I just bought a bit of a project 87 S4 auto 106K that the top radiator hose gets hot and the bottom doesn't. I checked the thermostat (75c) with the almost boiling water test and it cycles fine and has no sealant on it to interfere with it. The O ring is properly installed, the coolant is as full as I can get it, the radiator doesn't appear to be obstructed inside. When the car is idling and I feel the top hose, it is under some pressure, but the bottom hose is not under any. Both hoses are full of water when squeezed and the coolant flows back and forth through the radiator. I pressurized the system w/ my Stant tester and it held 13psi overnight. Both hoses pressurize with the tester. It almost seems as though the thermo is stuck closed which is causing the pump pressure to back up against the top hose?? Maybe the pumps bad, but I would think both hoses would warm up if that was the case. I going out now to get another T-stat. Please chew on this and throw some ideas my way if you have any thoughts because I don't. Ma brain ahrts. <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />

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87S4 Auto Red
85S Auto White

 

New T-stat didn't work.

 

Perhaps I'm missing something here - does the engine overheat?

The cooling system functions by pumping hot water out of the engine thru the top hose, into the radiator where it is cooled, and back to the engine thru the bottom hose.

It is normal for the bottom hose to be cooler, but usually by only a few degrees.

 

Thanks Wally,
It hasn't overheated. The temp gauge climbs up past the last white mark before the red. I shut it down before it goes any higher. I know the gauges are not to be trusted completely, but I can feel the difference between my 85S and the 87. On the 87 you can hold the bottom hose with no problem, you barely feel any heat at all, but the top hose is too hot to touch. There is a LARGE temp difference between the two. The 85 is like you said, both hoses are at close temps to one another. I plan on connecting a thermocouple into the 87's system tomorrow and seeing what I get for numbers. Thanks again for your help.

Randy

 

Sounds like trouble!

Two possibilities that I can see:
The radiator is plugged. Sounds unlikely, but possible. Pulling both hoses, hooking a water hose to the top and checking for free flow would check that out.
The water pump isn't pumping. Ouch! It is rare but possible for the impeller to come of the pump. It is possible, but rare for the pump to seize - but I would expect belt squeal and smoke from that.

There might be other possibilities, but they are also unlikely, such as a shop rag in the cooling system, etc.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by tresamore:
<strong>Thanks Wally,
I shut it down before it goes any higher.
Randy</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Randy,
I.e. if you did not shut it down, it was running hot?
Did you check the rubber seal behind the thermostat? (The closing seat for the thermostat)
Maybe this is missing, and if that's the case the thermostat cannot reach the seat and cannot close. First when this is closed, the water is forced to go via the radiator.
Another possibility is that the thermostat is working (moving when heated) but not enough to reach the seat.

 

You obviously have a tennis ball stuck in your lower radiator hose.

 

Thanks for the replies,
Wally, I'm going to check the radiator flow w/ a hose today, Im going to borrow a nice 3/16 dia. inspection scope from work tomorrow and have a look around. Erik, that rear seal is a good thought, I had the same problem w/ 2 t-stats and I haven't checked that seal yet, Daah on my part for that one. Old & New, I found 2 ping pong *****, a golf ball and a GI Joe doll head in the lower hose, they seem small enough for the coolant to go around so I didn't think they were an issue <img border="0" title="" alt="[Wink]" src="wink.gif" /> .

 

Mine did that too, and it was a sticking thermostat. (and the new one stuck too) Then, it did it, but not as bad, with the last change , but we think it was air in the system. so, we drilled a pin hole in the thermostat. This helped even more, but I still think there is some air in the system. now that its been a while, I dont see the problem anymore. problem is, the fan wont do anything, because the coolant is not flowing through the radiator. and the fan wont come on anyway, becuase the thermo switch is in the radiator. Its all that themostat. problem, how do we burp the systems to not create this problem.

Mine would also only do this once per day of running. first time out, it would overheat. turn it off for an hour, and come back and race, NO problem. I guess it takes awhile for the heat soaked engine to open the sticking themostat, and then after partially open, it opens and works as normal.

by the way, the bad "new" one , opened up in the hot water bucket, but much slower than a different new one.

go figure.

mk

 

tres -

look at my last post....could it be ANOTHER expansion plug that is working loose???

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=14;t=004872;p=1" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=14;t=004872;p=1</a>

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by mark kibort:
<strong>
&lt;&lt;...&gt;&gt;
Problem is, the fan wont do anything, because the coolant is not flowing through the radiator. and the fan wont come on anyway, becuase the thermo switch is in the radiator.
&lt;&lt;...&gt;&gt;

mk</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Mark--

Are you talking about the Holbert car? My impression on the S4+ fans is that they run off one of the sensors that's in the water manifold, at least in the stock configuration. Is there really a temp sensor on the radiator somewhere?

 

dr bob,
Now you have me curious.
I noticed when my 82's thermostat gave it up the fan did not come on.
Ran a jumper on the side of the road and fan worked. Still overheated though.
When we temporarily fixed - modified with a Black and Decker - the thermostat, the fan operated. Determination was that the sensor, where ever it lives, is on the radiator side of the cooling loop.
Was there a change in location of sensor thru the years?
John S and Pattycakes.

 

Well my radiator flows great with the garden hose. The pump seems to flow OK I guess, who knows whats good or bad, Hi revs = lots of water, idle = little water. The rear t-stat seal was there but the seating surface was quite rough. I'm getting a new one today and trying it tonight. After that its t-belt & pump time I guess. There's some bizarre irony working on an overheating car when its 15° outside. Don't worry its in a heated garage, there will be no cracked aluminum popsicles at my house.

 

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Originally posted by John Struthers:
<strong>dr bob,
Now you have me curious.
I noticed when my 82's thermostat gave it up the fan did not come on.
Ran a jumper on the side of the road and fan worked. Still overheated though.
When we temporarily fixed - modified with a Black and Decker - the thermostat, the fan operated. Determination was that the sensor, where ever it lives, is on the radiator side of the cooling loop.
Was there a change in location of sensor thru the years?
John S and Pattycakes.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">This is a curious for me too. On the S4+, it looks like the fans are controlled from a sensor rather than a switch. There are two sensors on the water manifold, bu I didn't notice any on the radiator itself. Engineering-wise, it makes the most sense to opeate the fans based on the radiator discharge temp. I just don't remember seeing any sensors on the radiator itself.

The FSM mentions that the sensors are dual element type, so the customers for signals would be the two brains, the dash indicator, and the fan controller. At least that's my speculation.

On the earlier cars with the booster fan, the switch is definitely in the radiator. As you pointed out, the fan only worked after you "relieved" the obstruction with the drill, allowing the water to flow down to the switch.

I guess I need to do a little more investigating when I get back home in a week or two. The car is toasty warm in SoCal, while my butt is frozen to a chair near Colorado Springs this week. It's 1F this morning, although the local weather report suggests a low of 14f and a high of 29f today. I'm thinking they need to stick something out in the breeze and see if it breaks off. Most of the plant is suffering from the cold, so we are in a holding pattern until the temp rises to at least 30f. Brrrrrr!

Stay warm!

 

The S4 still has the coolant temp switch on the face of the radiator. It is only one input to the controller.

Check page 19-11 in the manual for the switch location, page 19-15 for its effect.