Mazdax605 Reader
12/1/09 6:31 p.m.

Hey guys,

On my 78 RX-7 GS which I just re-installed the freshly rebuilt factory engine(12A) I have a coolant leak that is external of the engine. I know this because I have some splashes of coolant on pats of the engine bay,and mostly focused on the passengers(right) side of the engine bay. I have a pressurizer for the radiator,and I have put it on,and pumped it up to 15 psi,and let it sit for a bit while looking for the leak. I can't find it,but I did tighten up the radiator hose connections which are on that side of the bay. It will lose about 3 psi over an hour,but I have no puddles,ar trails of green that I can see in the cooling system.

I know it isn't getting into the engine as I would have a sweet smelling exhaust,and white smoke which I have none of. I also trust the builder of the engine,and doubt the coolant is leaking into the engine,plus the splashing of coolant in the engine bay. It looks as if the engine driven fan is picking up the leak,and blowing it around,but mostly in the right side of the bay.

Any help would be appreciated.


Mazdax605 Reader
12/1/09 9:21 p.m.

So I just checked again,and over three hours I have lost 4 psi on the pressure tester. I still don't see any visible leaks now that the hose clamps have been re-tightened,but I am still losing some pressure. Any help is appreciated.


sevenracer New Reader
12/1/09 9:48 p.m.

In reply to Mazdax605:

You don't say where on the pass side, but I would look very closely at the heater hoses where they go through the firewall and the hose that connects the rad to the heater hard piping. Those get brittle over time.

Also, the 2 o-rings that seal the coolant passages of the intake mani to the block. You should have gotten 2 new ones with your engine rebuild kit. Maybe one isn't seated correctly?

RexSeven Dork
12/1/09 9:52 p.m.

In reply to Mazdax605:

I may be in the area on Saturday or Sunday to pick up an SRI for my MS3 (depends on if it gets sold or not before the weekend). If I do get the part, I could drop by your place and help you find/fix the leak if you like.

Mazdax605 Reader
12/1/09 10:18 p.m.

I have replaced the two heater hoses. The leak seem to be in the area of the radiator. I think maybe the hose clamps were just a bit loose,but I am still concerned that I am losing a few psi over a few hours. The coolant o-rings on the intake manifold were new,and I have never had an issue with them in the past on a rotary,but did on the old L20B in the Datsun this past winter..

It really appears to be an external leak,and if the o-rings were leaking I would think they would leak into the engine a bit,and burn off as white smoke,but maybe I am wrong.


44Dwarf HalfDork
12/2/09 6:21 a.m.

1) Water the motor. 2) Blow dry with exhust from shop vac or compressed air. 3) Spray the cheapest foot anti-fungal spray on motor and all conections. 4) when spray turns white pump up the coolant system. 5) Look for wet spot.

44 PS works great for oil leaks too!

John Brown
John Brown GRM+ Memberand SuperDork
12/2/09 6:42 a.m.

Plus you have the benefit of a fungus free engine.

minimac Dork
12/2/09 7:00 a.m.

Have you checked the heater core ?

Kentetsu New Reader
12/2/09 9:44 a.m.

Is the overflow tank, umm, overflowing?

Mazdax605 Reader
12/2/09 12:55 p.m.

It is not the heater core. The over flow tank is also not the problem,either. I really think it was a few semi-loose clamps,but I stil don't know why I am losing a few psi of pressure,but no visible leaks,or puddles. I had the system pumped up to 15 last night,and when I checked it this morning it still had 11 psi on it. Is that an acceptable amount to lose over 7-8 hours? I remember someone telling me that air can leak out in places the coolant can't. Does that sound right?

benzbaron Reader
12/2/09 2:11 p.m.

I had a wicked little leak in my toyota pickup that was really hard to diagnose. It turned out to be a combination of a pinhole in the cylinder head and a slighly warped exhaust manifold. I don't know if any of that applies to your situation.

Our Preferred Partners