Bad Otterstat, Temp Sender or something else?

[Addy]

Hi Everyone,

My temp gauge isn't getting up past 120 or so. Jumpered the otterstat and the fans came on, but the don't come on otherwise. Is the otterstat purely temperature driven, or does it require that the gauge hit a certain level? Is the temp gauge not getting past 120 indicative of a bad sending unit? It starts at 100/baseline when the vehicle is off, so it's getting a signal of some sort. I'm not seeing any of the random jumping around that others have mentioned when diagnosing cooling issues. I have bled the cooling system using a pressure tester, and the reserve tank is getting hot.

Thanks,

Addy

[Rich]

Good questions. Answers inserted in bold:



My temp gauge isn't getting up past 120 or so. Jumpered the otterstat and the fans came on, but the don't come on otherwise. The fans should eventually engage if the car idles long enough at rest. So they do not go on even then? Is the otterstat purely temperature driven, or does it require that the gauge hit a certain level? Yes, purely temperature-driven Is the temp gauge not getting past 120 indicative of a bad sending unit? Could be bad sender, bad connection, bad gauge. It starts at 100/baseline when the vehicle is off, so it's getting a signal of some sort. I'm not seeing any of the random jumping around that others have mentioned when diagnosing cooling issues. I have bled the cooling system using a pressure tester, and the reserve tank is getting hot.

Additional to answers in bold above:
Try to find/rent an IR temperature gun to see what's really going on temperature-wise. You run the risk of warping a head or otherwise damaging the engine if it overheats. You are not seeing any coolant loss out the overflow tube or other signs of overheating under any driving conditions? And you are not running the A/C? Can you verify that the fans also run when the A/C is on Norm/Max - not that this is any problem, only to verify that when you say they are off they are really off?

[Addy]

Rich,

Thanks for the response.

I started getting a bit of coolant dumping out of the overflow. At that point, I shut things down, not wanting to damage the engine.

A/C is not working properly right now. It cycles on and off, so it's on the list to be addressed later. I'll engage it and see if the fans come on, but I'm fairly certain they didn't. I'll get an IR thermometer in the morning. Where should I be taking the measurement at?

[NightFlyer]

Where should I be taking the measurement at?

Driver's side coolant hoses/pipes - they feed the radiator with the hot coolant from the engine. Passenger side coolant hoses/pipes are the return from the radiator. Just remember that as you're reading the temp through rubber/aluminum, that the actual coolant temp will be higher that whatever the IR thermometer is indicating.

Best luck :thumbup:

[David T]

Make sure the system is filled with coolant and all of the air is out. Make sure you have the otterstadt switch pointed down, the early cars had it up and there was a service bulletin correcting that. You could have a bad switch, they do fail.

[Addy]

Picked up an IR thermometer and took some readings:

Baseline:
Otterstat: 71.9
Tank: 73.5
Radiator: 70.3

Running 2 minutes:
O: 73.4
T: 79.7
R: 70.3

Running 5 minutes:
O: 77.0
T: 92.6
R: 70.3

Fans did not activate during test.

With the tank temp climbing so quickly, and virtually no change at the other 2 locations, maybe stuck thermostat?

[Rich]

1. Run longer idle test. 10min.
2. If tank goes >110C before that then stop.

So far the O'stat has not seen high enough temp to switch fans on so it's not yet proven bad.

Am assuming your IR temps are deg C.

[Bitsyncmaster]

If it's not above 80 F in my garage, I may not see the fans kick on even after a long idle. The coolant flows through the radiator before the fans kick on so you still get cooling without the fans.

[NightFlyer]

The bottle receives a skim of hot engine coolant via the water pump that runs to the heater core when the HVAC mode switch is set to anything other than max A/C. When the HVAC mode switch is set to max A/C, then the hot water valve is pulled shut via a vacuum, cutting off the flow to the heater core, and all the hot engine coolant in the circuit is diverted to the header bottle. Coolant in the bottle is then pulled into the main return line from the radiator, where the hot coolant mixes with the cooled coolant.

While bottle temps will climb faster than the rest of the system, you obviously have a problem somewhere if the overflow is puking coolant, but the rest of the system isn't getting warm enough to trip and cycle the cooling fans on the radiator.

Check the hot water valve, as it could be stuck closed (but that still shouldn't be causing the problem that you're experiencing). Check for line blockage where the coolant bottle connects to the main return line, #1 in the image below, and in the rest of the main return line generally. Also check the cap on the bottle.

IMHO, you're best to drain, flush, and refill the system.

Best luck :thumbup:

http://store.delorean.com/images/Category/large/1-3-2.gif

[Addy]

Ran idle test again. After about 8 minutes, a trickle of coolant came out of the overflow hose. Tank surface temp was about 130F.

Thanks for everyone's help.

[DMCMW Dave]

Hi Everyone,

My temp gauge isn't getting up past 120 or so. Jumpered the otterstat and the fans came on, but the don't come on otherwise. Is the otterstat purely temperature driven, or does it require that the gauge hit a certain level? Is the temp gauge not getting past 120 indicative of a bad sending unit? It starts at 100/baseline when the vehicle is off, so it's getting a signal of some sort. I'm not seeing any of the random jumping around that others have mentioned when diagnosing cooling issues. I have bled the cooling system using a pressure tester, and the reserve tank is getting hot.

Thanks,

Addy

The otterstat/fans are in no way connected to the gauge. They are independent and not calibrated to each other either.

Bad gauge or bad sender. If the sender is disconnected the gauge will read straight up.

[NightFlyer]

Just wanted to note - if the system is overfilled, then it will puke coolant naturally until it finds its equilibrium.

[Addy]

The otterstat/fans are in no way connected to the gauge. They are independent and not calibrated to each other either.

Bad gauge or bad sender. If the sender is disconnected the gauge will read straight up.

Thanks, this is a big part of what I was wondering.


Just wanted to note - if the system is overfilled, then it will puke coolant naturally until it finds its equilibrium.

What defines overfilled? I'm sure I'm there, as I've been replacing whatever it pukes out.

Checked the service records from the PO, and it looks like a service on the cooling system was done about 3000 miles ago, but that was 2006. Flush and refill is starting to sound like my best option.

[NightFlyer]

What defines overfilled? I'm sure I'm there, as I've been replacing whatever it pukes out.

Checked the service records from the PO, and it looks like a service on the cooling system was done about 3000 miles ago, but that was 2006. Flush and refill is starting to sound like my best option.

The system will puke coolant for one of three reasons:

1) Overfilled - in excess of 11.0 liters / 2.9 gallons

2) Overheating - you don't want this to happen

3) A bad cap on the bottle preventing proper pressurization of the system (possibly in conjunction with a poor coolant/water mixture) - 15psi.

Definitely time to get that 8 year old coolant out - especially if it's the green stuff (if it were orange, Dexcool, running old coolant isn't as bad (Dexcool is gentler on aluminum alloys), but still not good).

[Addy]

Got the wire unhooked from the temp sender. The gauge spikes to max when grounded, so it's working right? Safe to assume sender is the cause of my original problem?

[Rich]

What defines overfilled? I'm sure I'm there, as I've been replacing whatever it pukes out.

When cold a full system on a D will be about halfway down the coolant tank.

When the engine is fully warmed the tank will become quite full due to pressure and expansion effects. If you overfill then the excess will flow out as it should, after which time the system will, by definition, be full.

And unless you have a leak it will then stay like that for a long, long time, thus no need to replace whatever pukes out the overflow.

[Addy]

When cold a full system on a D will be about halfway down the coolant tank.

When the engine is fully warmed the tank will become quite full due to pressure and expansion effects. If you overfill then the excess will flow out as it should, after which time the system will, by definition, be full.

And unless you have a leak it will then stay like that for a long, long time, thus no need to replace whatever pukes out the overflow.

Thanks Rich. This is the type of description I was looking for.