Motor not reaching operating temperature

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2 months 2 weeks ago #201796 by mojo353
Hi There,
Newbie here...... My wifes truck ..96 Explorer 4L wont reach operating temperature. She has noticed it a lot heavier on fuel, I changed the thermostat but no change. Its not losing coolant anywhere and oil is good too.... not cloudy etc. The temp gauge on the dash reads way below half way, when we got the truck a few years ago the heat was amazing so the problem hasnt always been there. Ive noticed the top rad hose very hot after running for a while but the bottom one is way way cooler .... in fact its only warm. This would suggest a faulty thermostat to me or.... is it possible the sender unit is faulty ? Im assuming the signal from the sender unit not only goes to the dash gauge but also goes to the ECU ???.... and so the ECU reads low temperature and thus gives more fuel etc as if its a cold start ???.... I dunno Im guessing here..... The heater in the cabin doesnt blow anywhere as hot as it used to , the fan is fine - all speeds work fine..... just low to no heat.

Second issue is with my sons car..... 2006 Audi A4....... His wont blow heat unless the rpm is above 1500..... works good above that but instantly blows cold at idle. Coolant levels are good and no leaks ??

Any input or what direction to go with these issues would be appreciated, we are in Canada and its frikkin cold !!
Thanks in advance .

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2 months 2 weeks ago #201797 by relative4
Replied by relative4 on topic Motor not reaching operating temperature
Re the truck, did you replace the thermostat with OEM or aftermarket?

Re the Audi, the B7 heater cores clog easily, especially if someone put green coolant in it. It's fairly cheap and fairly easy to replace. I hook up a shop vac to the heater hose to suck all the coolant out of the core and don't get a drop on the carpet. Some people say to remove the accelerator pedal mechanism, I have found that entirely unnecessary. A coolant flush afterward will help prevent a relapse.

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2 months 2 weeks ago #201800 by mojo353
Replied by mojo353 on topic Motor not reaching operating temperature
Re The Truck:
Its an after market thermostat - Im going to pull it tomorrow and check it out, the odd thing is the one I took out was fine, I chose to replace it as a preventive measure but it didnt fix anything. Am I correct in assuming the temp sensor may be playing a part in this ? if so any idea what resistance I should be seeing across it at varying temperatures ? Im also thinking of running it without the thermostat for a bit with a cleaner in the system to flush it out, then drain, replace thermostat and re fill with fresh coolant but Im doubtful it will fix the issue.

Re The Audi:
I will try that with the heater core and flush the whole system afterwards. Hopefully it sorts it out, I will keep you posted.
Thanks for the input.

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2 months 2 weeks ago #201801 by relative4
Replied by relative4 on topic Motor not reaching operating temperature
You can test your thermostat in a pot on the oven. Either way I'd recommend OEM, aftermarket thermostats have a bad reputation. Also, you can consider using a differently rated thermostat, but it can be a pain to switch them twice a year.
If you have a good thermostat and are still overcooling, partially blocking the radiator is the next step. It can be as simple as cardboard. In very cold areas, some people block the entire radiator.
If you add your location to your profile, that will help give an idea of what you're up against.

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2 months 2 weeks ago #201802 by mojo353
Replied by mojo353 on topic Motor not reaching operating temperature
ok Thank you, I will try that and keep you posted.

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2 months 2 weeks ago #201805 by relative4
Replied by relative4 on topic Motor not reaching operating temperature
Oh hey, if you end up blocking the radiator, set yourself a reminder to remove it in the spring!

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2 months 2 weeks ago - 2 months 2 weeks ago #201806 by relative4
Replied by relative4 on topic Motor not reaching operating temperature
Oh, and I missed the part about the ECT sensor and the fuel consumption. That's a very good point. You can also test that on the stove, if you can find the resistance specs. Those sensors are pretty cheap, might be a worthwhile case of firing the parts cannon.
It would be good to investigate that possibility before blocking the radiator, so you don't end up overheating your engine while the ECT sensor is saying everything is hunky-dory. Especially given that the upper hose is so hot.
Some vehicles use separate senders for the ECU and the dash gauge. See if that's the case for yours.
Last edit: 2 months 2 weeks ago by relative4.

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2 months 2 weeks ago #201809 by mojo353
Replied by mojo353 on topic Motor not reaching operating temperature
Yeah mine has two sensors, I checked the gauge sensor and that was fine - also the gauge went straight to hot when the one wire to it was grounded. I had picked up a sender sensor when I picked up the thermostat - checked the new sender unit against the old and had a difference of 5 ohms ( new one reads 5 ohms higher resistance through the temperature range tested - roughly 0' C through to about 45 'C, so a constant 5 ohms throughout. Im pretty sure the new one is the correct one for my model truck) just about to do a coolant flush now without a stat fitted, I will compare both new and old stats to see what temperature they open at.
Will post results in a few hours.
Thanks so much for the help.

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2 months 2 weeks ago #201814 by mojo353
Replied by mojo353 on topic Motor not reaching operating temperature
So...... All sorted and back to normal. When I tested the stats the new one opened 10 to 12' higher than the old one. Turns out the old one was one of those fail safe ones ( Fails open rather than closed) it was also set for a lower temperature which would explain the heater not getting as hot - more noticeable here in Canada during the winter.
It worked fine - opening and closing just at around 80'. I put the new one in after flushing the system and filling with new coolant and ran the truck for a good 20 mins fast idle burping what air I could out of the system. Will check again in the morning to see how much it has drawn in from the reservoir as the top rad hose was still soft to the touch after the thermostat had opened and closed a few times.
The cabin air is much warmer and the temperature gauge rises to just below half way before the thermostat opens.
Having said all that I am delighted to have gotten this sorted, I do feel however that the cabin air was hotter going back maybe 4 years when we first got the truck. Im hoping by drawing more coolant in from the reservoir overnight that the remaining air will be expelled and the top hose feel harder at operating temperature. Failing that the heater core may require further cleaning/flushing.
Thanks again for the time and input, I really appreciate it. Always good to have someone else's perspective on these things.

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2 months 2 weeks ago #201815 by relative4
Replied by relative4 on topic Motor not reaching operating temperature
Glad to hear the simple fix was the thing. Thanks for posting results.

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