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  1. #1
    Zack
    SAAB SAAB SAAB BLABLABLA Brewmaster's Avatar
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    09 Mar 2011
    Location
    Fort Collins, CO
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    162
    Saab(s)
    1987 900 SPG (totaled), 1987 900 T16 (new SPG)

    Odd overheating problem

    I encountered this yesterday after being forced to go to Denver to pick up a single sheet of paper

    65 degrees outside, 75 mph, heater not on. Temperature steadily rises, fan kicks on. Temperature continues to rise. I'm forced to turn on the heater as the needle nears the top of the gauge. It helps, but I couldn't get it down to even halfway

    Heater blows hot and strong, so I'm pretty sure the tstat is good. Fan kicks on, so I know the hot coolant is reaching the temperature switch. Haven't yet checked the bleed valve

    Anything else I should check? I'm going to bleed it when I get home, but I want to get this resolved as soon as possible as the mountain roads are calling my name

  2. #2
    Sam Carlson
    Tutorial Bot euromobile900's Avatar
    Join Date
    14 Aug 2010
    Location
    Medford, MA
    Posts
    684
    Saab(s)
    '90 900 LPT with a flat-nose conversion
    Well, first you've got to rule out the easy things to spot, like (as you said) air in the system or blown head gasket. I'd think the gauge would fluctuate more if you had air in the system.

    This sounds more like a problem with flow. A stuck thermostat can still allow you to have heat, because unlike most cars, our engines have no warm-up bypass, so the thermostat allows coolant to flow to the heater _more_ when shut than when open. Or it could be that the radiator has some deposits inside it, plugging it up. Or it could be that your water pump impeller is no longer there, due to bad water eating it away. Does it also overheat at idle? To test for a plugged radiator, wait until it gets good and hot, and feel the rad (careful of the fans, which may start at any time!) and if it's hot all over, your radiator is probably working fine.
    Ask me a question about your c900! I promise I either can answer it or know someone who can

  3. #3
    Paul A
    Saab Nut
    Join Date
    11 Mar 2011
    Location
    West London and Wiltshire, UK
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    251
    Saab(s)
    T16 '93 Ruby - T16 '94 Vert Ruby
    I think Euro covered most things above, but my experience tells me you need a new rad. Feeling the rad surface is not always a good test of rad serviceability. I've had this problem on several cars in the past and a new rad always solved it. Don't waste your time flushing it. It will make very little difference. Buy a new rad. Fitting takes two hours, tops. The fact that your heater gets hot suggests that the flow is OK. You can observe flow if you remove reservoir cap when the engine is reasonably hot. Take care to let the pressure escape gradually so it doesn't spurt out. Then rev the engine a bit and you will see the water racing across the resevoir fed by the small vent hose from the rad.

    900s seem to need new rads every 4-5 years unless the cooling system has been well maintained. That means draining every year or so and using distilled or rainwater in the system plus additive.
    Last edited by peva; 12 March 2011 at 16:34.

  4. #4
    Andy Graham
    modérateur
    Join Date
    08 Aug 2010
    Location
    Oz
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    235
    Saab(s)
    '88 vert, '88 Aero
    Hey peva good to see you here old cock.

  5. #5
    Paul A
    Saab Nut
    Join Date
    11 Mar 2011
    Location
    West London and Wiltshire, UK
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    251
    Saab(s)
    T16 '93 Ruby - T16 '94 Vert Ruby
    Quote Originally Posted by SpecialTool View Post
    Hey peva good to see you here old cock.
    Thanks for the welcome from Oz. It may be an old cock but it's not worn out.

  6. #6
    Zack
    SAAB SAAB SAAB BLABLABLA Brewmaster's Avatar
    Join Date
    09 Mar 2011
    Location
    Fort Collins, CO
    Posts
    162
    Saab(s)
    1987 900 SPG (totaled), 1987 900 T16 (new SPG)
    Oddly enough it didn't overheat this weekend. I drove all over the place getting tools and whatnot to reseed my lawn and although it got to 1/2 (something my SPG NEVER did) it never overheated

    I'm going to pull the rad out of the SPG though and check it, keep it on hand just in case

  7. #7
    Paul A
    Saab Nut
    Join Date
    11 Mar 2011
    Location
    West London and Wiltshire, UK
    Posts
    251
    Saab(s)
    T16 '93 Ruby - T16 '94 Vert Ruby
    Engines develop more heat traveling fast than bumbling around town. Driving around town shopping, doing chores, etc, is no test for a cooling system. Driving at speed, say 3-4K rpm is. A lot of the heat developed in an engine comes from internal friction and not only from combustion, so the faster you go the more heat is being developed, even if you have your foot off the throttle with a following wind a lot of heat is being developed. What you say convinces me your rad is clogged and not passing as much as it should. New rad time I'm afraid. You'll find you can drive all day with your foot on the metal and the gauge won't go beyond half way.
    PS Your gauge will only get to half if you have an 89° stat in. An 82° will barely get you off the stop.
    Last edited by peva; 14 March 2011 at 16:56.

  8. #8
    Zack
    SAAB SAAB SAAB BLABLABLA Brewmaster's Avatar
    Join Date
    09 Mar 2011
    Location
    Fort Collins, CO
    Posts
    162
    Saab(s)
    1987 900 SPG (totaled), 1987 900 T16 (new SPG)
    I understand that. I should've clarified though, driving around all day in my area means a lot of freeway time

    Quote Originally Posted by peva View Post
    Engines develop more heat traveling fast than bumbling around town. Driving around town shopping, doing chores, etc, is no test for a cooling system. Driving at speed, say 3-4K rpm is. A lot of the heat developed in an engine comes from internal friction and not only from combustion, so the faster you go the more heat is being developed, even if you have your foot off the throttle with a following wind a lot of heat is being developed. What you say convinces me your rad is clogged and not passing as much as it should. New rad time I'm afraid. You'll find you can drive all day with your foot on the metal and the gauge won't go beyond half way.
    PS Your gauge will only get to half if you have an 89° stat in. An 82° will barely get you off the stop.

  9. #9
    Andy Graham
    modérateur
    Join Date
    08 Aug 2010
    Location
    Oz
    Posts
    235
    Saab(s)
    '88 vert, '88 Aero
    Quote Originally Posted by peva View Post
    Thanks for the welcome from Oz. It may be an old cock but it's not worn out.
    Many a good tune played on an old fiddle!

 

 

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