HELP: S52 cooling system high pressure

[Matracer]

I'm facing a problem with my cooling system that I still can't figure out... Basically it's 1989 E30 swapped with a S52 OBD1 with 89 325i radiator. I frequently go to the track with it. 4 weeks ago, I was ending a sessing and the coolant level light was on. however, my level sender connector is not tight, so no big worries. I popped the hood, nd couldn't see well the level so untigthen the reservoir cap to see the level... pressure cme out a bit, level came up a bit, retighten it, everything was fine. (I know I shouldn't have done that but it's done...) Got back on the track for a solid 15min. I popped the hood and the system overpressurized itself and coolant had generously came out off the overflow tube. Also, one of the radiator hose had backed a bit! Note that the temperature was good, sub 200F. I let it cooled for a while, corrected the hose and I went back for a short session, no spill. Return for a longer one, 15min, and it spilled again! I thought the It was really a consequence of me opening the cap... while it was hot....

Drove it as a daily for 3 weeks without any pressure problem or any leak.

Had the coolant chemically CO2 tested and also pressure tested the system at 17psi for 12 hours. No CO2 and not pressure drop. Got it bleeded and put a new coolant reservoir cap. From there, the garage and I were thinking that every was fine.

Got back to the track last Friday and after the second session, a mapple cookie smell was present. Popped the hood and coolant spill was major, from the overflow tube but also from the cap itself! I also could hear a little leak from the coolant reservoir cap. At that point, I tought that it was the fit between my 33 years old reservoir and my new cap, so went back for a session. right after the session checked again and it spilled again, but now it was fuming from the radiator. I check correctly and the was a major leak form the waterpump shaft seal! The pump was replaced last years with a Hig hflow stewart pump. For this to happen, it's defintely not the reservoir, I really have a coolant high pressure problem...! After winding the engine, event when it was at idle, I coud see a significant coolant spray coming out of the pump pulley. Temp was at 188-190F during all the session. Outside temp was pretty cold, and I have a 188F thermostat. I have a VDO temp gauge. The OEM gauge was also looking just ok. so no overheating.



Drove home for 200 miles without the reservoir cap and level stayed perfect and no leak for the pump or anything!

From the CO2 test and the pressure test, my understanding is that it rules out the head gasket and a head crack. So what can cause this high pressure problem? can it only be a clogged radiator? However, the water temp was good... Also, this all started 4 weeks ago when I cacked open my cap while it was hot... I really have no clue!

[pbonsalb]

What kpa cap are you using? I think BMW specifies a 200 with the S52 but some older cars have a 140. Not sure if this is the issue. If you did not bleed properly, maybe that could cause an issue, but if you had not bled properly your temps should be high and yours are fine. That probably rules out air in the system working its way up to the high mount E30 tank. Plus it would have eventually stopped and the problem is persisting. I assume you checked the small hose from the radiator to the expansion tank to make sure it is not blocked (mityvac or or just observe it spraying into tank as the engine heats up).

[Matracer]

What kpa cap are you using? I think BMW specifies a 200 with the S52 but some older cars have a 140. Not sure if this is the issue. If you did not bleed properly, maybe that could cause an issue, but if you had not bled properly your temps should be high and yours are fine. That probably rules out air in the system working its way up to the high mount E30 tank. Plus it would have eventually stopped and the problem is persisting. I assume you checked the small hose from the radiator to the expansion tank to make sure it is not blocked (mityvac or or just observe it spraying into tank as the engine heats up).

I have a 200kpa cap. I haven't checked the small hose yo uare refering to. I will!

[Eric93se]

If your reservoir is any where near that old then its definitley bad. Inside there should be a plastic tube (right side) inside running from the top to the bottom. Over time the plastic gets brittle and shatters, the plastic gets sucked into the engine and the system does not bleed properly anymore and an air pocket forms. When I bought my car the reservior was bad and I did not know at first.

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Also your using an 89 325i radiator on your S52 and your running it on the track, which is crazy.