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Thread: thermostat or water pump?

  1. #1
    Fellow Frogger! Wintermute's Avatar
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    Default thermostat or water pump?

    The latest saga in the cooling system of the S16. Made it to Coffs Harbour and back without any dramas. Parked the car for two days and the next drive (for less that 10KM) it started to shoot up close to 110 deg.

    On checking the radiator was pretty much cold. I thought it was out of water so took off the cap but then coolant bubbled up and out.. Quickly put the cap back on.

    Drove home and opened bleed screws to remove pressure, took off the cap and added some coolant... it then proceeded to spill out... after opening the main radiator bleed screw the coolant fell dramatically, figured there was an air lock and did a full system bleed.

    idled for a good 10 minutes fans cycled, no problems.

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    Next day went for another drive and started heading to 110 again when idling. Fans were working properly. found that revving the engine brought the temp back down again (radiator cold, after revving it was hot and temp came down).

    So I'm figuring either the thermostat is not opening properly, or I have reduced flow from my water pump.

    I guess I should just change the thermostat as a first step. I've had plenty fail but this is a bit different to previous times. usually (with this car) when they are on the way out the car won't get up to temp properly, but will overheat on a hot day. This is getting up to temp quickly and once there if idling overheats.

    edit: oh it's a new radiator too, and has only ever for the life of the vehicle run proper 33% glycol and been changed every two years.

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

  2. #2
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    Does sound strange. Radiator staying cold sounds like thermostat; maybe revving the engine builds up enough pressure to lift the thermostat off its seat??

    Not clear from what you described, but is air maybe getting in (apart from when you take the cap off)? Head gasket's OK by the sounds of it. Long shot, but could there be a one-way leak (acting like a reed valve) on the low pressure side of the pump? This would let an air lock build up, while having no telltale drip on the ground. Perhaps give the system a really good bleed, drive for a bit, and bleed again to see if any air has materialised.

    That said, thermostat still sounds like #1 suspect to me.

    Have fun,

    Rob.

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    As a rule a correctly working thermostat should be able to be removed with system hot and hold the pressure. (using a rag over the top of course)
    If coolant is gushing out after the initial release then its time for a new thermostat
    The pump must be ok if eng. cools after a small rev, although plastic impellers have been known to come loose on the shaft (would need a lot of overheating IMHO

    Alain

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    Thanks Ron and Alain! I've had just about every possible problem with the cooling system over the years, but this was different to any previous ones I'll check the level after the car has cooled down (was doing it again today).

    Pretty sure head gasget is ok (touch wood). Thermostat is a bit of a pain but not too hard to do. Will probably be a couple of weeks before I can do it, but at least my normal daily driving only sees the car just getting up to temp

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    Cold radiator is a clear sign that coolant is not circulating . I would certainly start with the thermostat . It is most likely the cheapest place to start with too

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    1000+ Posts cam85's Avatar
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    Hi Tony

    Does it take the 'normal' amount of time to get up to temp or is it faster?

    Ive just had the same problem with the Xsara. Thermostat was working but rad was cold and was bubbling out etc. Turned out to be a tiny headgasket failure in the end.
    I would certainly try and work out if its the tstat before driving too much. Mine got hot many times trying to figure out what the issue was (before I bought actually ). That damaged much more of the engine than we thought it could! New followers, cams etc. Im sure yours will not be that bad. I would do a compression test for peice of mind aswell as tstat test. If you do test the tstat make sure you use water straight off the boil and imerse it. The reboil kettle ditch water from vessle and pour again. Often the cup and tstat take out a lot of heat from the water and it will not be hot enough to open
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    Too many posts! JohnW's Avatar
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    I like to hang them in a pan on the stove, with a thermometer, and slowly warm up the water, to see whether the thermostat starts opening according to the temperature rating (they aren't all the same) and opens steadily and fully, and then closes smoothly too. Shock loading with boiling water certainly will tell you if it is dead, but many not reveal poor opening as temperature increases.

    It does smell of thermostat as the first port of call. My CX has been intermittently misbehaving with everything else fine or new, and I have replaced the thermostat, just haven't had a chance to test it enough yet to see whether it is OK again.

    Cheers
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    JohnW

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    Contented Peugeot Driver addo's Avatar
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    Head gasket.

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    Quote Originally Posted by addo View Post
    Head gasket.
    You're likely right, but what's Tony meant to do with your suggestion? if a customer came to you and gave you the description above, would you say "Head gasket" or "Sounds like head gasket"? What would you do next?

    Have fun,

    Rob.

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    1000+ Posts Peter Chisholm's Avatar
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    First off, I'd be very reluctant to drive a car with the symptoms you describe as it could escalate into a very serious problem.

    Second, do the simpler, cheaper things first. Take out the thermostat and test it.

    Thirdly, if the thermostat is okay, try and arrange for a pressure test of the cooling system. It could be the head gasket or another leaky place (hose etc).

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    Contented Peugeot Driver addo's Avatar
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    I'd see him as capable of undertaking compression tests, and possibly having the coolant tested for exhaust gases.

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    1000+ Posts Peter Chisholm's Avatar
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    Quote Originally Posted by addo View Post
    I'd see him as capable of undertaking compression tests, and possibly having the coolant tested for exhaust gases.
    I'd have to arrange for one as I don't have a pressure tester.

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    Peter: Comment crossover. You're responding to addo's response to me. He's talking about a compression tester rather than a cooling system pressure tester.

    Addo: Thanks. Earlier comment was a bit too certain for my liking. If Tony has the gauge then a compression test is surely an easy and wise next step. I'm still not sure thermostat's been eliminated. As Peter said, start with the easier and cheaper things, if you can afford the time.

    So to summarise:

    1. compression test (if gauge available)
    2. check thermostat
    3. take to a garage for (test 1 if no gauge and) combustion products in coolant test
    4. keep watching ...

    If it fails 1 or 3 it's head off -- gasket, crack or whatever. If it passes 1-3 (with a proper HC test, not just a pH test) it's into stage 4, and time for wild speculations (my specialty).

    Have fun,

    Rob.
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    Contented Peugeot Driver addo's Avatar
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    The last faulty thermostat I saw was a Behr, it was on an Alfa and showed the classic "fail safe" symptoms of taking forever to warm up, then running a shade hot in slow speed heavy traffic.

    I always advocate testing thermostats if they are removed, by use of either a double boiler or suspending them in the pot with no contact to sides or base. One needs to check opening temperature, open state at boiling, then the temperature at which they fully close again. Even new thermostats can be faulty.
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    Yes Addo, what you describe above is the usual thermostat failure mode I have had, This is not doing that.
    After a chat with CAM I'm also leaning towards head gasket. If it is the Head Gasget, it is relatively minor (and I suspect it has been going for three years now). I had some mayonaise in the oil filler after I did the gearbox (car sat for a couple of months)... It completely went away. Then again last year (after sitting for a month when I went overseas) (cleared up again)... I suspect the trip to coffs and back has worsened the problem.

    No sign of any steam in the exhaust, oil is clear, no bubbles in the radiator, and no mayonaise, BUT after bleeding the system and two short trips the coolant level was down again so it has to be going somewhere. I filled it again last night, and have driven about 5KM to the station this morning, will check when I get back to the car tonight.

    Peter you are right about not driving it. I shouldn't be. I might need to start catching the bus for a bit till I sort it out.

    I do have a compression tester so can do that (but I expect it won't reveal too much. The last time I had a blown head gasket it was obvious, cranking with radiator cap off shot water 10 feet in the air Whats the normal procedure for the Compression test? all plugs out and crank over 4 times? It's been a long time since I did one!

    I'll probably get yelled at, but I am considering a chemical treatment as a stop gap measure... whilst I've always figured I would rebuild the engine at some point, right now is not a time to be doing it... I'm generally against any sort of additive with magic properties, but I've read a few reports of wynns radiator stop leak working for internal gasket leaks. It seems to be the least evil option... another with good reports was cargo sealup, though the fact you need to flush it out after a short while makes me more wary of it (clogging potential).

    I found one guy with an old peugeot who said he put the wynns in at 287,000KM and that it was still going at over 400,000KM Head Gasket in a bottle? I know I know... - MBWorld.org Forums The comment about black sludge is a little concerning though...

    I guess a test of the coolant would be a good idea before I do anything rash though...

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    Too many posts! JohnW's Avatar
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    Yup, I'd test the coolant first.... I'd be reluctant to use the stuff but, like you say, for short term you do hear the odd good story. I knew a cheapskate who used it in his S**B for years. Depends a bit whether you are going to keep the car or conclude it is worth so little you can throw it away if the stuff doesn't work.
    JohnW

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  17. #17
    1000+ Posts Peter Chisholm's Avatar
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    If you had a cooling system pressure tester you could find out very quickly if there's a leak somewhere or that something else is afoot - such as thermostat etc.

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    1000+ Posts cam85's Avatar
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    As Tony has said we had a chat about his car. Ive just been through this also.

    My coolent system was lressure tested and came up with perfect scores. So its going to be interesting to see what comes of it.

    In regards to the conpression test. From what I remember

    All plugs out (disconnect coil pack )
    Fit comp tester
    Floor the throttle
    Crank it for a few seconds (same for each one)
    Anything else?

    Avoid the goo. It ruined my radiator and left shit all through the cooling system.
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  19. #19
    1000+ Posts Peter Chisholm's Avatar
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    The only time I've used goo has been on old engines that were a bit worn anyway. With an anywhere near decent engine, I'd rather find the exact cause of the problem fix it properly.

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    Me too, just the expense of doing the head at the moment is a bit of a problem, and if I did do it, I'd probably rather also look at the rings as well, which of course adds to the expense, then incidentals like oil pump, bearings, etc etc all start to add up!

    I'm wary of any type of goo, after having had problems (not coolant) with stuff in the past. Cam was your radiator (that blocked up) a new one or the original? also which type of goo was it!?

    Looks like I'll have to bite the bullet, but SWMBO won't be happy about it! I've got the cash, but the last two months it has been leaving the bank account at a rapid rate!

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

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    1000+ Posts Peter Chisholm's Avatar
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    I remember one time when I used some sort of goo it didn't solve the problem. It's a bit hard to remember now but I think the head gasket (as it turned out) started suddenly leaking even more and so I had to turn off the engine before the recommended time expired. The goo didn't do its thing properly and clogged up the radiator.

  22. #22
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    I'll see if I can do the comp test tonight (cylinder not rad) that may give an indication as to in general how tired the motor is too. I shouldn't Jump to conclusions, just saw the gti6 coolant problem thread too, and someone posted that they had a similar issue and it was just the rad cap... seems unlikely in my case (for coolant loss) but I guess not completely out of the realms of possibility (combined with a sticky thermostat). Still I really think I would see some coolant if that were the case.

    BTW I did mean to post before that I do want to keep the car. The idea of goo was to buy some time (assuming the latest stuff doesn't do harm). Another one that possibly sounds too good to be true is the K-Seal Using a Head Gasket Sealer | K-Seal Engine Treatment

    Tony.

    Tony.
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    Morris 1100 1965 green

  23. #23
    1000+ Posts Peter Chisholm's Avatar
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    I also remember a 504 many years ago that had a very hard to track down coolant leak. It turned out to be a minute hole in one of the big welsh plugs at the back of the head. It didn't leak every time but when it did, all the coolant dried off because the engine was hot which meant that there was no trace of the leak.

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    One more datapoint I need to do the thermostat as a first thing as already mentioned.

    Checked coolant when I got to the car. Semed to be exactly the right level. Drove home via the supermarket. Got up to temp normally, parked the car with it just creeping over 90. came back started and back to 90. Drove about 400M and temp started to head to about 1/2 way between 90 and 110. Turned a corner and the temp gauge dropped back almost instantly to 90 deg. Got home and idled in the driveway for a few minutes and sat on 90... So it seems like a possibility the thermostat is sticking.

    It doesn't explain the coolant loss unless it has been venting under pressure when hotter than normal (or I had air that I didn't get out when I bled it the first time).

    Tony.
    306 S16 1995 black
    Morris 1100 1965 green

  25. #25
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    Quote Originally Posted by Wintermute View Post
    One more datapoint I need to do the thermostat as a first thing as already mentioned. Checked coolant when I got to the car. Semed to be exactly the right level. Drove home via the supermarket. Got up to temp normally, parked the car with it just creeping over 90. came back started and back to 90. Drove about 400M and temp started to head to about 1/2 way between 90 and 110. Turned a corner and the temp gauge dropped back almost instantly to 90 deg. Got home and idled in the driveway for a few minutes and sat on 90... So it seems like a possibility the thermostat is sticking. It doesn't explain the coolant loss unless it has been venting under pressure when hotter than normal (or I had air that I didn't get out when I bled it the first time). Tony.
    Fingers crossed.... Our 306 and Xantia sit on about 80 degrees or just over, or a few more degrees with AC on during a baking hot day. Never 90. But of course it depends on the thermostat fitted as well.
    JohnW

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