Is this 7MGE overheating or some other issue?

In my experience, overheating engines would have some slight loss of power and pinging sounds prior to reching the red zone. Do you experience any of them?

In my experience, I have never really noticed a loss of power. The only times I have noticed relatively less power was when I had a load of people in my car or in a Toyota SR5 truck, I had a load of cylinder heads in the back (17 if I recall). In both cases, I would estimate that the weight of the load was about 2500 N (mass of about 250 kg - the people included two kids). I also used to carry engines, speedy dry (once when the truck had only 5th gear - the fork got bent), and junk parts to the recycling center and other stuff - but what was different these two was that I didn't expect lower acceleration to the extent that it was.

Even when I load the car with books or other items, I don't really notice less power. I just push the accelerator a little harder.

So, my question for Ed is, how much less power would there have to be to really notice it? (In the above cases, the power was the same, just lower acceleration because of the mass of the vehicle and what it was carrying). I would think a slight loss of power would actually be a significant loss of power.

Jeff

Have you removed the bottom shroud?

Several things can cause an engine to run hot. Check the coolant mix, make sure the fan shroud and under-engine shrouds are in place, check to see that coolant is actually circulating, check ignition timing. When the engine is indicating hot, shut off the engine and see if the fan clutch is engaged. If you replaced the thermostat yourself, make sure it is properly installed (orientation of the spring and jiggle valve) and if you used an aftermarket thermostat, make sure it is also properly seated.

Check the coolant temperature sensor voltage and associated wiring.

The under-engine shroud was removed when it began to hang due to the screws tearing through. However, it ran for a long time that way with no issue. I wasn't aware it was crucial for cooling, I thought it was for aerodynamics or to protect the engine from debris.

The fan shroud is missing a piece that came flying off some time ago that appears to have covered maybe 25% or 30% of the shroud circumference on the bottom, so there's a gap on the bottom. But again, ran that way for some time with no issues. That temp needle used to stay locked to the center.

This may be hard to answer, but how "stiff" should the clutch be when engaged by heat? I'm a bit leery of the fan clutch since that's what appeared to have caused it to overheat necessitating the rebuild to begin with. Had no idea they were that crucial.

I just experimented with the engine cold - when I try to give the fan a forceful spin by hand, the amount of resistance sems to vary. It might "spin" only the distance of the space between two of the blades, though on some spins it feels a little looser, maybe moving the distance of 3 or 4 blades. Will have to try it hot.

Shouldn't the fan clutch get tighter as the engine gets hotter?

This particular fan clutch doesn't have many miles on it. A couple thousand, if that. I had replaced it when I was having overheat problems before and that seemed to cure the problem but apparently the horse was already out of the barn, the head gasket developed issues shortly thereafter.

Could you elaborate on this? As far as orientation, you mean whether it's in backwards or is there a certain clock orientation where it should be?

Hmm. Any tips on what the reading should be and how it should be checked? It's my understanding that the sensor is the brass piece that has a spade clip and screws in to the side of the thermostat housing, correct? I know that's what makes the temp gauge go limp when removed.

One other thing, when I put the new head gasket on, I did notice that the holes on the new Felpro gasket didn't quite match the water jacket ports precisely. There was a certain amount of area that they covered over. Is this likely to be significant? Are they supposed to fit the contour of the water jacket ports precisely? As near as I could tell, there was only one way the gasket would go on and actually fit properly so I'm as close as I can be to 100% sure it's on the right way.

Is the only definitive way to tell what the water temp really is to screw in a temp gauge that fits the sensor port and watch it as I drive around?

Thanks for all feedback.

The fan shroud and under-engine shroud are important but not critical.

The fan should spin freely when cold with very little resistance. It should be almost locked when the clutch is hot, so yes, it should get tighter as the engine gets hotter.

Generally, the spring should face the engine block. The jiggle valve is basically a hole in the thermostat flange with a piece of metal that looks like it got stuck in the hole. If the thermostat flange is not horizozntal when sitting in the thermostat housing, then the jiggle valve should be at

12 O'clock. Also, as Hachiroku found out, aftermarket thermostats do not always fit snugly in the thermostat housing and can become partly dislodged when the housing cover is installed, causing some wierd problems.

Sorry, I can never remember and have to look at a manual for voltage readings. Voltage should be low when cold and higher when hot.

I suspect that the head gasket may be the source of your problem. The holes shold fit the water jacket ports precisely. If they cover the holes, they will obviously will restrict flow, and the flow of coolant may have softened the gasket material to the point where it collapses when coolant is flowing under pressure.

That works, or you can remove the radiator cap when the engine is cold, stick a thermometer in the neck, start the engine, and see if the coolant temp matches the thermostat's opening temperature when the coolant starts to flow through the radiator, and if the coolant temp is around 180 ~ 200+ when the instrument gauge indicates normal operating temperature. You will probably lose a little coolant when you do this, so have some extra on hand.

Also, make sure you hve the proper coolant mix - too much or too little concentrate can cause overheating.

You're welcome and good luck!

This is true! However, in my case, it was on the Mazda, and was installed vertically instead of horizontally. Why did they do this????? Also, I had to replace a bypass hose last week. It they had moved the nipple on the heater tube three inches forward it would have made the difference between a half an hour to 5 minutes. Remember I said I wanted to punch an engineer in the nose every once in a while? ;)

In the case here, I did notice my Supra running a bit warmer without the bottom shroud in place. I had the same trouble HiC did, but I used some cable ties to hold the broken pices in place. It does make a difference. However, in my case, it was also the fan clutch that had gone bad. It looks like HiC covered all of that. Perhaps the thermostat is installed backwards.

On one of my Subarus, there is NO WAY to install the t-stat backwards, cause the spring is so damn huge it won't fit backwards!

This one has me stumped...it looks like HiC has covered all the bases, unless he's replaced a bad part with a defective part...

The OP should check the replacement fan clutch operation and also think about the part of the head gasket that is obstructing the cooling jacket holes. Unfortunately, this is not that easy to check :-(

He could have something like my problem, where the replacement thermostat has a considerably smaller orifice than the original equipment, but as this is the first time I've ever heard of such a thing let alone had it happen to me, it's a long shot.

Okay, some more observations. Last night I put a temp gauge in place of the temp sender and duct taped the dial where it was visible low on the windshield. The sender cable was snaked inside of the engine compartment being careful not to interfere with anything, be in danger of laying on the exhaust manifold, fall into the fan, etc. and carefully verified that the hood wasn't going to crimp it when shut.

Driving around from speeds from idle to to 60 or so, I found the gauge varying between 188ish to about around 200. Not sure what the temp rating of the thermostat in place is. The outside temp was probably in the low 50s or high 40's.

As suggested, I checked the tightness of the fan after the veh had been up to speed for some time. I finger spun the fan and found it to be much *looser* than it had been when the engine was cold. I installed yet another fresh from Autozone fan clutch since the first one is a liftetime warranty and figure I can always take the first one back and get my money back under the warranty. It behaves essentially the same way, much looser hot than when cold when hand-spun.

This seems backwards from how I understand them to work. Is hand- spinning the fan clutch with the engine off a valid way to test it? Does it require the centrifual force to operate or should it be noticeably tighter hot than cold when hand-spun? Actually, the one time I heard a noticeable whooshing change in the sound of the fan was a few moments after first firing up the car, when still cold, it behaved like it was tightening and moving more air. Is it possible that Autzone's fan clutches are just uniformly junk and I just haven't gotten a good one yet? Both of these fan clutches feel quite tight to me when holding them in my hand cold and turning the shaft by hand.

When I first got this car, the temp gauge stayed locked in the center, I was actually concerned whether it was working correctly.

Autozone showed 2 thermostats for this engine. A 180 deg and 192, showing 192 as the factory spec. I'm going to try a new 180 deg and see if that has any effect. Yes, the current therm is installed correctly AFAIK, the "snout" side toward the upper rad hose, the spring side toward the engine side of the therm housing.

As far as the head gasket, it's a Fel Pro that's supposed to be for this engine. Isn't Fel Pro supposed to be pretty reliable as far as fitting the way they're supposed to? I'll put another one on if nothing else seems to cure the issue, but not relishing going through that drill, not to mention expense.

This is about right. Thermostats are not really accurate, so around 200 degrees is just about right. If this is where it stays, I wouldn't worry a whole lot. If "around 200" is OVER 200, I'd try the lower thermostat and see what happens.

Mine spins tight when cold, but also tight when hot. Not quite as tight, but you can't spin it with a flick of the wrist, either. It moves 3-4 blades when spun hot.

Also, the AZ clutch can be HEARD when coming on at highway speeds. The damn thing sounds like a B-17 taking off! If the guage goes up, and the fan comes on (and you hear it) and the guage goes down, the clutch is working.

Actually, if you're not overhauling the engine, replacing the HG on this car isn't a lot. Shoot, you're 2/3 of the way there when you replace the spark plugs and the valve cover gaskets!! All there is left is to remove the intake runner and exhaust manifold, and then unbolt the head.

I had a very similar problem to what you're having, and thought I was on my way to a BHG, but replacing the fan clutch and then the shroud under the car resolved it.

But note: after replacing the fan clutch, the temp was NOT as rock steady as it had been before the OEM fan clutch went bad! I notice the guage moving up and down a bit, but it never gets over 1/2 way up the guage.

Hmm, so maybe worth the extra yen to buy a gen-yoo-whine Toyota fan clutch from the dealer? Or is there some other vendor that's just as good or better? I actually started a new thread on that topic.

I keep reading that they're supposed to be loose when cold, tight when hot...?

Those temps are about normal. If the gauge is reading high at that point, then there is a problem with the coolant temperature sender, instrument panel gauge, or associated wiring. My guess is the gauge or temperature sender.

Yes, it is possible that the aftermarket fan clutches are uniformly junk and you have not gotten a good one yet.

Don't bother with the thermostat. I don't think the thermostat is the cause of the problem.

Fel-Pro has a reputation for good gasket products. I suspect that the application information was incorrect, rather than the gasket being defective.

Before you go swapping any more parts, think about installing a separate coolant temperature system, or at least get the spec for the correct voltage from the coolant temperature sender, hook up some long wires into the passenger compartment, hook up a volt meter to the wires, and monitor temperature by voltage. I suspect that the car is not actually overheating.

You don't have to take my work for how the fan clutch works, check this web site:

google "engine fan clutch"

Ray (and likly that URL) is/are quite correct Also, don't think that just because you think you see fluid running in your radiator that it's not plugged. I know from experience. A radiator is cheap compared to a new head gasket or, worse, replacing the head.

Oh, I believe you, I just don't see the ones I have behaving that way. Either the one that's about a year old or the one I got the other night. I'm wondering about whether the Autozone models are decent. Torquflo is the brand name cast into the body of the clutch. I assume it's some in-house brand, made in China of course.

I've been going with the 50/50 stuff, should that be good?

As a follow-up, I found that the thermostat that was in there was 195 deg. I replaced it with a 180 degree and after running around for about 45 mins parked idle, stopped at lights, 80 on the highway and various points in between, the temp gauge appears to be back to pretty well locked in the center of the normal range as it once was. Once warmed up it varied maybe the space between two painted dots on the gauge.

Maybe there's nothing wrong with it running hotter but it makes me nervous when that needle edges up toward the red end. Or maybe the 195 deg thermo wasn't flowing adequately.

LOL! Yeah, ordinarily, but we're talking AutoZone/Chinese parts here, unless you sprung the Toyota OEM price for the Beck/Arnley, and then if you did you should have gone to Toyota in the first place!!! :)

Mine spins stiffly when cold, then loosens as it gets warmer and then locks when hot. Once the car gets up to operating temp, the fan spins quite freely, and when hot is quite stiff. But it is also stiff when the engine is cold, too.

The problem with using aftermarket parts is that their quality is a hit or miss and you have to experiment to find good ones. Some work fine, others do not. The automaker has done all the experimenting with OEM parts so you know how they will work.

50/50 is just right!

I don't recall the spec for the OEM thermostat, but the replacement should be the same. If the 180 degree thermostat works, then stick with it.