Wedge TR-7 radiator cap

D

Dale

Jedi Knight

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• Oct 19, 2002

• #1

I have added a recovery bottle to my 7's cooling system, because it was blowing out a little coolant each time I got it hot. now it's blowing the coolant into the bottle but it won't draw it back when it cools. It seems that there is always pressure in the header tank even when cold, as I release the cap it blows bubbles into the recovery bottle.( rather rude don't you think) I know this system wasn't designed with the recovery bottle but it seems to make sense as the Spitfire uses the sme radiator cap and they have the catch bottle from the factory I believe. Any ideas? Dale

 

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Dale

Jedi Knight

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• Oct 20, 2002

• #2

Thanks for your reply! I am using a pressure botlle from an older 7 for a recovery bottle but have removed all sealing from the cap so it vents both through the cap and the overflow at the neck.The pressure cap on the header tank is new and has the rubber seal. Maybe it shouldn't have as the system remains pressured all the time even when cool. Before I left for home at noon I filled the header tank completly full and deliberatly filled the line from its neck to the bottom of the catch bottle. My thinking here is that with no air in the system it might function as I think it should. Previously I was filling the header tank to the specified level of 1" below the filler neck. The trip home is a short one so I left it idle 'til the temp came up but it didn't get hot enough to push any coolant to the recovery tank. Guess I'll have to go for a drive and lug it some though as long as the coolant level is up it doesn't get really hot. Thanks again for your response. Take care. Dale

 

J

Joe Litefoot

Member

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• Oct 21, 2002

• #3

Dale,
Two things; first the catch tank needs to be able to breath, do not use a pressure cap on it.
Second; the radiator cap must be the modern type that has a rubber seal under the lid.
Hope this helps.
Joe

 

M

MDCanaday

Jedi Knight

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• Oct 25, 2002

• #4

Dale, coolant loss on a 7 can be the first sign of a failing head gasket. Re-torque the head NOW!!!!Neveer let a 7 get hot!!!! they just cant take the heat. I hope a new rad cap helps, but check the whole system over carefully for problems.Pay attention to the weep hole for the water pump(pass side under the intake manifold) the pump is internal and weeps if its failing( like you will when you price the new one!)
Good luck
Mark(mad dog)

 

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Dale

Jedi Knight

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• Oct 26, 2002

• #5

Hello again Mark!
This puppy hasn't been overheated since the rebuild 5000 miles ago. Head has been retorqued religiously. New water pump (12 Vane)when rebuilt. Really no problems except the coolant recovery tank which I added doesn't act like I think it should. Haven't driven it much since I tried filling the header tank all the way to the top and purging the air from the line to the coolant recovery bottle. I don't think about it unless the coolant level light stays on which it hasn't since I did the aforementioned. Think I'll give up and just drive and enjoy it.

 

M

MDCanaday

Jedi Knight

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• Oct 27, 2002

• #6

Glad you're on top of the little things!! If the cap is good, it should bleed off excess coolant into the tank. Then if the hose reaches the bottom of the resevior, it should allow the coolant to be drawn back up into the system when it cools. This is how it should work, but if there is a problem with the serge tank, for instance a burr on the seat of the cap, whole process goes astray. I have had the situation where the cap was not right for the radiator this led to severe problems. How are the electric fans working??, or are you strictly going manual fan
good luck Mark

 

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Dale

Jedi Knight

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• Oct 27, 2002

• #7

Hi Guy!
Haven't looked under the hood for a couple days but the coolant level light still goes out shortly after startup. No electric fans, it's a thought though as there's plenty of room on both sides of the radiator now that all the AC stuff has been removed. Have been busy getting parts off the second parts car I picked up and preparing to leave for Phoenix in the AM to claim my TR-3A. Am planning on towing it home with the rear wheels on the ground, hope I don't have to disconnect the driveshaft. Thanks for your help. Dale

 

coldplugs

Darth Vader

Platinum

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• Oct 27, 2002

• #8

I added a coolant recovery bottle (actually just an old windshield washer bottle) to my Elan and had the same results as you did. It overflowed the coolant (no surprise there...) but wouldn't "recover" it. Replacing the radiator cap with a newer type solved the problem. The original cap would release pressure when the system was hot but would then maintain a vacuum when it cooled. The newer cap had a small brass colored disk in the center of the larger disk (that holds the gasket) that acted as a one-way valve - it allowed coolant to pass from the bottle into the radiator when a vacuum formed. With this setup the bottle needs to be vented. I had to grind some metal off the tabs that latch onto the radiator to get it to fit. I suspect if you bring your cap to a NAPA or similar place and match it up with another of the same pressure rating you'll find one that'll work. Get an indelible marker and write "Made in England" on it if you're concerned with originality.

[ 10-27-2002: Message edited by: coldplugs ]</p>

 

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Dale

Jedi Knight

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• Oct 30, 2002

• #9

Thank you so much for sharing, I was beginning to think that I was way off base for even considering this. The cap I'm using is a non original replace ment that has the vacuum disc in it. My problem seems to be that a vacuum never exsists in the system as even when stone cold there is pressure on the cap until opened then of course everything is nuetral 'til it heats up and builds pressure again. Very interesting as this cap is the same one as for the Spitfire and those that I've seen are equiped from the factory with a recovery system. Will continue to fiddle and let you know what happens though I now have two LBCs that take up my spare time. But , if one takes up all my time what more can two do?

Take care. Dale

 

M

MDCanaday

Jedi Knight

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• Nov 1, 2002

• #10

Dale, Trust a british car to seamingly defy the laws of physics!!!!!. If coolant leaves a closed system, and it then cools off, there HAS to be a vaccum. If there is residual pressure after it has cooled off, (Houston we have a problem,) there simply HAS to be a source of this pressure.
Perhaps a bleed-down test of the cylinders may reveal a gremlin(hope I'm wrong) I have seen a fair number of rebuilt 7's have problems too soon.
How was the tr3 tow job??
Mark

 

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Dale

Jedi Knight

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• Nov 1, 2002

• #11

Hi Guy!
Gosh I know your right about the pressure having to come from somewhere but it is unthinkable that the head gasket is leaking and cylinder pressure is the source. And how is it that it always stops on the same piston stroke on the same cylinder? Maybe that's not a sound theory but darn it the thing just does everything that it's supposed to do and flawlessly except for this detail. Oh well if I sell the 3 I'll have cash to spend on the 7. For more on the 3 check out my latest post under And the winner is.
Since then I have been under the 3 finding many indications of its having been done by committee to a deadline. All in all though it is a pretty sound car that needs some sorting out. Do you know where I can get a Purolator filter head? This one has stripped threads and will not hold the spin on adaptor securly enough to prevent it from changing its own oil every thirty miles.
Take care and thanks for your input. Dale

 

coldplugs

Darth Vader

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• Nov 1, 2002

• #12

I'm confused. Once the engine is stopped, I can think of only 3 possible sources of "pressure". One is obviously the cooling system itself - this will certainly still have pressure until it cools off. Another is the crankcase, which doesn't seem likely without other symptoms. The last is a cylinder, but this would mean it's sitting at or near TDC with both valves closed. I suppose you could loosen the plugs to relieve this for diagnostic purposes.

My confusion relates to the actual "problem" here. As far as I can tell from previous posts, the only problem is that the coolant doesn't get drawn back into the radiator. If that's the case & it was my car, I'd just keep an eye on the coolant level and make sure it isn't blowing water out the overflow bottle. Obviously I'd watch the temp gauge. After a couple of weeks I'd declare it solved. Did I miss something?

 

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Dale

Jedi Knight

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• Nov 1, 2002

• #13

You sure haven't missed anything John and your probably right that I should just shut up and drive. It's just that when the coolant fills the recovery bottle and the fluid level light stays on I have to remove the cap from the header tank and the recovery bottle and blow into the bottle to push the coolant back into the system. I am terrified at the thought of getting caught doing this and having to explain it to a local authority.

I've even gone so far as to install a tube in a stopper to facilitate the process but this only adds to my fear of discovery by complicating the explanation.

My wife insists that I should be gratified that our TR-7 doesn't suck but this surely stems from her failure to fully understand the situation.

Thanks for putting up with my inane ramblings Dale

 

M

MDCanaday

Jedi Knight

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• Nov 2, 2002

• #14

To clear up coldplugs question, If a headgasket starts to let combustion pressures leak into the coolant system, the pressure will force out coolant past the cap. More coolant than the temp of the motor should have pushed. Then when it cools down, there will still be some residual pressure in the system.(no draw back of coolant) The next stage in this (illness) is that coolant leaks into the affected cylinder, causing white smoke on startup. Finally the cylinder will just fill enough to hydrolock and your all done driving. If it sounds like I have had a sick 7 you have guessed correctly.Actually my folly was getting one for my son to drive to school, then trying to keep it together despite his abuses....which I may some day compile into a book to help other fathers.
Mark

 

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Dale

Jedi Knight

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• Nov 2, 2002

• #15

I know you guys are probably right about the head gasket being the source of pressure but I am still in denial about it as the thing runs beautifully and shows no other symptoms. I will probably put up with it 'til I can get it to KS and get the head off for another go at getting it sealed. I will do a compression test, looking for a cylinder that is lower than the others. Since the coolant doesn't go anywhere except when the thing gets to operating temp. I should probably check comp cold and again warm. Will let you know, but it sure bums me to think that an otherwise perfect rebuild has soured for no apparent reason. Dale

 

coldplugs

Darth Vader

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• Nov 3, 2002

• #16

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by MDCanaday:
To clear up coldplugs question, If a headgasket starts to let combustion pressures leak into the coolant system, the pressure will force out coolant past the cap. More coolant than the temp of the motor should have pushed. Then when it cools down, there will still be some residual pressure in the system.(...<hr></blockquote>

Thanks - your explanation makes sense. Will these engines do this with no other symptoms?

Dale - a compression check is quick & easy & a leakdown test wouldn't hurt.

MDCanaday - don't limit the book to Triumphs and it'll be a best seller fer sure.

 

M

MDCanaday

Jedi Knight

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• Nov 3, 2002

• #17

Dale , dont feel lonely, a good friend of mine once spent big$$ to get a "professionaly" rebuilt motor from California. 2k later the head was on the floor flunking the straightness test. Warped so badly the camshaft was in a bind.In my experience few mechanics are good enough to put a 7 back together correctly. (who checks the cam bores???)They just plane the thing and go.....
For now I suggest some block sealer, and a good hot torqueing this can get you by for a fair long time.
mark(mad dog)

 

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Dale

Jedi Knight

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• Nov 3, 2002

• #18

Hey; I love you guys. You've always got a plan and hope for me. When you say block sealer, Mark do you mean like stopleak or Barsleak? I assume that by torqueing it hot you mean as opposed to waiting 'til it cools. Hadn't thought of that but I've done it on aircooled flatheads that were a problem, will give it a try. We sure thought we had beaten the cylinder head bugs with this one, as we sorted at least 3 heads to get to this one. The second was a head with a very recent rebuild on it that was machined flat OK but when tightened down put the cam in such a bind that a short run time galled the cam bearings. Do you believe that a new factory head is the only safe solution? I still think this engine is unfairly maligned due to improper maintenance and repair. I can't believe that Saab had all these problems for the time they used this engine. Anyway I'll keep driving and enjoying mine and keeping a watchful eye on things. Thanks to all for the good words. Dale

 

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Dale

Jedi Knight

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• Nov 7, 2002

• #19

Will relate todays experiences and see if anyone can glean anything useful from it. Left home at 7 AM for Gallup car running very cool didn't get to normal run temp 'till 15 miles or more out. Nice drive to Gallup and return about a 160 mile round. Stopped for lunch 15 miles from home and noted the recovery bottle full and overflowing a little. Low coolant light flickered some then went out. Stopped again about 5 miles later and the engine was shut down about 15 mins more coolant on ground but header tank cool enough to open slowly. Header tank mostly full of foam. Blew coolant back to header tank from recovery bottle and came on home. Temperature gauge never got to 1/2 way mark all day. Pressure obviously from somewhere not heat related. Must be a slow developement as it took all day to fill the recovery bottle. In retrospect though it has done this before over the same distances. Any thoughts in addition to the excellent input I've already had? Dale

 

T

thegoodbeamer

Jedi Warrior

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• Nov 7, 2002

• #20

Lots of good advise on this subject. I wonder if you have an air lock in the system.Years ago we had one and it drove me up a wall. The cure was to drain the coolant and refill the the coolant with the front end raised.I do this with all my cars when replacing the coolant. Don't know if this is a help but I never experienced this problem again.

Smile as the sun is always shining.