault.
5) If no results to above, take it to an auto electrician.


Cheers
Allan

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Follow Up By: Member - Broodie H3 - Saturday, Mar 02, 2013 at 13:15

Saturday, Mar 02, 2013 at 13:15
I agree with all the above, I had the same problem with my HiLux and did all the above, took it to the auto sparkie to have it fixed he did the wire repairs and it was still happening, so we did a complete radiator flush and put in fresh coolant supplied from Toyota at great expense to me and that seemed to be the end of the problem sold the vehicle two years later and had no more heating hassles. that was my experience with that problem.
Broodie H3
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Follow Up By: Member - Broodie H3 - Saturday, Mar 02, 2013 at 13:21

Saturday, Mar 02, 2013 at 13:21
Just as an after thought, you may have air in the system too this could also lead to this problem that happened to me with my HINO I didn't heat the engine correctly to get the thermostat to open and allow the flow to go through the whole system, in the truck. It may be another option to look at. just a thought.
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Follow Up By: JohnnyC - Saturday, Mar 02, 2013 at 13:51

Saturday, Mar 02, 2013 at 13:51
If you pull the plug off the sender the gauge should go full scale, if you touch the sender wire to ground the gauge will go to min.
As you say your gauge is jumping towards the low side it sounds like the sender or its wire are shorting to ground somewhere
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Reply By: Member - Phil G (SA) - Sunday, Mar 03, 2013 at 08:52

Sunday, Mar 03, 2013 at 08:52
I had a fluctuating temp gauge on a similar vintage 60series.
Problem was the voltage regulator that sent power to the temp gauge. It was a simple bimetallic strip with contacts that would stick. It supplied power to both the voltmeter and the fuel tank gauge and the giveaway was that the fuel gauge fluctuated a bit when the temp gauge flew up or down. The regulator was contained within the fuel gauge so to fix the problem I replaced the fuel gauge. You'll need an factory workshop manual for your vehicle to see if its similar.

Cheers
Phil
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