overheating? thermostat? cap?

[old blue jeans]

I have an 85 4wd that is getting hotter than normal, but not overheating; yet, I think. The sending unit is new, but not the thermostat, or radiator cap, and the heater core is new. Went to the parts store and picked up a thermostat and it's huge, it looks like there is no possible way it will fit. Is it worth my time to go back and get one that might fit? I'm not convinced its the thermostat. Could it be the cap, and its not getting the best circulation? Is this a better explanation for getting hot but not overheating? Is it more likely a clog in the radiator?

[irowiki]

When exactly does she overheat? Highway speeds? City traffic? Idling?

Does turning the heater on full blast (all the way hot, fan on high) make any difference?

Does the fan turn on when the temp gauge hits the middle?

When was the last time the system was flushed with new coolant?

http://www.autozone.com/autozone/parts/ ... 1620_93208



your thermostat should look like that. (more or less)


If the radiator cap seal is dry rotted, that is a cheap replacement that may or may not help, but I always try to eliminate the cheap parts first.


My 81 was running in the upper half at highway speeds, after a coolant flush it was worse, replacing the thermostat didn't help (the old one was super crusty so it was a worthwhile replacement).

The heater did lower the temp when it started to overheat. Ended up being the radiator. Good luck!

[old blue jeans]

Yeah, the temp stays about halfway, no matter what. I just replaced the sending unit and found this out. The temp gauge was jumping all over the place. Now it stays right in the middle. Seems like I may have been running just a bit hot for a while now, depending on when the sending unit went to the pots. Just got the thermostat in. Gonna replace the cap, too. Hopefully, that's all. I guess the next thing is a new radiator. Hope this is done today. Also, there was a recent flush on the coolant. So, I'm hoping that something just got moved around. We'll see....

[old blue jeans]

Ah..... the fan.... why did I miss that?? Thanks so much for your help. It's not coming on. Oh well, a new thermostat can't hurt.

[dlb]

easy test to make sure the fan itself works: with the key in the 'on' position, unplug the connector from the bottom passenger side of the rad. the fan should come on. if it doesn't, the fan itself is faulty. if the fan turns on when you unplug it but it does not come on when your temp gauge gets to the top of the temp icon, the fan switch is faulty.

replacing either is easy but you need to drain the rad if you replace the fan switch.

[keith]

If the temp goes up when you are going uphill, it is the cap.

[Petros]

Check your coolant level first, if it is using coolant you have a leak, bad cap, or a bad head gasket. If it runs cooler when topped up the cause is low coolant level, likely caused by a leak somewhere, possibly the cap, or a leaky hose, or the head gasket. If the coolant is topped up and it still runs hot it could be either the t-stat or the radiator is plugged up, or something else is restricting the coolant flow.

If the t-stat is over 2 years old best replace it anyway. They typically fail like this, slowly causing the car to run hotter and hooter a little at a time each rime you drive it, since it does not open all the way. Do not buy a cheap t-stat (many are junk right out of the box), get the one with a warranty, if possible US or Japanese made, should cost about $16-19. Napa, dealer or others that sell a premium brand are good places to get a new one.

Irowiki has it correct: if you turn on the heater and the temp drops, it means you have limited cooling capacity. So either the t-stat is not opening all the way, or your radiator is clogged up. it could also be possible the lower hose is soft and collapses when you rev the engine, choking off the coolant. After you change the T-stat, if it does not go away, you should have a radiator shop check the temp on the face of the radiator with a heat gun, if it is plugged, it will show as cooler spots on the rad. the home flushes usually are not very effective, I have done a vinegar soak which will pull off some of the scale. If the rad is corroded however, the vinegar will eat through it. that just means it was going to fail sooner or later anyway. Or you can pay the rad shop for a "power flush" with harsh chemicals.

do not just go replacing cooling system comments at random, diagnose it first if possible, start with the cheap stuff and work your way up.

BTW, the fan does nothing above about 30 mph, the air flow above 30 is more than enough to cool it, the fan only comes on when idling or moving very slow in heavy traffic. even the heater fan is usually enough to keep the fan from cycling on. So if it gets hot as speed, it is NOT your fan.

good luck

[old blue jeans]

Welp, I replaced the cap, thermostat, sending unit, burped and topped off the coolant, and put in a new relay and fuse for the fan. The fan does not come on like it did a week ago. The fan would come on at idle and stay on for longer. It comes on intermittently, and seems to only stay on for about 10 seconds.

Tonight on the way home from the parts place, the temp dropped back down to normal and then went right back up. The fan does not come on when I unplug it from the passenger side of the radiator. It also keeps the same temperature than it did before I replaced everything. Still stays right in the middle; on the highway, at a stop light (slight increase), and at 30 mph, or even with the heat running full blast in the car.

The car has always used a little coolant, but not much. I put in one-half pint about every 3000 miles. I sometimes see a few drops on the ground under the car, but nothing to get too upset about. I'd guess that it burns a little and and it leaks a bit, too. One-half pint every 3000 miles doesn't seem so bad for an 85 with 243,000 miles +. But even when the coolant has been low, it's never fallen below the line on the reserve.

Shouldn't the car cool down when I'm on the highway, even if it won't (by way of the fan) at idle?

Thanks for all the tips from everybody, very helpful, and very appreciated.

[old blue jeans]

Ok, so I have a small edit to make on my last post. The fan DOES come on when I unplug it and the key is in the ON position. But I'm still wondering if all of this messing around has also illustrated to me that the radiator is not getting the best circulation. It should cool down on the highway even if the fan switch or fan, is not working. In my case, it seems that one or both are not working, but the temp is still not dropping on the highway.

However, I did see the temp go back down tonight, but only very briefly.

I feel like I'm close.

Thanks again for all the help.

[irowiki]

When the temp is up, crank the heater on max!

[marlinh]

I think it's really important to check actual temperature with a heat gun. I have driven several cars with erratic gauges. Even one that I had to bang on the dash and the needle would drop down. You could be chasing a ghost. If the temperature stays in the middle all the time, that's what's supposed to happen. Only under extreme conditions should it fluctuate, extremely hot day, long steep climb etc. And then it will should stay within operating range.

[old blue jeans]

I Installed a new radiator today, and it sounds great. Miles better than before all this. The old one was just clogged and rusty.

As a side note, however, I found an interesting site that may have a 160 degree thermostat to replace the 180 degree stat if anyone is having problems with overheating, or global warming (living in the south).

http://www.mishimoto.com/

I inquired about a fan switch that may lower the temp the fan clicks on. They don't currently offer one, but they say they'll add the Tercel SR5 to the list.

Thanks for all the help everyone.