I read that yesterday..there IS no radiator temperature switch.

"Hysteresis" is that feeling you getin the pit of your stomach as you watch your temperature gauge needle rise until it ispointing straightupat your leaking convertible top latch hoses.

Back to dabbing and researching.

 

LOL Touche

 

Update:

I decided to pull the thermostat and check it out in a pot of boiling water. The T-stat begins to open at 84’C. and is fully open at 96’C. (Approx 180’F. to 190’F.).

I also checked the resistance values of the coolant sensors against temperature. There is a chart in the JTIS which provides relative values.

Both items checked out OK.

Finally, I also changed the two major radiator hoses. The logic behind this is sometimes hoses collapse, and restricts flow.

After performing these two procedures, I refilled with antifreeze and checked for leaks. The hose temps on the plastic coolant manifold (immediately after where the coolant leaves the cylinder heads) seemed to be about 20 degrees cooler. Temps there had 185-200 when the high speed fan activated. They are now down around the 180 mark.

To my surprise the low speed fan came on, but the high speed did not. So maybe the T-stat is intermittently failing… and/or the hoses were constricting flow. Either way, the car seems to be running as normal. This is with the original coolant sensor and fan relay installed. Go Figure.

It is much cooler today than when the problem existed, so I am reserving judgement on the fix beening made. However, I think I will replace the thermostat just to be sure.

Gordo

 

Greetings Gordo,

That sounds like progress, and the thermostat is cheap insurance. I like BRUTAL'S idea about pulling the jiggle pin, and there is no harm in doing so anyway.

I mentioned the lower hose because I had seen them collapse before, but your temp reads with the fan on high seemed to rule that out. On one car in particular last summer, I could rev the engine to 2500 RPM when hot and watch the hose suck shut.

The aftermarket hoses I use are much heavier wall thickness, to the extent that you can barely get the factory squeezy clamp around them. I think they come in through a company called Europarts or something like that, but I can get you one if you want an upgrade. A new factory one should hold up for quite a while though. That's the only other information I have to....errr....relay.

 

good read guys, with a little humor intermixed amongst the technical mumbo jumbo.

Andy, seriously, I think a new signature line should be added to your profile -

 

Hey thanks for that Matt,

Most of my jokes are met with complete silence, even when I'm in the same room with people.

Gordo and I go way back. I dare say that repartees like this might actually qualify us as friends... but I'm not meeting him in person until he buys some pants, so parts deliveries to Florida are indefinitely suspendered.

 

I probably assumed operating temps in the high 190's or low 200's were OK, when in fact they were triggering a temp related fault and activating the high speed fans. Since I had replaced the T-stat less than 2k miles ago, I ruled it out as casual. In hindsight, I probably should have double checked the T-stat. By pulling it, I think I caused it to work more freely and it is not sticking now.

But if it were intermittently sticking, it could be the source of this type problem. Today the same spot temp readings on the plastic manifold, just downstream of the sensor, are 175-185, which corresponds better to a T-stat that should be opening at 183.

Also when I changed the radiator hoses, I noticed the lower hose had been installed backwards. As such it was rubbing on the fan shroud and had worn a section of the outer sheath, which undoubted was weakened at that point. It is conceivable the structural integrity of the hose was compromised enough to allow a collapse at that point. If it collapsed sporadically , I would not know about it when I popped the hood to inspect for problems.

I swapped the hoses, and will replace the T-Stat with an OEM unit certified to open at 84'C. Lets hope that ends this saga. gordo

PS AC Line Pressure can trigger High Speed Fans

As an afterthought to anyone reading this thread trying to fix a high speed fan issue. There exists another causal factor totally unrelated to the radiator/engine cooling systems: The AC/climate control. This system has a fault response to excess pressure on the high side which activates the high speed fans. The sensor for AC line pressure is on the aluminum tube which traverses behind the radiator. In the center of this tube is the pressure transducer and connector. In the event of excess pressure, this sensor signals the ECM which in turn activates the high speed fans. This can happen independent of the engine cooling system.

 

An ordo, my other post here went into the twilight zone, but I stated that sticking t stat show no over hear on the gauge, but kick the fans on high, so we put t stats in, along with taking off the little check ball at the top. And anytime the car overheats for anyreason we replace the thermostat cause it seems to damage them. When the hose sucks flat, its the whole thing. Early Jags the stats stuck open, the V8s till the new style multi part t stats stuck closed, now the split the rubber seat on the valve in the t stat and you end up with a p0128 for coolant below threashold, when you take those apart theyre stuck open.....CAN WE NOT JUST GET THEM TO WORK!!!!!

 

What is the reasoning behind removing the check valve ball? and do you remove the metal cage, or just pry it back and take the ball out?