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Coolant system pressure test result data


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Per the Macartney book, Cooling System chapter, it recommends to try the following:

* Pressurize system with coolant system tester to ~ 20 psi and check for leaks

* Leave at this pressure for 20 minutes and note any significant loss of pressure

* Turn on the car with the system pressurized to ~15psi - note the pressure after 10 mins

* Pressure test the radiator cap

My results are:

* Leaking at two hoses - tightened up the clamps no more leaks.

* After 15 mins the pressure has dropped about 3 - 4 psi

* With the system pressure at 15 psi after about 5 mins it climbs to 22 - 23 psi - would this be a definitive indication of head gasket failure / cracked cylinder head?

* Radiator cap relief pressures is at about 15 - 16 psi.

My compression test results are: 130 / 125 / 130 / 130 psi

I do not have access to a leak down tester so I haven't done this yet.

If you've run similar tests on your car, what do you get?

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back up please;


have you been adding coolent?

any abnormal steam out the exhaust with warm motor?

color of oil ?

color of coolent?

temperature gauge behavior?

pinging? gurgling noises ?

heater blowing COLD with hot motor

and then suddenly blowing hot,

then turning cold agin - irraticly?

cooling system pressure will climb after hot

shut off ( "heat soak" ) and then gradually

go down as the motor cools -

your compression readings are at the NOMINAL

Min. ! = suggest retesting hot, and with another

gauge - be sure throttle is held WIDE OPEN

and battery & starter are spinning with gusto.

'86 R65 650cc #6128390 22,000m
'64 R27 250cc #383851 18,000m
'11 FORD Transit #T058971 28,000m "Truckette"
'13 500 ABARTH #DT600282 6,666m "TAZIO"

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How can it climb to 23 pisg with a 15 psig cap? You wann burst your heater core or someting else? I think a 13 psig cap is stock.

A radiator shop is a good place to take a leak.


I have no idea what I'm doing but I know I'm really good at it.

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Car: 1973 tii

Location: San Diego

Recent work: Re-cored radiator and rebuilt distributor

Temp gauge: 1/2 - 5 /8 gauge cruising at highway speeds; creeps up to 3/4 gauge during stop and go traffic

Filled with generic antifreeze (ethylene glycol) and water ~ 50 / 50 mixture

Burped the radiator by lifting the car, turning on the heater, and pressing the lines to get the air bubbles out - sitting at idle temp gauge is at about 5/8.

Thermostat 80 deg. C

Water Pump: BMW original by way of SSF distributors replaced about a year ago

Oil appears fine - it's fairly standard looking - no water contamination from what I can tell just from the dipstick - haven't drained it yet, plan on changing oil/filter next weekend.

Coolant is clean - it was new when put in last week, never had to add any.

Car runs well (I've only driven my tii so what do I know what well is - but it's running better than it has since I can remember), although the AFR gauge reads a bit lean (15.5) at cruising speeds, drops to about 14.5 at idle, and the spark plugs are a bit white. I've timed it to spec, no pinging, has ample power, set the gap (still running points), valves adjusted a couple of months ago. No steam out of the pipe, just the blue smoke on blow-by at highway speeds.

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that coolant system tester, I assume that's the one that replaces the radiator cap ?? So, when running, there is no 15psi radiator cap in place to relieve pressure, so pressure will climb to whatever it wants to.

System pressure will definitely increase as the engine gets hot. First indication of problem(s) is losing lots of water. If you are holding pressure and not losing water, seems normal to me.



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The pressure went high probably because there was no expansion volume in the top tank (too much coolant). It was running with no pressure relief capability.

A radiator shop is a good place to take a leak.


I have no idea what I'm doing but I know I'm really good at it.

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  • 4 weeks later...

I agree with the above - I'm just wondering what angle Macartney was approaching when he recommended testing for this condition. Perhaps there was a divergence between his test equipment and mine.

I've been driving the car for the last couple of weeks and although it does peak up to about 3/4 level in traffic it has stabilized at the 5/8 level.

In the mean time I've tuned my fuel injection to get readings in the mid 13 range at cruising speeds. I want to do a couple of weeks at this level and monitor my mileage and plugs.

Timing is set to ~11 deg. at idle. 10 - 12 deg was recommended by the distributor's rebuilder and I'd like to keep at this for at least a few months.

I guess for this thread - not much of a conclusion yet. Still monitoring the temperature levels, and when I see it rise to 3/4, I turn on the heater. It's been chilly in SD anyway. If something comes up, I'll update.

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