I have a 2003 525efi with a 3.3l whipple installed. Closed cooling system losing coolant out of resevoir cap at 4000 rpms or more and then starts to overheat until I stop and fill it back up.. 4000 rpms is about 55 mph. Just made approx 100 mile one way trip home and kept engine under 4000 rpms and never lost a bit coolant. The resevoir has a steady stream of coolant returning from the 3/8 line out of the top of the heat exchanger to the resevoir at higher rpms.
Ive already installed new impellor and housing, no change. Removed heat exchanger and sent to radiator shop, flushed, acid washed and flow tested both fresh water and coolant side, no change. Checked thermostat in a pan on the stove and is working properly. opening at about 120 degrees. Removed impellor housing lines and back flushed. xr drive with low and side water pickup. removed oil cooler end caps flushed and cleaned, removed fuel cooler and powersteering cooler back flushed and all hoses. performed a block test with a chemical to detect exhaust gases. Pressure tested heat exchanger again. all testing ok.
Running out of ideas and warm weather. Any help would be greatly appreciated. Thanks in advance. Dustin

Have you pressure tested the cap? Is it overheating then losing coolant, or losing coolant from pressure, then overheats because of the lack of coolant?

Losing coolant then overheats. Coolant blows out even quicker with cap off. Can pressure test cap tomorrow.
Also motor had complete upper end rebuilt at 400 hrs. 450 hrs now.

i would think head bolts stretching under boost over 4000rpm. did you reuse old or new headbolts.

head gasket starting to go,,i have a diesel in the shop rite now doinf the same thing,,i know this is a gas engine and im working on a diesel but one you have higher compression then most blower engines and once you combine that with 5 psi thats alot of cylinder pressure..pull heads,order cometic gaskets and arp head studs and go to town..i have been chasing this one as well,,it all started when it over heated and the customer put in a new water pump and radiator..around town its ok and once you go on the highway under heavy acceleration it pi ss's out the antifreeze..

that chemical test doo hicky only works if theirs hydro carbon in the antifreeze,in your case its pi ssing out all the antifreeze before it has a chance to show up in the antifreeze..

I'd bet headgaskets also. How much boost are you running??

Not sure if it was done, but like MRFIXXALL said, head studs and cometic or Fel Pro MLS headgaskets. The 525 cam, and compression, will make great power with a blower, but the result is alot of cylinder pressure.

Motor was rebuilt by previous owner. I do not see head bolts on receipt. Felpro 1075 head gasket was used. i bought the boat with 405 hrs and never have had a good run out of it. original owner said he never had a problem?? i was told bost was about 6 psi. gauge does not work but have talked Dustin at whipple.
I've never seen a blown head gasket that has,nt overheated at idle also but this is the first blower motor I,ve dealt with. U would think on a 100 mile run that something would show up?

i dont think the head gasget is completly blown,just weak,but if you keep running it thr gasget will let go,and will no doubt cause other damage,the gasget probibally is not leaking until yo start getting into boost.as already stated,change the gasgets and replace the headbolts with studs,as they do have more clamping power.i like the fel pro mls gasgets,but they require a smooth surface so head&block machining may be required.

the 1075 is a felpro mls gasket,,thay are chit..i had problems with those gaskets in the past on nos motors,,they have a wire ring in them that l limits the sealing around the cylinder and blow out antifreeze out between the head and the block..

like mentioned both sealing serfaces have to look like chrome or they wont seal..as a fact non of the mls gaskets wont seal unless they are real smooth. a way around it is if you spray that blue hitack in a can on them but i dont like glueing engines together..

comedics and head studs,,and get the 12 point nuts so the nuts wont interfere with the headers..


remove the resivour cap,get the engine hot and fill the cylinder with 160 psi of air...if you see the antifreeze bubble out you found your leak..

I gave my cometic gaskets a couple coats of copper kote spray . Painted them, let them dry, installed them. My reasoning was my heads had a very fine RA finish, mirror like, but the block finish was borderline for what cometic recommended . I think cometic now says 50 or 60 RA or finer. Anyhow, no leaks.

I see some of the drag guys actually disassemble the cosmetics and coat each layer. I also use ARP head studs . Only way to go IMO with a blower.

Boost psi is just a number basically measuring the amount of restriction the engine isn't using. With 8.75:1 static, 114LSA with decent lift and duration, that engine is gonna have some cylinder psi , worthy of head studs.

Just guessing but those 525's with whipples are prob 750-800hp mills?