2002 Mazda Tribute LX 3.0 V6 199K miles

I replaced the leaking water pump, failed thermostat/gasket, and leaking degas reservoir. The radiator was replaced 6 months ago. The radiator doesn't have a radiator cap, rather a degas reservoir and the cap for that is what holds the pressure in the cooling system. I think this is called a "sealed" cooling system, and I'm not sure if it's also considered to be a "reverse" cooling system. I'm using P-HOAT coolant and distilled water. I'm getting plenty of steady heat inside the cabin.

I have no leaks, but the temperature gauge goes from just a hair above and below 1/2 up to 2/3 and even 3/4, then goes down to 1/2 and repeats the cycle. It seems to go down with the RPMs are up and the temp goes up at low to moderate RPMs. After the car gets up to operating temperature, the fans kick on at high speed and never turn off until the car is off, which doesn't seem normal.

I saw a video of a respected Ford mechanic who says to leave the cap on the degas bottle, start and idle the car for a minute, then increase RPMs to 3500 for 30 seconds, then idle for 30 seconds and turn off the car for one minute, then repeat that process several times until all the air is "burped" or bled out of the system. This hasn't worked for me and it seems odd that he says to leave the cap on tight while doing this. I spoke to a general mechanic (not a Ford specialist) who says to take the cap off the degas bottle when doing this. I would think the Ford specific mechanic would be correct, but I know with a regular cooling system with a normal radiator cap, we do have the cap off to bleed the air out of the system, which I have done many times on Camrys and Corollas without issues.

What's going on here? Should I ignore the Ford specialist and just do the process with the degas bottle's cap OFF?

 

I'd start by using a laser thermometer to find whether its the sender playing up or an actual physical temperature problem. If its physical then I'd suspect the thermostat, if not then the temp sender. Having the fans run full and constant sounds like a sender too - check the wiring.

I've never found the V6 that hard to bleed, if you still think it is air then try jacking the de-gas bottle side high while running. Try squeezing the upper radiator hose while running, make sure the heater is on full.

TBH try both mechanic's methods, its not like the "wrong" one will introduce air into the system...

 

simonsi, thanks for your reply. Tonight I just had it at idle with the cap to the degas bottle OFF and never increased the RPMs. The temp gauge never went past the middle. I had a scanner connected and the operating temp was pretty steady at 212 degrees F and it showed the fans coming on a normal speed when it hit 213 degrees F. Fans stayed on only for a minute and turned off when the temp dropped to about 203 F or so. They went on again later when it went from 212F to 213 F. I did use a laser thermometer after the engine was fully warmed up, but wasn't sure where to point it. I tried the laser at the upper radiator hose and it showed about 203 - 208 degrees F while the scanner showed 212 F. Is that a significant difference? I also tried pointing the laser at the thermostat housing and in front and behind it and it was always lower in temp than what the scanner was showing me. I didn't think to point the laser right at the temp sensor. I didn't have time tonight to drive the car or just to rev up the RPMs. I think driving it is when I get the erratic change in temp gauge reading going up to 3/4. I'll try driving it tomorrow night and see how it reacts to changing RPMs and will report back here. Thanks again for responding.

 

I wouldn't think those temp differences are significant, they all seem slightly below the coolant temp which is reasonable and to be expected. Good sign that the fans seem to respond as expected at reasonable temps too.

Could be the last cool down removed the last air pocket, is the level in the de-gas bottle stable now, check it when driven too, air out means water must go in ;-)

 

The level in the degas bottle was right at the cold full mark. I started it up and idled it for about 20 minutes and the temp displayed on my scanner was usually around 203F - 212F. At 213F the fans would kick on at moderate speed just for a minute or so. Also tested for carbon exhaust in the coolant and there was none, so it's not a head gasket problem. I then took the car out for a drive tonight. Once driving, the temp goes up. I had my scanner hooked up and it was mostly in the low 230 degrees F. Then the gauge goes from 1/2 up to about 3/4 and the scanner showed 239 degrees F. Can going up 9 degrees bring it from 1/2 to 3/4? Seems like an awfully big jump just for 9 degrees, or is that to be expected? Fans on at full speed constantly. Also, although the brakes look OK with nice, thick pads and no scoring on the rotors, they were making a high pitch whining noise that sounds like microphone/amplifier feedback. Not sure if faulty ABS makes that kind of noise? Also making a noise like the brake dust shields are touching the rotor, but I'm pretty sure they are not (will check them tomorrow night). I'm wondering if the brakes are slightly stuck on and that's why the car gets hot while driving, but doesn't while parked and idling. I ordered a new temp sensor and will get it on Friday evening. Will get the vacuum air bleed tool tomorrow night. No check engine codes at all, btw. Well.....let me know if you have any ideas, thanks.

 

Modern temp gauges aren't necessarily reading the temp, sometimes they are designed to indicate cold/norm/hot based on an output from the ECU that isn't necessarily a reflection of the precise temp - so the actual temp may fluctuate but as long as the temp stays in the design range then the gauge will stay at normal.

That said, mine is steady as a rock and you'd have to have red hot brakes through binding to raise the temp, raising the temp implies the cooling capacity of the system is being exceeded - Which maybe towing a heavy trailer uphill in very hot weather might do...not something I'd expect of a biding brake without a) red hot/faded brakes and b) worst fuel consumption in the world.

As your rad is nearly new we can assume not clogged, that leaves a faulty thermostat or pump. Circulation seems OK as you say the heater output is steady...so I'd suspect the thermostat first - but it could be the pump impeller is slipping on the shaft, I have seen cheap new pumps do that, especially if the impeller is plastic on a steel shaft....Your choice which you swap out first to prove though.

What made you think the original thermostat was faulty?

 

The new GMB water pump has a metal impeller. I replaced the thermostat because I tested the old one in a pot of boiling water and it never opened up. The replacement thermostat was the Murray brand. I don't know if Murray is thought to be a quality product or not. I installed it with the jiggle valve at the 12 o'clock position. I can try switching the thermostat out again with a Ford or Mazda thermostat tonight or tomorrow.

Interesting that you brought up towing uphill. I've also noticed that the transmission slightly slips on the highway only when I try to step on the gas to pass another car (seems like the car is struggling and the tranny is not fully engaged) or when it's slightly uphill (same struggling). On the surface streets the transmission behaves normally. I was going to focus on the transmission and brakes after I got the cooling problem resolved. Not sure if they are related to the overheating, but no, they weren't red hot brakes or anything like that. Just that noise that I described earlier that sounds like amplifier/speaker feedback.

I really appreciate your responses, so thank you. This is my daughter-in-law's car and I'm trying to help her out since she's broke.

 

Haha - I have two Tributes, 2001/2002, mine and my daughter-in-law's and it gets maintained on the same basis as yours :-)

If the original thermostat didn't show a problem in service then I would put that one back in, or a new Ford/Mazda as $$$ allows vs time spent.

The CD4E tranny is quite aggressive with the O/D lockup, when you go to overtake it has to unlock fairly easily which will give you a normal slightly elastic feel to the drive, what you feel maybe just that.

Brakes sound fine, not contributing to the coolant temp issue by the sound of it so we should focus on the thermostat and pump, metal pump sounds like it should be good. Sorry I don't have experience with GMB or Murray brands locally (NZ), so can't comment.

 

Hi, glad to know I'm not the only FIL fixing a Tribute/Escape.

The original thermostat was bad. I tested it in a pot of boiling water and it never opened. Murray was the only brand available at that time. I'll try and pick up a Ford or Mazda thermostat tonight on my way home from work. Will keep you posted and thank you for replying!

 

Fixed:

I finally got the time to replace the new cheap Murray (made by MotoRad) brand thermostat with a "Genuine Mazda" (Ford Motorcraft) thermostat. Problem solved.

So, for thermostats I already knew to go with OE, but it was late in the evening and I was in a different city working on my daughter-in-law's car and the local parts store was my only option. My advice is to avoid Murray or MotoRad thermostats.

Oh, I wound up using a vacuum purge/refill tool. It is a really convenient tool and you don't have to worry about air pockets this way. I used it with the Murray thermostat and it still overheated, so I think I did have the air purged the first time but it was the cheap Murray thermostat that was causing the problem. Used the tool again with the Ford thermostat.

Thanks simonsi for responding to me. I appreciate the input.

Here's the vacuum tool I used:

 

Glad you got it fixed - cooling faults are always worrying.