It doesn't make any logical sense to me...

When I'm in traffic it runs nice and cool due to a 180 degree t-stat, 3-core GDI radiator, 2-speed Ford Taurus fan.... but as soon as I hit 50+mph the temp starts rising. It doesn't matter how hard I'm on the throttle... I could be WOT for miles or crusing with it in 5th at 50+mph and the temp will rise but as soon as I drop below 50mph, it cools back down!!!!!!

I changed the t-stat, flushed the system (ran a hose through it), and cleaned out the fins on the radiator (SO MUCH MUD!!!) and the problem disappeared for about a week but now it's back.

I'm thinking it might be weird air pressures behind the radiator at 50+mph...... or it could be running lean, but i've got some exhaust leaks which, I thought, meant it should be running rich due to the presence of extra oxygen. The new manifold and y-pipe should be here today.

Well, after searching and reading more it could be a clogged radiator. Or timing - but I set the timing back to factory a couple months back when I had to smog it.

Thoughts? Suggested tests? I've got a NIB spare water pump (in case it dies on the trail) but I don't think the water pump is the problem.

 

Dont know if this happens to better engineered jap vehicles. But older american cars can overheat at speed because the lower radiater hose will colapse and restrict flow. Thats why they had springs in them.

 

Could be.... will it stay collapsed when I pull over after a 50+mph run?

Any other thoughts? Does it sound like a clogged radiator?

 

If its load related, you can do this test. Find a fairly steep hill, a mile long or so, on which you can run in 1st gear. Try it on a day where ambient is above 85F.

That has always been the worse case for my vehicles, ie: slow speed, steep hill, hot day. Add your lights and anything else which is a load. A properly running system will have no problem, but a bad fan clutch, or leak etc. will show up.

I am assuming you are not losing coolant, right?

 

Correct, as far as I can tell I'm not losing any coolant.

When I flushed and refilled, I ran the motor with the cap off for a bit and squeezed the upper hose to try and burp all the air out. I'll check the level in the radiator and the tank when I get home.

 

I'm not losing any. Any thoughts? I'm about ready to drop the money on a new radiator..... just to throw money/parts at it and hope it solves it cause it doesn't make any logical sense to me.

 

I'm still wondering if its a situation where it requires a load (such as high speed driving, or low speed up a hill for 1/2 mile or so).

You believe you've got circulation. You have no leaks (no engine damage!). You have lots of cooling capacity. Your T-Stat works.

Does the engine run smoothly, no pinging, no rough idle?

Have you considered a hand-held temp sensor? I bought one for $41 dollars, new, about 6 months ago. Besides being fun, it is useful for all kinds of temperature factors.

I'd probably use it to check across the radiator, and in and out, to check radiator function. I'd check the engine for hot spots. I notice my 22rec runs much hotter on the center two pistons... interesting.

Anyway, if the engine is running smoothly, and you are running rich, then that extra energy is being burnt off somewhere. So you are right to wonder about that, seems to me.

If you run from cold, with fan disconnected, at idle, does the warm up cycle work "normally"?

Does Concord require a full smog2 test? If so, any clues there?

 

Take a look inside the radiator if you can. From above look down the passages and see how they look. Beteter yet, drain the rad. and look into the bottom tank with a flashlight. If there are desposits visible along the bottom of the core, then that may be the problem (it was in my case).

My '85 was overheating at speeds > 65 or RPM > 3500 in temps > 75F, drop below any of those limits and it ran perfectly cool. Turned out to be the radiator, replaed it with a 3-row unit and it has been cool now for 9 years:
- http://www.4crawler.com/4Runner.shtml#Engine

 

Hope you figure this out, cause I am having the same problem and cant solve it. Have been through everything in the cooling system (twice) timing is right on, even rebuilt the carb and reinstalled the intake manifold, no joy. If you get yours fixed please post the solution for the rest of us. I am almost to the point of taking it to some else (hate anyone else working on my truck) to see if they can fix it.

 

A friend of mine has an infrared thermometer, I asked him to bring it up here this weekend. I'll check the temps across the radiator.

Using the smell test, I'd say it's running rich. Idle is fine and purrs along.

With the cap off (and thermostat open), I can get on the throttle and watch the coolant start flowing across the opening.

Looking down from the top, there are some white deposits around the edges of the passages. I'll see if I can get a picture of it.




Thanks for all the input guys! I'm really starting to think it's the radiator.

 

Oh, and I've got the new exhaust manifold and y-pipe on. Went through and did all the gaskets and seals in the exhaust system at the same time.

 

New radiator ordered. It's probably on my doorstep right now. I hope this solves it. I'll let y'all know.

 

Sorry for the late reply, however I think the new radiator should resolve the issue. You know airflow isn't the issue, because you have the electric fan. In slow traffic, the engine isn't working hard enough to generate a lot of heat for the radiator to dissipate, so there isn't a problem. However, at speed, the engine is working harder, and doing so continuously, apparantly generating heat faster than the radiator can get rid of it.
My guess is that you have some clogged up tubes or passages in your radiator which reduce its efficiency. If you haven't installed the new radiator yet, try driving until you see the temperature guage begin to climb, then turn ON your heater, with fan and temp set to max. Doing this uses your heater core as a secondary radiator. If the temperature guage begins to go down, you have identified the radiator as the problem.

 

is that two speed ford taurus fan a puller or pusher?

did you do any work on your truck before this had happened?

 

The Taurus fan is a puller. And it's working correctly. Before this started I didn't need it all when I was on the highway.

It started about a year ago... and when I went to diagnose it I pulled the thermostat and when I went to bolt up the housing, it stripped a bolt. Took me a while to get new parts in (read: about 4 months cause I was out of work) and when I put it all back together with the new intake manifold and the new thermostat, the problem was still there. I've been taking it easy on the truck and just driving to work and back (no freeway driving) so it's staying nice and cool until I get over 50 mph. So weird. The new radiator came yesterday. I'm gonna swap it in on monday.

 

let us know how that goes. maybe the rad is clogged up, less flow

 

Swapped the new radiator in yesterday afternoon. I ran the truck real hard up over a couple of the local passes on the highway and the temp was super low and didn't budge.... I'm keeping my fingers crossed that the new radiator solved the problem. I'm planning on doing a two night camping trip up near tahoe this weekend, so I'll see then how it really is running. *scary*