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I have a 1998 Eldo with about 110,00 miles, second owner, no previous issues to my knowledge no carfax problems, and no problems in the last 3 years since I have owned it other than (3) alternator problems.
I now am experiencing a loss of coolant, it goes about 50 or so miles and the temp gauge goes way up and all the bells and whistles tell me to stop the car, I limp to the side of the road, wait 10 minutes and add about 1-1/2 gallons of water to the surge tank, and go on my merry way. There is no sign that the surge tank overflow hose is wet, or has release any coolant below it, when slowly opening the surge tank cap, the relief hose blows steam There is no sign of coolant/water on the ground, no vapor out the exhaust, no water in the oil, no coolant leak inside the car from the heater core. The car always ran with the temp gause a hair above the mididle of the gauge, occasionally an up and down drift, which i attributed to the thermostat opening and closing. . My mechanic owns his own shop but was formerrly a Cadillac service tech for 15 years during the period from 82-97 he immediatly suspected head gaskets but a pressure test showed no leaks. Where can the water be going ? I checked the fan fuse and its ok, , Any way to check the temp switch ? I have been told it sometimes gives off a false signal., but in any event there is a loss of coolant.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The chances are 99:1 you have failing cylinder block head bolt hole threads = loss of clamping pressure = failing head gaskets.

The 1998 - 1999 Northstar was the worst series for head bolt thread problems. Cylinder leakdown (pressure) tests will not usually indicate problems - 100 psi is too low a pressure to force air/gas out past a failing fire ring - combustion pressures do the trick.
anatomy_of_a_headgasket.jpg


Before doing anything else - and DO NOT dump in some snake oil cooling system sealant - check the coolant purge line for constant flow and, if that's good, perform a cylinder block exhaust gas test. Rent the tester from a parts store. That will check for exhaust gas components in the air over the coolant in the surge tank - leaking head gaskets. Correct surge tank level is 1/2 to 2/3 full, cold.

Water crossover assembled.gif


Read the stickies on these problems in the Engines; Northstar forum. Stickies, marked with a push pin, are timeless necessary info.

Welcome to CF !!!
 

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White Diamond '03 DHS (with DTS floor shift)
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My mechanic owns his own shop but was formerrly a Cadillac service tech for 15 years during the period from 82-97 he immediatly suspected head gaskets but a pressure test showed no leaks.
A pressure test may not show a leaky HG. Remember, when you do a cooling system pressure test (assuming that is what he did), you are pressurizing the cooling system to only about 20 psi. That's good for locating an external leak, but the pressures in the cylinders when running can be 300 psi (at low loads) - 1500 psi. (at high loads), so a cooling system pressure test may not show a small breach in the HG. Follow Sub's advice and do a block test.
 

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1999 STS Diamond White - Single Family Ownership
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You need a reliable mechanic who knows Northstars to diagnose and avoid wasting money.
 

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Discussion Starter #5
My Mechanic has his own shop ( prior experience was 15 years at Nothshore Cadillac) He thought it was other issues like possible head gasket failure and engine burning off coolant, I felt that was not really possible, since engine does not really run rough, and there is no steam out the exhaust. A new pressure test at operating temp revealed a water pump leak. The pump was changed, gasket and thermostat, tightening of a leaky hose at the heater, and adding a couple coolant pellets. The car is running fine now, normal range on the temp gauge is a hair above the middle line, the car has about 160 miles on it since the fix and there is no loss of coolant. I guess I ducked a bullet.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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The use of the coolant sealant tablets during normal system maintenance was discontinued by GM/Cadillac in 2006. There is a specific Cadillac TSB that addresses this.

If you added a couple of tablets that's probably OK but don't add more. They tend to clog small coolant passages as well as the coolant purge line and its hollow bolt/nipple.

Make sure the purge line flows a small, steady stream to the surge tank. A clogged purge line causes oddball overheating events. Post #2
 

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1999 ESC
99' Eldo
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All good suggestions from knowledgeable Cadillac experts - but if you haven't found a solution - have your mechanic call Robert Hooper @ 805-440-3175 - he is owner of Thermaweld - THERMALWELD - LANDING PAGE - Head Gasket Repair | Thermalweld - he is the chemist who created the product 20 years ago - I flushed and added Thermalweld to my 1999 Eldorado last August - driven over 2500 miles with no loss of coolant - more importantly no more overheating - inserts are great and should last forever -if you want to invest $2500k+ or a new engine for about $5000+ BUT for $250 - I'm very happy keeping my '99 Eldo on the road
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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As always, be very careful when pouring magic potions into your cooling system ....... you may well render the entire engine and HVAC heating systems unfit for future overhaul, repair or maintenance.

ThermalWeld contains sodium silicate ("water glass") - the same stuff that was used to seize (destroy) engines during the ill-advised Cash For Clunkers programs about 11 years ago.

If you are of a mind, and need mental masturbation, read the linked website. You'll eventually get to the legal disclaimer that gets the "company" off the hook - "COOLING SYSTEM FAILURE - The original source of cooling system failure, if still present, must be identified and corrected before attempting a chemical repair -................ Underline mine.

Basically they're telling you to fix the problem before pouring in the snake oil.

Heads-up - and please learn WHY the earlier Northstars (especially 1997 - 1998 - 1999) suffered from failing cylinder block head bolt hole threads - not failing gaskets initially - pulled bolts which lead to failed head gaskets. A lot of the problem was cylinder block metallurgy and bolt thread size.

Scroll to the top of the page poll, click the lower right corner - view results - and see what our member have non-scientifically shown.

 

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2001 eldorado,2008 DTS,2005 XLR, '96 eldo,'95 eldo,' 89 eldo,'78 eldo,'11CTS-V
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This stuff cost $250?
I've got a bridge you might want to buy.
 
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