Lotus Elan and Lotus Elan Plus 2 Forums

Over the past several months, I have carefully reassembled my newly-rebuilt twin-cam engine using the cartridge-style water pump and timing covers from Dave Bean Engineering (which is a story in itself). I've been advised to pressure-test the cooling system to be certain that it holds pressure prior to dropping it in the car. To do that, I:

--Sealed up the water pump and thermostat holes with a hose, a rubber cork, and hose clamps.

--Re-inserted the temperature sender.

--Found an adapter that threads into the hole for the heater valve and adapts it to the fitting for an air conditioning gauge set so I can pressure-test it using a nitrogen bottle.

I do a lot of a/c work, so I'm very accustomed to pressure-testing, peeling the layers of the onion so to speak, finding leaks, fixing them, and achieving the goal of the system not bubbling anywhere when soap solution is sprayed (I use "Big Blu"), holding some set amount of pressure overnight, and not leaking a single PSI. I'm trying to do that here, to reach the point where it can old 20 PSI and not drop at all. As part of this process:

--I found that the threaded neck and threaded plug of the Bean cover were both leaking slightly. I disassembled them and sealed them up, one with Yamabond4 and the other with Permatex Seal+Lock.

--I found that the thermostat neck was leaking due to some corrosion at the flange. I repaired it with epoxy, sanded it, and re-gasketed it and sealed it with Aviation Form-A-Gasket. Below is an example of the big obvious bubbles from this kind of a big obvious leak.



--I found that the temperature sensor was leaking slightly and sealed the threads with Yamabond4.

In doing these things, I've now reached the point where I can pressurize it to 20 PSI, spray soap solution at every flange, seam, and thread, and not see it actively blowing any bubbles or see the pressure drop on the gauge while I'm watching it. Perhaps most importantly, I'm not seeing any bubbles being blown from the interface between the block and backplate, the backplate and outer timing cover, or around the cartridge-style water pump.

If you're waiting for a "however," you're right. There is a "however."

However, if I wait and watch the pressure gauge, the pressure drops by about 2 PSI in about 30 minutes, and if I look very carefully at the sprayed soap solution, I can see some clustering of tiny bubbles (they look like little insect egg cases) in a few places. This kind of clustering is what you learn to look for in a/c work in order to detect very small slow leaks. One place I see them is at the hose connection to the thermostat. That's no big deal; I can re-seal it with a different clamp, and even if it leaks a drop of coolant there, I don't really care. Below is a photo of the tiny bubbles coming from this attached hose.



But if I admit that that's a cluster of bubbles, I have to admit that I see some similar clusters of bubbles at the back of the block at the head gasket. The photo is below.



Note that the block was decked and the head was milled. The head gasket is a layered copper gasket coated with Wellseal as per Miles Wilkins' book and torqued down to spec.

So, while I'd prefer that I test this the way I test a/c systems and reach the point where there's ZERO leakage overnight, have I reached the point where it's good enough? Is it likely that, if there is a small coolant pressure leak through the head gasket, that it'll seal up when the engine heat-cycles a few times?

Thanks.

--Rob Siegel

I find the standard hoses are some what porous through their inner layers and leakage occurs out through their ends between the rubber layers and fabric reinforcement which is what may be happening in your hose photo.

I dont use the standard copper / steel head gaskets as sealing them is challenging especially in race engines and the small leakage you see demonstrates what I believe. I use fibre composite gaskets which seal better and were the technology adopted by most manufacturers after the traditional steel / cooper gaskets were used. The most recent head gasket technology is multilayer steel as made by companies like Cometic but that requires a more ridged head and better machining and is challenging to get to work on a Lotus twincam.

I dont think either of your remaining leaks are critical and probably what most engines have that are built to your specification and generally would not be noticed in service.

cheers
Rohan

Thank you, Rohan.

I think the max operating pressure is around the 10 psi mark, radiator cap pressure release, so you are testing at twice that, maybe this is your intension but 100% above does seem optimistic.

I used to rally a Clan Crusader with a full race Imp engine. The head was Wills ringed and whenever removed and replaced would have a substantial water leak between the head and block (both aluminium). I always put a bottle of Bars Leak fluid into the cooling system and no more leak till the next rebuild. Wonderful stuff!!
Mick

Deleted repeated post

I think you are fine.

Edit, I should say I did the exact same thing with the similar results. I had to "goop" up the bolts on mine as well as the flanges around the pump. I went up to about 10lbs,

Tony

I was thinking that the coolant you are going to put in the system is likely to be rather more viscous than nitrogen gas so, it might not really leak any amount now?

Rob just put the Engine in the Car and see what happens
Alan

Ran when parked? Gordon Sauer

Rob,

I think vxah has good point about viscosity. My background is in the chemical process industry, we pressure tested most systems with water.

Richard Hawkins

RichardHawkins wrote:Rob,

I think vxah has good point about viscosity. My background is in the chemical process industry, we pressure tested most systems with water.

Richard Hawkins

Always pressure test with a no-compressible medium, making a potential bomb is not a good idea.

Pressure ( strength) test with water. Leak test with lower pressure air or nitrogen and soap bubbles. You do both when building petrochemical pressure systems. When building an engine you could leak test with either but if doing with air I would not be surprised by a few small leaks as observed and not worry about them

cheers
Rohan

Folks, just to close this out, with the engine still on the stand, I flipped it upside down and filled it with coolant. This ensured that the passages heading through the head gasket and into the head would be full of coolant, not nitrogen. I then pressurized it to 20 psi and let it sit overnight. In the morning, the edge of the head gasket, where there had been nitrogen bubbles in the soap solution, was dry as a bone. I then flipped the engine right side up and let it sit pressurized until the end of the day. The pressure didn't budge on the gauge, and when I unscrewed the oil drain plug, not a drop of coolant came out. So the conjecture that it's easier for the system to leak pressurized nitrogen than pressurized coolant appears to be true.

So, after nearly six years, the engine is going into the car. "The car" is a Europa Twin-Cam Special. I was posting in this forum because the twin-cam knowledge is deeper than in the Europa forum, but I'll probably hop back over there now. Thanks everyone for your comments and advice. They were hugely appreciated.

--Rob Siegel

Rob,

Air/nitrogen is much less dense and a much smaller molecules than water or glycol. The gaskets and the cast/machined surfaces allow air to weep across the sealing surfaces. Sounds like things are a go.

regards,
Dan