Cooling system trouble

[mckeig]

Thanks for the replies. I'll dig back into it Saturday morning and fingers crossed everything will work.

[KevAndAndi]

https://docs.google.com/file/d/0B3XBQIn ... edit?pli=1

Here's a link with a handy schematic of the cooling system. I think the OP has a good grasp; I'm posting mainly to help orient folks who may read this thread in the future.

[mckeig]

https://docs.google.com/file/d/0B3XBQIn ... edit?pli=1

Here's a link with a handy schematic of the cooling system. I think the OP has a good grasp; I'm posting mainly to help orient folks who may read this thread in the future.

Thanks for the link! I was looking for something like that.

[mckeig]

Okay, I've been working on it today.

I drained everything and started over with filling and burping. I started it up to test, and when it got to 195, the temp came down somewhat when I presumed the thermostat opened. Victory #1. All hoses felt firm and hot, and the lower radiator was hot. One step closer than I was last week to figuring it out.

After that, it steadily increased until about 220, when I shut it off. During the warm up I revved the motor to help move the water. I didn't see a noticeable difference in the speed at which it heated up.

Still no fan at any temp.

After a while, I tried again, this time bypassing the thermo switch and putting the fan on full time.
The temp went up, until presumably the thermostat opened, then dropped momentarily before rising again. Reached 215-220 and stayed there. Fan still running full time. Revving didn't seem to drop it any. I shut it off.

It shouldn't be running at 220 should it?

Tested one more time with the sensor that pegs the needle unplugged. No different results.

My theories at this point:
-Possible a bad thermo switch on radiator, or bad ground. (I tried tracing the ground, but lost it in the harness. Does it connect to that spider on the driver side behind the headlight?) This is additional to the other theories, since with the fan on full time it still sits at 220.
-Possible bad water pump. It does not seem to be moving coolant through the system efficiently.
-Possible blockage somewhere in the system.

What is the likelihood that one of these is the culprit?

Thanks!

[bradartigue]

I doubt it is blockage - I've never seen a blocked system. I've seen bad water pumps, and sure it could be the issue. Generally speaking if you maintain a temperature and that temp is a little high then something is circulating:

- a bad pump (i find they disintegrate over many years) moves coolant inefficiently
- a bad radiator won't cool efficiently (which may be why the bottom of yours does not get hot)

That fan switch isn't hard to diagnose; it also won't work if the bottom of your radiator stays cool.

[fiatfactory]

.

[mckeig]

I doubt it is blockage - I've never seen a blocked system. I've seen bad water pumps, and sure it could be the issue. Generally speaking if you maintain a temperature and that temp is a little high then something is circulating:

- a bad pump (i find they disintegrate over many years) moves coolant inefficiently
- a bad radiator won't cool efficiently (which may be why the bottom of yours does not get hot)

That fan switch isn't hard to diagnose; it also won't work if the bottom of your radiator stays cool.

I find that the bottom of the radiator and lower hose now get hot, since the thermostat started working. I think before there was air trapped that kept the t-stat closed.

What's the best way to diagnose the switch?

[mckeig]

Install a "flushing T" into the line that comes from the cylinder head to the heater core,that will help you get the air out that's trapped in the motor.

like this guy shows in the you tube link...sorry best pic I could find about ten seconds in
https://www.youtube.com/watch?v=_jcjwQXUiiM

SteveC

The highest point on mine is the small line connecting to the jacket on the air intake. If I put the T at the heater hose, will I still need to top off at the small line?

[So Cal Mark]

if the thermostat is open, the temp should not climb to 220 if you have the fan running all of the time. Does the radiator get cold in front of the fan when this is happening? The only place where you can get blockage in the system is the radiator. If the radiator is plugged, the system won't cool even with the fan running.

[mckeig]

if the thermostat is open, the temp should not climb to 220 if you have the fan running all of the time. Does the radiator get cold in front of the fan when this is happening? The only place where you can get blockage in the system is the radiator. If the radiator is plugged, the system won't cool even with the fan running.

That is a good point. I think I'll take the radiator out and have it checked at a shop.

[mckeig]

Hi all,
I've been working on it over the last month, and today fired it up again to test. Haven't solved the problem yet, but I wanted to see if anyone knows where the cooling fan grounds? I can follow the ground wire into a wrapped harness, which looks like it goes back through the firewall. In the wiring diagram, it terminates after the fan switch, so I'm curious why it just doesn't ground up front there somewhere?

I know the blue hot wire to the fan is good, and I can run the fan if I ground it myself. I replaced the thermo fan switch with a new one. The radiator is getting hot where the fan switch is. The temp still climbs with no fan.

Since my last post I've done the following:

pull and flush radiator
back flush block
install flushing T at top of heater hose
replace thermo fan switch
replace water pump
since I was in there...
replace timing belt
replace front crank seal
replace spark plugs

I think that's it. I'm going to continue to try to find air in the system, and figure out why it's still getting hot. I did see when the thermostat opened, and felt that all the hoses were firm and hot. Also hoping to find and check/clean the fan ground if someone has an idea where to look.

Thanks!

[mckeig]

After some burping, I ran again, and the fan came on when it reached just over 220 degrees. It maintained 220 with the fan cycling on, then off for a couple minutes, then on again. After I shut it off this time, I noticed the upper hoses were not firm like the first time. Maybe there is still air in there...

I'm happy the fan came on, but 220 seems high. I would think the needle should ride straight up, like around 195. Is it possible the sensor for the needle should be replaced? I'll keep burping for now.

[So Cal Mark]

the fan should come on at 195. How did you flush the radiator? If you didn't get it rodded out all you've done is replace the dirty water. Flushing it won't unclog the tubes, it only changes the fluid

[mckeig]

the fan should come on at 195. How did you flush the radiator? If you didn't get it rodded out all you've done is replace the dirty water. Flushing it won't unclog the tubes, it only changes the fluid

I flushed at home with a prestone flush fluid. Perhaps it needs more attention, if it looks like the culprit. If fluid doesn't travel through the radiator fast enough, the fan may delay coming on, the temp may not go down fast enough. Seems like these are the symptoms.

[KevAndAndi]

You've done all the right things, so it sounds like the remaining problem is a bad rad.

My rad is original, and I recently replaced the thermo switch for the fan. It comes on at around 200. The temp usually stays at around 195 to 200. Even so, I am considering replacing the radiator. I don't want to push my luck with an item that could ruin my day if its 34-year-old self decides to fail.