Expansion tank filling fast after engine overhaul

[WhatTheFisaMOT?]

Hey all,

So last year I had a very unfortunate incident where my Sprint blew a hole thru the number one piston. Had a local shop do an engine overhaul with new rings, pistons, bearings, seals and new head gasket. Cylinder head had a once over as well, got the car back and she's running a little rough, but starting better then she ever has. I'm thinking the new rings have increased the vacuum which has exacerbated the leaks in the carbs. But, the thing that puzzles me that it does now is that after the temp gauge hits the halfway mark the expansion tank becomes completely full of coolant, sometimes pouring out, but then my kenlowe fan kicks on and I guess the thermostat opens because the expansion tank goes back to half full and the temp gauge settles between 1/4 and 1/2. I don't remember it behaving this way before the engine overhaul. Any thoughts would be very appreciated.

Thanks, Lukasz

[gmsclassics]

Unless the expansion tank has been overfilled when cold, it shouldn't do this. The level when cold is quite low in the tank as it will expand and fill the tank as the engine gets hot, but not overflow.
The electric radiator fan should be set to come on and go off above the temperature that the thermostat opens. For example, if the thermostat opens at 82 degrees a 'normal' set up would have the fan come on at around 92 and go off at 87 - or thereabouts depending on the fan controller.
Other thoughts:
Have you re-torqued the head yet after the rebuild? Don't leave it too long!
If they changed the thermostat, have they replaced it with the correct type (with foot)? Ditto for the radiator cap.

Geoff

[Toledo Man]

When I bought my Sprint, I was advised to routinely retorque the cylinder head every 5000 miles. Because the engine has been rebuilt, you should be running it in so don't thrash it until you've got a few more miles on it. Because the engine is in "as new" condition, this will highlight weaknesses elsewhere. It might also be an idea to change the engine oil and filter after a few hundred miles. To answer your original question, you might just have an airlock in your cooling system. I second what Geoff has said about the thermostat and the pressure cap. You need the correct items. I'd also go along with retorquing it soon.

[Jon Tilson]

Sounds like you have a mix of issues here.

It is worth a retorque and this would have been done at the first 1000 miles when the car was new. Not sure about subsequent services, but I've never done mine in 50k miles....and all is well.

The footed thermostat is crucial as this seals off or restricts the bypass tube when the car is at running temperature and the stat is open.

To expel air locks open the expansion tank cap when the car cold and gently squeeze the bottom hose and you should expel the air bubbles into the expansion tank and suck back coolant. This only works if the expansion hose inlet into the tank is below the coolant level.

If you dont have bubbles coming out into the tank when the car is running all should be well with the gasket. I have recently had a similar set of issues with another car and in this case it was just a non opening thermostat.

Jonners

[SprintMWU773V]

Obviously back off the studs before re-torquing them.

[Dolly-Nut]

You'd be amazed how quickly they need retorqueing. I'd say do it after the first full heat cycle, then at 100 and 1000.

[Mad Mart]

Just to add my two penneth... The head should be retorqued after initial warm-up, usually the next day when the engine has completely cooled down. Then again after 1000 miles. (nothing to stop you doing it before this time). Make sure the head is torqued down to a minimum of 58 lb ft.

[WhatTheFisaMOT?]

I tried to expel the air, but still the same issue at about 1/2 on the temp gauge the expansion tank fills and overflows. No bubbles while the engine is running, but after I shut it down when the tank is full, bubbles enter the expansion tank.

Sounds like you have a mix of issues here.

It is worth a retorque and this would have been done at the first 1000 miles when the car was new. Not sure about subsequent services, but I've never done mine in 50k miles....and all is well.

The footed thermostat is crucial as this seals off or restricts the bypass tube when the car is at running temperature and the stat is open.

To expel air locks open the expansion tank cap when the car cold and gently squeeze the bottom hose and you should expel the air bubbles into the expansion tank and suck back coolant. This only works if the expansion hose inlet into the tank is below the coolant level.

If you dont have bubbles coming out into the tank when the car is running all should be well with the gasket. I have recently had a similar set of issues with another car and in this case it was just a non opening thermostat.

Jonners

[gmsclassics]

Have you checked the thermostat & radiator cap yet? Have you re-torqued the head?

The clue in your last post is what is happening when you stop the engine. If bubbles then start, that weren't there before, this sounds like you have localised boiling within the engine and the bubbles are in fact steam. I know temperatures are getting high in NYC at this time of year, but this does point to something not right with your cooling system.

A suggestion for running in a hot climate is to run the fan (via a thermoswitch as usual) but from a permanent live (the battery) rather than the ignition feed. That way the fan can continue after the ignition is switched off. I live at the top of a long steep hill and that has solved my issue. However, I while that may help long term, the issue you have needs to be fixed first.

[Jon Tilson]

You still have an air lock....

Heater valve on hot. Let the car cool. Remove expansion tank cap. Make sure coolant level is just above the inlet in the expansion tank.

Repeatedly squeeze as hard as you can on the bottom radiator hose. It should collapse and push fluid and air into the expansion tank from the high point in the system. You should get bubbles out and as the hose expands you suck coolant back in to replace the air. You can also have a look down the filler plug hole and you want to see coolant almost at the base of the filler plug thread.

Try this and also retorque the head if you havent already.

Jonners

[WhatTheFisaMOT?]

Found a new Thermostat and expansion tank cap from a USA parts source for half off, so as soon as they come in I'll install them as well as retorqueing the head. Just curious as to how retorqueing the head can solve a coolant issue?

Also, on a tangent, the shop that did the engine work said they sent the cylinder head to get refurbished and that they'd shave the bottom if it wasn't flat. Now, I see on parts lists that a head gasket is available for the Sprint that is slightly thicker then stock. If the shop did indeed take some metal off the bottom of the cylinder head and a stock thickness head gasket was used, could that be a problem? There is no coolant leaking around the cylinder head as far as I can see.

You still have an air lock....

Heater valve on hot. Let the car cool. Remove expansion tank cap. Make sure coolant level is just above the inlet in the expansion tank.

Repeatedly squeeze as hard as you can on the bottom radiator hose. It should collapse and push fluid and air into the expansion tank from the high point in the system. You should get bubbles out and as the hose expands you suck coolant back in to replace the air. You can also have a look down the filler plug hole and you want to see coolant almost at the base of the filler plug thread.

Try this and also retorque the head if you havent already.

Jonners

[Jon Tilson]

In an ideal world the head would not need a retorque. However dissimilar metals expand and contract at different rates and with
threads involved the net effect can be a light loosening and loss of clamping until it all "settles" and is tight enough to stay that
way under thermal cycles of warming up and cooling down.

Well that's a simplistic view of the science. What you dont want is any loss of seal. If the water jacket is pressurising from compression
in the cylinders then your gasket is blown, but it may be so slight the a retorque will re-seal it.

If it has blown of course its much more likely that a retorque wont reseal it, but its a cheap job that may work.

Thats the thinking....

Yes you are right a thicker gasket may help, but I would only fit one if the head has been skimmed a lot and you can only get crap fuel.
The latter of these is more likely to be true for you state side I guess...

See how you get on.... If you still get pressurising when all else has been done a new head gasket should cure it...

Jonners