claus

Newbie here with an overheating problem.

I have search, and found, prior post relating to my issue, but have not found any that exactly matches my specific issue, so I am kindly asking for help diagnose my baby's problem.

I have owned my 4runner (SR5 with about 280K miles) for about a year now, and it was purchased in order to cope with our move from sunny Florida to the hills of West Virginia with the changing seasons. In the beginning almost everything was well driving in Florida. Temp gauge doesn't work so I added a ScanGauge2 to the diagnostic port, and in FL temp stayed around 186-188, occasionally jumping to 190. Pretty standard stuff and in line with what it was supposed to be. I had a couple of trips from FL to WV with no temp issues at all.
The problem started after I pulled an enclosed trailer and the truck filled inside the 850 miles, all with OD off. I could do about 60 mph and keep the temp around 180-190, again pretty much on par with what I expected, but on the return trip with an empty trailer it was the same issue. At no time could I sneak above 60 mph without the temp climbing.

Before my 2nd trip north with the trailer I replaced the radiator and added an oil cooler in series with the one in the radiator (over a period of 2 weeks I kept an eye on the temp and added fluid as the system burped out the air), but the problem persisted on my 2nd trip, or maybe a bit worse than on the first trip.

I knew that the engine was pinging, and the time of last timing belt change was suspect (a prior owner threw in a different engine at some point, not noting the mileage of it), so I had a shop replace the timing belt, the water pump and thermostat. After getting my truck back I noticed, that the temp would climb to 192-194 with normal driving on some moderate hilly roads, so I took it back to the shop and they replaced the thermostat with one that opens at 180 degrees. That didn't change anything, and the temp still climbed during normal driving.
I had to go out of town, about a 30 mile trip with some serious hills, both steep and long, and minding my own business and daydreaming I forgot to keep an eye on the engine temp. When I finally noticed it, it was at 196 and climbing, so I disengaged the OD and the temp stabilized going uphill.
Next steep hill I kept the OD off and tried to keep the speed at the 65 mph limit, but the temp climbed steadily from 186 to 194 again. Next hill I stayed below 60 mph and the temp remained stable at 190.
The problem occurs consistently when the engine is under just a slight load.

I have deducted, that keeping the rpm's above 2500 helps the problem climbing hills, as long as I stay below 60 mph and the hills aren't too long. Coasting down the hills, the temp drops at a good click, as long as I can keep the rpm's at 2000 or above. At prolonged idling the temp stays at 185, and raising the rpm's to 1500 makes the temp drop to 181.
The problem persists even with outside temps below freezing!

I read in one of the prior posts, that filling the coolant system with some sort of engine flush and driving with it for a week of so could help, but the name of the product eludes me.

Another problem could be the fan clutch, but I doubt that since the temp is fine at idle. I have a new clutch that I will install as a precaution.

My fear is, that I somehow got a bad water pump, and that I have to replace it, not something I am looking forward to.

If anyone here has another idea, that doesn't involve a major teardown to do, I am all ears...


Thank you all for your help!

Marc

194 is not a problem. That's not overheating.

Kolton5543

Your running at a pretty good temperature actually. Pulling a trailer up hill at 195 is well within reason. I would get slightly concerned at 210 and decide to finally back off at 220. If your worried it sounds like you may have a fan clutch working its way out out but I doubt it. I'd keep rolling with it and of it doesn't get over 200 up a hill there's nothing to.be worried about.

claus

Maybe I'm focusing on something minor here, but mentally I keep referring back to when I drove it in Florida.
Another time I drove from WV to FL with 3 people and a utility trailer loaded with a tow dolly, and I kept my eyes glued to the temp gauge. 60 mph was all I could do before the temp would start to climb.
If I was going up a slight incline and the tranny shifted down about 300 rpm's (that mysterious gear between OD and 3rd), the temp would shoot up at an alarming rate. The only remedy was to switch off the OD.
We spent a night at a hotel in SC along I-95, and having all the hills behind us I could that morning sneak the speed up to 70 mph while keeping the temp under 190, but as the day progressed and the ambient temps rose, so did the engine temp and we ended up going no more than 60 from GA to our destination in FL.

I may not have a problem at all, but I doubt that is the case. When parking my truck after the temp has gone to 192 ( it is mostly uphill going to our house) it even smells hot from the outside, and the wife even commented on that yesterday.

In my mind the problem has to do with coolant flow. It could be restriction in the system from the radiator and back into the engine. When I did the umphteen try at burping it a few days ago, I noticed the the top radiator hose was still soft and and easy to squeeze when the thermostat was open.

I'll stop at AutoZone today and pick up some coolant system flush, and if that has no effect then I have to replace the water pump.

Marc

You say temperature would "shoot up", shoot up to what?

That mysterious gear is the torque converter locking and unlocking.

Are you sure you're not monitoring the transmission temperature?

In any case you should be.

I'd be way more concerned about it than a non existent engine temp problem.

It may very well "smell" hot. They are hot normally.

Kolton5543

The mysterious gear between 3rd and 4th is the torque converter clutch disengaging. In the converter there is a clutch that locks the engine to the transmission without any slippage. It's there for fuel efficiency and reducing transmission temps. When the clutch is disengaged the torque converter will allow slippage between the engine and trans. When under a high load this build a great amount of heat. You see it in your engine temp gauge because the transmission cools it's oil using engine coolant.

if you have soft hoses when hot then your cooling system isn't under pressure. That means you either have a coolant leak somewhere or the radiator cap isn't holding pressure. How's the coolant level in the reservoir? If it's way full when hot then I bet on a bad cap. They're cheap enough that I would just replace it anyways. They are kind of a wear component that often gets over looked during regular maintenance.

claus

I figured that it was the torque converter doing its thing in regards to the mysterious gear.
The tranny is ok and not overheating, especially since I added the tranny cooler, and I have not had a problem with it. Not sure this is related to the transmission, but sometimes going up the long hills it will kick off the cruise control if I have it engaged. Not a problem I have during normal driving with an empty truck. It happened on my trips to WV from FL when I the truck was filled with moving items and pulling the small utility trailer.

I am not losing coolant from anywhere, and It isn't milky in color. The expansion tank is half full, give or take an inch depending on the engine being cold or at normal operating temp.

Thanks for the advice and I'll update this thread after I have run the system flush for a few days.

claus

Marc,

When I said shoot up I meant that it would rise rapidly at 1.8 degrees every 5-7 seconds, whereas in OD it would go up the 1.8 degrees every 15-30 seconds. I could stall or limit the increase by switching off the OD.
it would go from 186 to near or above 200 in a matter of a minute.
The 1.8 degrees is the increments on the scangauge2

Kolton5543

Well the temp would definitely rise quicker in 4th than it would in 3rd as it puts a great deal more load on the engine and transmission. Still 200 isn't anything to worry about. Have you let it keep rising past that to see if it flattens out or keeps rising. Your safe for another 20 degrees or so, so give it a shot. As for smelling hot it'd kind of expected. A lot of hot smell comes from things burning on exhaust and such. The temperature of exhaust manifolds aren't directly related to engine temp and will get way hotter under extended load that they will with normal driving. Put a cap on it and see what happens. The problem with us helping you is it doesn't sound like there is much of a issue.

claus

In a former life I cooked an engine and that may be the reason I'm a bit nervous about it.
I also keep going back to when I drove it in Florida, and the temp never got above190.

Anyhyr, I put Prestone flush in the beast and will drive it for a few days. I'll let y'all know how it turns out.

Thommo Thompson

Id say the problem here is probably the units used. fahrenheit. those figure differences looked significant to me too (im an aussie) but when i convert them to a useful measurement; celcius, which is based on a scale upwards from freezing, then u are moving only about 3 percent over a scale ranging from freezing to boiling (water)

claus

Thommo,

Yes, when converting to Celsius the temp rise looks smaller and less of a problem, but it's the optimal temp operating range that should be the focus point.

Perhaps I have been misinformed when I read a few places, that the optimal temp range is between 186 and 192, which puts the median temp at 189F.
coupled to that the distinct "hot" smell when I park the truck after it has reached 192-194F.

Other trucks performs better at higher temps much closer to waters boiling point. Chevy trucks should be closer to 210F for optimum performance, which leaves preciously little room for increased temps under load.

There are also differences between two identical models, especially when we are comparing almost 20 year old trucks, and the owners experience with each will tell them when something isn't quite right.

Kolton5543

It doesn't matter if its Celsius or Fahrenheit. either way the temperature is the same just on a different scale. your right on the operating temp range. optimally these trucks should be around 190ish. But the cooling system may be unable to support that temperature under extended heavy load and will likely rise a bit. As for 210 being near boiling point you'd be right if it isn't under pressure. the cooling system system should be under pressure raising the boiling point to aourn 250ish

claus

Update after running Prestone coolant flush:

With the coolant flush in the system I took the truck to town today and wouldn't you know it, the temp stayed pretty much in the range I had while driving in Florida.
actually perhaps a bit cooler due to the 180F thermostat. Most of the driving it kept in the 183-185 range, and only during the longest uphill sections did it reach 190 and only briefly. Most uphill driving it was at 186 and 188F.

The coolant I drained wasn't as bright red as I expected, more orange slightly towards yellow.
wondering if the shop that replaced the timing belt used some generic coolant and not the specific type required by Toyota, and also wondering if that had an effect on cooling????

Anyhyr, got some coolant that states it's for Toyota model years 1996 to 2004 and that is going in on Friday after I drain the Prestone stuff.

Thommo Thompson

is the prestone flush in there with plain water? if so, that might be why there is better cooling.
adding glycol does significantly affect the coolants ability to give up its heat to the radiator tubes, and it also has an effect (but not as big as the radiator heat exchange) on its ability to conduct the heat from the block and head. however i woyldnt recommend running water alone as there will be time when u have to push the engine above the limit of waters boiling point, even when preasurized in the system.
if ur finding a 50/50 mix giving problems, try changing to 70/30 (70% distilled water). this might seem like a tiny difference, but the changes u are seeing in temp are also very minimal so it may be all that is need to keep it under control.

claus

According to the directions on the Prestone flush I just added water after dumping it in the radiator.
Today, after I take it for a drive, I'll dump the coolant flush, run some plain water in it for 10 minutes after it reaches operating temp, and drain it and add a 50/50 mix of Toyota specific radiator fluid and water.

I'll post my findings here when I have had a few days of driving with the fresh coolant.

Marc

Don't forget to put both front and rear heater controls to hot to flush the heater cores as well.

Thommo Thompson

hmm, that will be intereating to see how much a difference coolant makes. not many people have such statistcal data to show the difference in a real world situation, but its supposed to theoretically cool better with no glycol. so maybe thats what ur experiencing.
please dont leave us hanging, no matter what ur findings are, please let us know.

Thommo Thompson

also, which exact fluah product did u use. acidic, or std?
the acidic formula stuff is strong and i could be convinced that it dislodged a fair bit of blockage from the radiator. but the std stuff is just good for a preventative flush and wouldnt change much internally.

claus

Took the truck out yesterday before I drained the Prestone stuff, and the temp went slightly higher than on the last trip. Not too worried about it, just slightly concerned.
When I got home the expansion tank was empty, but I hadn't burped the system after I put the flush in it.

Drained the coolant and refilled with plain water and ran it for about 15 minutes after it reached operating temp. Drained it and repeated a second time before filling it with real coolant.

To be honest the Prestone flush I drained wasn't that bad looking. No real amount of particles just a few black things which I believe was probably from the rubber hoses.

I'm still concerned about the top radiator hose not being hard when the engine is running at raised rpm's. I shouldn't be able to pinch it completely together, right?

I'll keep you posted.