Truck Not Heating To Proper Running Temp

Hi all. I was hoping some automotively savvy person might give me some advice.

I bought a 2001 Mazda B2500 SE in around July of this year to use as a economic work vehicle. The truck has 73k miles and is mostly in very good condition.

The other day my check engine light came on. Simultaneously my heater stopped blowing hot and only blows warm. My temp gauge is buried and only moves when I really run the truck. For example, yesterday I had some work out in the middle of nowhere, had to drive up a mountain pass to get there. By the time I got to the top my temp gauge had creeped up to about 1/16 the length of the gauge. (It's usually buried far below the starting point.)

I had the codes read and the code that popped up was saying the engine wasn't getting up to proper running temp. My first thought was that the thermostat might be stuck open - so after waiting 5 days for the right O-Ring to arrive I replaced it today. The temp gauge is still buried and the heater is only blowing warm. I've already verified that all vac lines are wired properly, and everything else works fine. I'm also getting poorer gas mileage than I originally did, but I assume that's because the engine is burning rich because it's not getting up to proper temps.

Both the up and downstream o2 sensors have been replaced within the past 5 days.

Does anyone here have an idea what might be causing this? I live in Northern Utah and it gets pretty damn cold here - especially when you leave the house at 06:00 or earlier. If I can give you some additional information please let me know.


Thanks in advance.

reply to post by TinkerHaus


I should also mention that all air filters have been replaced. When replacing the thermostat I also completely backflushed the radiator with distilled water and replaced the fluid.

This happened to me because the electronic temperature sensor on the radiator that told the fan when to be on was faulty, so the fan was on all the time. Even at -20C.

reply to post by TinkerHaus


Sounds like the thermostat is stuck open or was taken out. If the heater wasn't working but the gauge was the right temp, I would say it was low on water. It would pay to check the water anyway, maybe the gauge isn't working right and the water is low causing the heater not to throw out heat. Use 50 50 antifreeze if adding water to the radiator or the jug.

dainoyfb
This happened to me because the electronic temperature sensor on the radiator that told the fan when to be on was faulty, so the fan was on all the time. Even at -20C.

Thanks. You know, I was idling it for about 30 minutes today and noticed that the fan was on at all times as well. This very well may be the answer I was looking for. Truly appreciate your response.

rickymouse
reply to post by TinkerHaus

 

Sounds like the thermostat is stuck open or was taken out. If the heater wasn't working but the gauge was the right temp, I would say it was low on water. It would pay to check the water anyway, maybe the gauge isn't working right and the water is low causing the heater not to throw out heat. Use 50 50 antifreeze if adding water to the radiator or the jug.

Not sure if you read the entire OP - but the thermostat was replaced today. Radiator was back flushed and refilled with 7 quarts of 50/50 mix as the manual specifies. Radiator is full of the proper coolant/water mix. And yes, I care about my vehicles and use distilled water for both the flush and to refill.

The thermostat on this particular vehicle is a real PITA. There is a plastic housing that has two 8mm bolts that are just BURIED under a ton of crap. I had to take half the damn car apart to replace it.. But yeah, everything you've mentioned has been gone over.

I think the poster just before you might be on to something.

I just read your second post. Is it an electronic thermostat that uses a heat sensor to open by any chance? I don't know much about Mazdas. If the sensor isn't working in that case it opens the circulation. The fan can be running all the time also and this can cause the engine temperature to go astray.

reply to post by TinkerHaus


Hope it solves your problem. Keep in mind that it could be anything between the sensor and the fan too. Like something in the computer that controls the fan or the wiring. The sensor is the most likely failure point though due to its fragile nature and the extreme environment it is in.

Let us know how it pans out.

You can test the sensor before you replace it if you have a multimeter. You will have to Google it and find out if it is a switch or resistive. Make sure you do this with the engine off and the sensor disconnected from the wiring harness.

Wouldn't hurt to just give the connector on it a wiggle too.

reply to post by TinkerHaus

You may have a bit of a air lock in the heater core but that shouldn't make the engine run cold .I was thinking there may be different thermostats too like a winter one and a summer one ..It's been years for me working on them and I really couldn't say for sure .best of luck to you though .

reply to post by dainoyfb


So the fan is running 100% of the time. It's about 10f outside and the fan runs as soon as I start the truck. A little googlin' has told me that my truck doesn't have an electronic temperature sensor to run the fan - instead it has a fan clutch which has a coil on the fan that senses the temperature coming off the radiator and kicks on or speeds up as the engine gets hotter.

I've ordered the part and it should be in tomorrow.. Really hope this is it. Thanks for your suggestion, definitely pointed me in the right direction (I hope!).

reply to post by TinkerHaus


I would have suggested that the thermostat is stuck open but you got that one. I'd say keep goggling it on specific Mazda automotive forums. Good luck, I know you'll find the solution.

reply to post by TinkerHaus


Fan on all the time, or bad thermostat.
You will know if the fan is on full time as you will see it and most probably hear it.
If that is not the case, pull the old thermostat and put it in a pan with hot water and a cooking thermometer, at 190 or whatever the manufacture recommends, the thermo should open and not before.
If both of these are not the case, maybe a hotter thermo, 10 degrees up.
Hope you figure it out as cooling issues can suck!!!
Been there, done that, bought the grease stained t-shirt!
AAAAAARGH I hate automotive work nowadays.
(Edit)
AAAAH I see it is a mechanical fan and not electric, mmmhm fan clutch.

So I tested to see if it's the fan continually blowing by removing the plastic fan from the clutch and idling the vehicle. After 10-15 minutes the temp gauge was SLOWLY creeping up, but was still below the gauge parameters.

I took it for a 10 minute drive, and while the heater is blowing noticeably hotter the temperature gauge is still not getting to the point it should - in fact it's not even getting to the bottom line of the gauge, although it is getting CLOSER to the bottom line than it typically does.

I wonder if I have a bad gauge ON TOP of a fan clutch problem. I am trying to figure out if the computer that sends error codes gets it's information directly from some temperature sensor, or if it is after the instrument panel - or perhaps there is some temperature sensor that feeds both the gauge on the instrument panel AND the computer, and that's why it's throwing the "engine not getting up to running temp" code. So maybe there is nothing wrong with the gauge itself, only whatever temp sensor the gauge gets it's information from.

In any case, completely removing the fan did seem to have a positive effect on both my heater and how smoothly the truck was running.

I'm stumped. =\

Also, I love people giving me advice to do things I already have and have already stated in the OP. Before you can help someone resolve a problem you have to first UNDERSTAND the problem, which requires knowing what steps have already been taken to troubleshoot/resolve the problem. Y'all should go work tech support somewhere.

reply to post by TinkerHaus


Not sure about the Mazda, but I know my truck has two temperature sensors, One is for my dash gauge, the other is for the computer... in some cases the sensor for the computer will cause this issue.

If it's OBD II > Common Problems That Trigger the P0128 Code

Defective Engine Thermostat
Defective Engine Coolant Temperature Sensor
Defective Intake Air Temperature Sensor
Defective Cooling System
Low Engine Coolant
Dirty Engine Coolant, causing incorrect Coolant Temperature Sensor readings
Defective, always running Engine Cooling fan(s)

reply to post by TinkerHaus


If you find the clutch fan to be at fault, consider ditching it in favour of thermo fans ( thermatic electric ). You will gain a little HP and save fuel - they are also much quieter.

Good luck.

www.daviescraig.com.au...

It is a thermal fan clutch.

Getting tired of people just throwing what they googled at me. =\


Also, replaced both temp sensors, ran truck with the fan clutch installed but fan removed, tested temp gauge by grounding the lead and it performed as it should. Backflushed and refilled radiator with 50/50 mix. Burped the cooling system to ensure there are no air pockets.

Anyone have an idea what else might cause this? I'm done working on this for tonight - I have a feeling it's a problem with the trucks computer. Everything else is checking out.

reply to post by TinkerHaus


No clutch in the fans that I have personally switched to only electric motors powering them.

ie. no fanbelt needed for cooling fan.

Does yours run off a belt?
You are confusing me with the term "clutch".

If yours does run a belt to your fan - you have misunderstood my well intended advice and could do well to re-read.

Have you tried to unplug the battery & let the computer reset just for the hell of it?

I hope you tested the thermostat you put in before you installed it...If you already said you did then I missed that