j.kenzie@sbcglobal.net

Hi guys,
Just venting here (pun). Anyway, I had discovered a PS tank leak in September, and had a new side tank and gaskets installed. I thought I was OK for a couple of months. Then I started getting low coolant warnings. I topped up a few times thinking I had not filled completely, but it continued. I eventually started to see coolant on the PS of my belly pan, right where it had been originally. Shoot. I ordered a used radiator from 928 Int'l. I installed it with new drain plug and bleed nipple. The next day I saw coolant in the same place. Much less, but still present. The side tanks look dry, the top hose looks dry. I am hoping this is the drain plug.
I will put it up on ramps on Saturday and try to see. I was thinking of draining it and putting pipe sealant (plastic compatible) on the drain plug. Any other ideas?
Thanks for listening.
Dave

dr bob

The drain plug seals with an o-ring, so thread sealant will only hurt your cause by fouling the seal surface (recess) where the o-ring seats.

Most better parts stores will 'rent' you a cooling system pressure tester for free, just put up a deposit. Clean everything, let it dry, and add some cold pressure to the system. With things cold, and engine not running, you'll be able to use both eyes and fingers to find any seepage.

On my car, it seems that any leaks in the radiator area eventually funnel down to the drain plug area under the radiator. Don't be shy about checking the radiator for tube leaks, and for seepage at any oil or trans cooler penetrations through the side tanks.

Also, the replacement top hose on my car is thinner rubber than the original, allowing the original clamp to "bottom out" with less than the right amount of pressure. This caused a little bit of seepage under pressure, car ran a little warmer, and eventually allowed the hose to disengage and dump a load of coolant. (!!) Roadside fix and a walk to the market for a few gallons of distilled water. The 'gap' in the clamp wasn't visible, and the torque screwdriver reading said the clamp was tight.

Mrmerlin

FWIW the drain plug gets tightened to snug,
any more than that the head will pop off. always keep a spare handy.

Tank failures usually occur at the top flange of the tank,
otherwise inspect the interior of the hoses that attach at the top of the water bridge,
the little nubs on the bridge will eat into the hoses

j.kenzie@sbcglobal.net

Thanks. Just a question, Dr. Bob. Why is cold pressure better than warm pressure. My system stay warm and pressurized for a while, certainly long enough to look and feel. Does cold pressure give other advantages. Thanks again.
My idea with sealant on the o-ring was to make up for roughness on the surfaces that seals to the new o-ring. Not sure why that would make things worse, but I could easily be wrong.
Thanks again, I will report my findings this weekend.
Also, I am having my repaired radiator looked at again by the shop that tried to fix it before.
Also, I noticed that both original hose clamp's screws have bottomed out on my newer radiator hoses. I will look at the hoses very carefully too.
Dave

Mrmerlin

as Dr Bob pointed out its a good chance the new hoses are quite a bit thinner and the old clamps will not have enough clamping force with the thinner walled hoses,
thus they bottom out before reaching adequate clamping force

j.kenzie@sbcglobal.net

I'll pick up some other clamps that will tighten a bit more. Thansk for the idea.
Dave

dr bob

Cold pressure doesn't burn your hands, can be done easily with the car on stands with pans removed, with garage doors closed to keep the winter out, etc. Coolant that does leak doesn't dry up or evaporate when everything is cold. Fans won't chew off the ends of your fingers, or redistribute leaking coolant for youleaks where heat is a contributor, almost all leaks will be found easily and conveniently with the system cold. If a leak is really slow, leaving the system under pressure while you watch Law and Order: SVU reruns will usually generate enough of a trace to let you find the source.


That's my story, your honor!

j.kenzie@sbcglobal.net

Thanks, Dr. Bob. That was pretty much what I thought. I called my nearby auto store and they have a tester, that I can get on Saturday. In the meantime, I added a generic stainless steel hose clamp on my upper hose, above where the leak is. The factory hose clamp does bottom out pretty easily so it may not be putting much pressure where needed. I thought the clamp might have been designed that way to prevent damage from over-clamping. I didn't know the newer hoses had thinner walls. I have a feeling you may be right about the hose leaking. We will see.
Thanks again to all,
Dave

j.kenzie@sbcglobal.net

Well my extra hose clamp did nothing, so I picked up a pressure tester. I will run test tomorrow. Does 15 psi sound ok?
Thanks
Dave

dr bob

15 PSI absolute max. The cap is rated at 1bar, about 14.5 PSI if you can split the lines. When testing, you don't have the cap as pressure-relief/protection, so go easy.

Interesting tangent-> Several years ago, an enterprising soul in the northeast decided to try and make money selling used 928 parts. He offered a warranty on his stuff similar to what Mark at 928 International offers. A question came to the forum about how customers were testing the used radiators when they got them, and returning them when they wouldn't hold the 1bar relief pressure. He was sure that radiators don't really need to hold that much pressure.


Now, fast-forward to today. How lucky do you feel, and how much do you really want to find out about the cooling system integrity? Were it me, I'd start out with low pressure (a few PSI) and see if I could find any leaks. Fix those, and try again with a little more pressure. Fix any leaks you find. Eventually I'd end up at 1bar, since I really do want that cooling capacity available for our 100º+ days in traffic with full AC load in my black car, without pissing coolant out and/or risk of overheating. Remember that serious hot conditions require that you keep the coolant as liquid. If the system won't hold pressure, not only do you risk coolant loss but also risk erosion and stress damage in areas where the heat input is high enough to boil the coolant locally.

But I'd go slowly.

Another tangent: Marc Thomas used to half-joke that the coolant connection at the heater control valve (the nozzle and the connecting hose) were like a thermal fuse, failing so that the system wouldn't overpressure.

Again, my opinion is that you want to discover all the weak spots and pieces, and fix them now while it's relatively convenient. On the side of the highway, mid-summer heat and a long walk to tools and replacement coolant, not quite so convenient. In my experience anyway.

j.kenzie@sbcglobal.net

Thanks Bob. I am amazed at the breadth and depth of your experience. I will start slowly and see what I find.
Dave

Barry Chan

[QUOTE=dr bob;11131464

Also, the replacement top hose on my car is thinner rubber than the original, allowing the original clamp to "bottom out" with less than the right amount of pressure. This caused a little bit of seepage under pressure, car ran a little warmer, and eventually allowed the hose to disengage and dump a load of coolant. (!!) Roadside fix and a walk to the market for a few gallons of distilled water. The 'gap' in the clamp wasn't visible, and the torque screwdriver reading said the clamp was tight.[/QUOTE]

Why is it the replacement hose thinner?
I just got the top and bottom hoses and they are thinner than what's in the car now and i am holding back a bit before changing them.
I guess its ok to use right and just get different clamps?
Thanks

j.kenzie@sbcglobal.net

Hi again,
Well I got the car up on ramps and pulled the fan shrouds and belly pan. I pumped the cooling system tester up gradually. When I got to 9-10 psi I began to detect wetness at the PS tank seal at the bottom. I cannot see any particular place on the seam where it is originating. The drain plug, trans cooler, and hoses are completely dry. At 10 psi I get about one drop of coolant every 5-10 minutes.
The radiator has a one year warranty, so I plan to contact 928 Int'l with pictures to see what they are willing to do. Any further suggestions? BTW my OEM coolant cap says "100" on it which I assume is one bar or 14.5 psi. I am tempted to order Carl's 7 psi coolant cap, and see what that does.
Thanks for all,
Dave

dr bob

I guess in the 35 years that have gone by, the materials and techniques used to make radiator hoses has improved some. Except for some extra wear-through margin when the power steering belt cuts the lower hose that was installed without the tie around the fan frame, I don't see a problem going with the thinner hose. Plus, I'm not sure you can buy the thicker hose new any more. Even the Genuines are the thinner material now for maybe ten years. I've got a little more than 5 years on mine, maybe 20k miles on a black S4 in Los Angeles. Except for those little teething pains they've been great.

dr bob

Think "previous victim" for perhaps a clearer picture. I wouldn't have paid further attention to the hose wall thickness if I hadn't had the fun of hiking off the freeway for water when mine let go the first time. Windshield full of coolant, with a dash full of coolant-related messages too. I got the hint. Trying to protect others from the same experiences.