Coolant system pressure testing

[sweetp01569]

I don't have a question or a concern at the moment, but just wanted to say how much I appreciate this discussion board and the decades of experience by all the Delorean owners and enthusiasts here!

I had my coolant system hoses replaced with silicon a couple of years ago, with the garage double checking the clamp tightening over a couple of following maintenance visits. However, over the last several months, I discovered that the level of coolant in the bottle always seems to be low (more like a 1/3 full instead of 1/2 full), and topping off the fluid before each ride. After putting more than a gallon of coolant in the car over the last several months to top the bottle off at 1/2 full, I realized I had a problem. The car never overheated, nor were there any visible coolant leaks (no dripping onto garage floor, or anything easily visible.

I had purchased a pressure tester kit several years ago, but did not use it until this past weekend. After looking up a few conversations on this site, I was able confidently use the test kit, first checking the cap, which held pressure properly, and released pressure at 16 psi. I then pressurized the entire system, and it appeared to hold tight at 15 psi, but I then pushed it to 16. Then to my surprise, coolant started dripping, and then pouring rather steadily, from the steel plate under the gas tank. I removed the plate, thinking it may be from a hose connection on the long pipe run. That was dry. Further investigation tracked the leak to one of the smaller hose connections to the heater core, accessed via the panel in the spare tire well, near the fuel pump. At first, I was fearing that my pushing the pressure to 16 psi may have ruptured the heater core (which I changed once in the past, and never want to do again!). However, and luckily, I just needed to tighten the clamp on the silicon hose connection to the core. Once I tightened that, I pressurized the system again to 16 psi, and it held tight for over 30 minutes!

The topside of the tank plate was all rusted, where I expect the leak was occurring for those several months, dripping down to the area between the tank and steel plate, being absorbed by the padding on the plate, and never becoming visible as a drip onto the ground. The coolant being hot probably evaporated partially also, preventing the leak from being easily visible. Pressure testing while cold made all the difference, and made purchasing that kit well worth it! While being discouraged that the system leaked during the test, I know it was for the best as I would never have found that leak easily otherwise!

I know I am probably not saying anything that most of the owners are already aware of, but I wanted to express my excitement about diagnosing this myself and for the valuable information in this discussion board! Thanks again!

[glowof1000suns]

Thank you for sharing! I have a similar issue - seemingly disappearing coolant. I pressure tested the system a couple of years ago, and I could see the needle drop ever so slowly, but couldn't find a leak. I just figured it wasn't holding a good seal at the overflow tank. But now I'm going to pop off my gas tank plate to see if it's the same thing.

[Emit]

When restoring my car I noticed a lot of pitting in the aluminum pipes, water creeps out as the rubber can't get a good seal, sanding out the pits was only so effective because the pits were deep. So it's on my list to replace the pipes, however it got me thinking...

Why don't we replace the run under the car with single length rubber hoses? You'd take out 6ish connections in inaccessible locations that are prone to leaking, do the pipes offer some benefit that a hose would not?

[sweetp01569]

Thank you for sharing! I have a similar issue - seemingly disappearing coolant. I pressure tested the system a couple of years ago, and I could see the needle drop ever so slowly, but couldn't find a leak. I just figured it wasn't holding a good seal at the overflow tank. But now I'm going to pop off my gas tank plate to see if it's the same thing.

Removing the tank plate may indicate leaking in the hose connections just above, or as in my case, at the heater core connections near the fuel pump, especially if you see moisture and rust on the top side of the plate. In my case, the coolant was evidently just dripping down and settling on that steel plate, as evident by the rusted metal and deteriorated pad that cushioned the plate against the tank. I suggest you buy or rent the pressure tester again, and pressurize the system (no higher than 15 psi), and actively look for a drip or weeping connection, wherever you can see or feel them. I'd also test the cap with the tester, which should hold the 15 psi. Perhaps that is your issue, which would be simple to fix. However, you did say the system itself was dropping slowly in pressure, which points to a leak somewhere.

[Timeless]

When restoring my car I noticed a lot of pitting in the aluminum pipes, water creeps out as the rubber can't get a good seal, sanding out the pits was only so effective because the pits were deep. So it's on my list to replace the pipes, however it got me thinking...

Why don't we replace the run under the car with single length rubber hoses? You'd take out 6ish connections in inaccessible locations that are prone to leaking, do the pipes offer some benefit that a hose would not?
Risk of rubber expanding, contracting, sagging plus more rubber exposed to potential damage from road debris other other causes of punctures.

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[David T]

The right silicone hoses and the correct type clamps for silicone hoses will not require re tightening. This is especially important for the hoses under the intake manifold because you just can't get to them to re tighten without removing the intake manifold. A leak under the intake manifold is difficult-to-impossible to see. The coolant will fill the recesses in the top of the block and the heat from the motor will evaporate the coolant leaving behind a golden colored sand which, with moisture, will eventually rot the top of the block causing a massive oil leak. If you have to keep topping off your coolant you have a leak. Pressure testing, putting 15 psi on the cooling system when the motor is cold and watching it for 15-20 minutes, will not only tell you if you have a leak, it can help you find them. Never exceed 15 psi or you risk exploding your radiator. If the motor was ever overheated there is the possibility of a head gasket leak and coolant leaking into one of the cylinders. You can test the coolant for combustion gasses and you can examine the spark plugs for signs of coolant leakage. If your windscreen fogs up that is a sign the heater core is leaking. Check the plastic screen inside the oil fill. If it is melted it is a sign the motor may have been overheated at some point in the past. If you still have the original radiator with the plastic tanks you should replace it with one that has metal tanks. If you still have the plastic header bottle it also should be replaced with a metal one. When checking with a pressure tester make sure where it attaches to the header tank, it is not leaking. The weight of the tester can pull on the adapter causing air to leak out and drop the pressure making you think you have a coolant leak. Use soapy water to check for bubbles. The two weakest systems on the Delorean are the cooling system and the electrical system. On the electrical system you MUST remove the Fan Fail Relay and replace it with either a bypass or an improved relay. If you have an early car there is a bulletin to modify the pipe with the Otterstadt switch so it is on the bottom of the pipe, not the top where an air bubble can get trapped in it and keep it from sensing coolant temperature. Make sure you have either the metal clip or a strap tie to hold the switch in and NEVER use silicone sealer on the silicone seal. Always keep 50/50 soft water and anti-freeze (the good ole green stuff is what you want) in the system and change it every 5 years.