jwillman

Got my shift linkage done today and took the car for a spin. Wow what a difference! Dont have to search for gears anymore.

A short time after pulling into the into the driveway I noticed that I had a pool of coolant under the car originating at the coolant bottle over flow.

History is this is the first Texas summer I have been operating the car Both fans are operational and radiator/block has been flushed. I am using G05 at 50/50 with distilled water. I recently got the AC operational and was running it today. OAT was about 102F. I have the heater valve replaced with a pet **** type valve to block off the evaporator. I recently replaced the radiator cap with a OEM from Roger.

The temp idicating system had been a bit flakey in the past. Since owning the car the overtemp light on the gauge has always been illuminated until after fixing the AC when it suddenly went out. Gauge then seemed to read accurate compared to a IR temp gun. Today the light was on again and the gauge never read beyond half way versus second mark 2 weeks ago.

Is it just over serviced with coolant since I have the heater blocked off and blowing out the excess or do I have bigger problem?

What drives the gauge reading and is it also the sensor for the over temp warning light?

Thanks

Mrmerlin

what is the level of the coolant bottle?
it should be just over the seam when its cold.
What color is the coolant bottle you have
whitish clear,
lite tan
dark tan,
brown with cracks

jwillman

Coolant level after over flow and engine cooling off is about 1/2inch below the seam.

Coolant bottle is brown with cracks.

Mrmerlin

install a new coolant bottle

jwillman

Thanks Merlin. For educational purposes whats the link? Is the thought that it is not holding system pressure? Would this also affect general system cooling efficiency as well?

What about the coolant gauge issue? Are there two different sensors for gauge and overheat warning?

fraggle

Yes there are two different sensors for overheat light vs the lamp.

After you replace the tank, put in some water wetter as well. It will help.

Mrmerlin

the coolant tank has its own level sensor, the bottle being cracked means it may not hold pressure replace the bottle,
road test,
then report back

jwillman

Any idea which sensor is which? I see three on the water bridge of my spare engine. One on the front pointing out and two on the drivers side top front and aft.

I had added some water wetter the last go around when replacing the cap because I had coolant bubbling into the reservoir.

jwillman

I ran the car today in the driveway. No coolant out the drain. About 10 deg difference between hoses and both fans running. Temps were 205/195 F with OAT at about 95 F.

The viscous fan is firm after shut down. I recently deleted the air pump and have a short green belt on the fan that seems very loose but others have verified theirs are as well. I picked up some 10K silicon diff lube at a hobby shop and will try servicing the viscous fan before trying the new coolant reservoir.

Any input on the temp sending unit / overtemp switch location?

Gauge never got to half way today and light was on the entire time. Seems odd both senders would go at the same time. Could it be the a common problem at the cluster?

jpitman2

The front facing horizontal thing in your pic is the thermotime switch, related to cold starting mixture. Not sure which is which of the other two. Check on your car what happens at the gauge when you disconnect one of them...
jp 83 Euro S AT 53k

jwillman

I found the wires for the overtemp sensor contacting each other and spread them out. Overtemp light is out and gauge is reading properly, it appears.

I ran the car tonight and the belt driven fan seems to be fine. Temp climbed to a needle above the second white line. I shut down the car and within seconds heard bubbling into the coolant tank and some over flow. I noticed that I also had air bubbles coming from around the low coolant sensor cap on the bottle. Would a loose cap/ bad seal be enough to cause this issue? I will pull it out this weekend and explore.

dprantl

If there is a big enough leak in the cap to cause a significant pressure drop in the coolant system, then yes you would experience coolant overflowing out of the reservoir at high ambient temps.

Dan
'91 928GT S/C 475hp/460lb.ft

Mrmerlin

the reason for the pressurized system is to keep the coolant from boiling if you remove the cap and you dont hear pressure escaping when its hot then there is a leak and thus the coolant will boil.

Replace the coolant bottle use a fresh O ring to seal the level sensor then connect the bottle back to the system and roadtest,
if with a fresh bottle you still have bubbles coming out of the bottle then you have a leaking headgasket, you could also get a block tester from NAPA and check the coolant for hydrocarbons if you find them then you have a leaking headgasket.
On a car this old if the HGs have not been swapped out you should figure that is something will need to be done

jwillman

Thanks merlin and all. Bubbling through overflow and overboard looks fixed.

I had seen coolant bubbling around the low coolant sensor cap. I pulled the coolant reservoir out today and found the low coolant sensor cap very loose. I had found a much better looking coolant bottle at a local wrecking yard today (no cracks and much whiter) so I swap out the bottle and mad sure all caps and fittings tight. Drove the car, 101deg F OAT, and although temp still goes to the second white line it stays there even with AC running and at a stop light. When back at the house and shut down there is no sign of bubbling or over flow.

Now to pull the belt driven fan and add some silicon oil to see if I get get the operating temp down a bit.