Coolant Replacement Confusion

[RamblinDMC]

Hello all,

2203 never ceases to confuse and frustrate me no matter what I'm fixing on it. Arrgghh. Any who, today my dad and I thought it'd be a good idea to drain and replace all of the old coolant as well as replace the old thermostat and otterstat.
After replacing the thermostat and otterstat, we opened the drain spout on the radiator to let what could drain out, and then flush (with the car running) it out with garden hose water (stuck into the coolant overflow tank) until the liquid coming out of the drain spout was clear. It started off with a nice poop brown color and transitioned to a nice clear color soon after.
After as much coolant as possible drained out, we moved the car to a small hill to raise the rear higher to allow more old poop coolant to drain.
We began refilling the car by disconnecting the top engine hose and pouring in about 1.75 gal of coolant/water mixture. After reconnecting that I began adding coolant/water mixture to the overflow tank.
Strangely the car didn't seem to be taking the coolant. It was just boiling out and steaming like crazy. The temperature was a bit higher than normal, but not overheating.
After fooling with that, we concluded that the thermostat wasn't opening. We took out the new one and noticed that there was no coolant in the water pump housing. We poured some more coolant/ water mixture into the flange where the thermostat sits. It took quite a bit of fluid.
Just to be safe we cleaned up the old thermostat and reinstalled it. (It worked before) The car began to pump water again and the temperature was running steady and looked fine. (We could see a steady stream flowing into the tank from the small upper hose, is this from the heater core?) We then opened the purge valve on the thermostat housing to let a small bit of air out. After closing it, looking into the coolant overflow tank seemed to show that the water pump wasn't working again and the temperature quickly shot up. Maybe the thermostat closed back up or another air pocked formed around the water pump, we're getting really frustrated.
What am I missing here? Am I doing something wrong?

[mluder]

The DeLorean cooling system does not have an auto bleed function. You must bleed the system in two places - at the radiator and at the water pump. The intermittent functioning of your system sounds like a classic case of air in the system.

Do you have the workshop manual? It explains how to bleed the system. There's also a how to on this forum called "Burping The Cooling" or something like that.

My preferred method rather than using the running engine is to use a pressure tester. I add coolant to the overflow tank only allowing it to drain into the system. Just keep adding it until it won't seem to take any more and the overflow tank is about half full. Then put the pressure tester kit on and load it up - Don't recall the exact pressure but it's in the workshop manual. Once you have pressure, disconnect the small hose at the top of the rad on the front passenger side and let it purge into a container until the air is out. Put this coolant back into the tank and add as much as needed to get to a half full tank again. Now re pressurize and do it all over again. A few rounds of this should get most of the air out. Now start the car and let it come up to operating temp so the thermostat opens... Then bleed it at the water pump.

Word of caution - if you have the original rad be careful with the hose connection when you bleed. The nipple is plastic and easily broken from removal and re-insertion of the hose. Newer tanks are metal.
Also - Might want to think about getting the bleeding kit that Toby at DeLorean Parts Northwest sells. It's essentially a valve that installs on the radiator hose that makes for much easier bleeding.

Cheers
Steven

[RamblinDMC]

Thanks for the info! That is really helpful.
Oh yes I do have the manual, why I didn't look through it, I have no idea.
For the pressure tester method to work, does the thermostat need to be open or removed?

[mluder]

For the pressure tester method to work, does the thermostat need to be open or removed?

I do it with everything in place. Added benefit of using a pressure tester is you can make sure you don't have any leaks before re-installing the intake manifold, etc.
Auto-Zone in my part of the country "rents" them for free. In other words you pay a $90 (or so) deposit which is refunded when you bring it back.

Cheers
Steven

[DMCMW Dave]

Thanks for the info!
For the pressure tester method to work, does the thermostat need to be open or removed?

No, there is a small bleed valve or port built into the thermostat.

[sdg3205]

+1 for Toby's product. Get the full kit, which includes an auto bleeder from the pump to the header tank.

[RamblinDMC]

I don't really know what happened, but I removed the thermostat to see if the water pump housing was full, and it was. I then started my car and let it run for quite a long time, no overheating. Ran just fine. Even drove it a little. Looks like my problem has fixed itself.
While my car sat overnight, I left the coolant bottle cap off, maybe the air pocket worked itself out.
Now onto other engine issues. It surges while idling and stumbles when revved. Guess I'll start another thread on that.

Thanks!

[mluder]

Looks like my problem has fixed itself.
Thanks!

This rarely is the case. Also, it's unlikely the air bubbles worked their way out of the system. A classic symptom of air pockets is for the car to appear to function normally for a time, then have a major overheat, then work fine again, and so on....
My advice... Follow the coolant bleeding proceedure or you'll find yourself on the side of the road one day. Ask me how I know.

Cheers
Steven