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a.dehlawi

2000 DHS Overheating with AC on and on idling speed

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Hi Everyone,

I've been reading posts in this forum since so many years and its been a great help :) but I couldn't find any answers to my problem.

I have a 2000 DHS with 98,000 miles on it. The car is in perfect shape and all the things work just fine except for this overheating problem that has appeared last month.

I drive it almost everyday and the temperature needle never went above the half mark but last month it started to overheat a bit (next mark after the half) with the AC on but it would go to normal when i start driving & also goes back to normal when i rev it upto 2500 rpm on idling. the needle does not moves if the AC is off. Now heres the mystery, This happens only every 1-2 days and sometimes stays normal for 3-4 days.

Everyone is saying that its the Head Gaskets. The reservoir tank was slightly leaking coolant near the cap so I replaced it but the car started overheating too much after replacing it. I thought that an air pocket is causing this so I thought of bleeding it today (engine off> disconnected the 3/8" hose> blocked both overflow hose & 3/8" hose from the reservoir tank> pumped through the reservoir tank) there was too much air that came out and finally the coolant started to come out but the coolant stopped once I started the engine (with the cap on but still blocking the 2 hoses) the fans kicked in but the needle jumped upto the next mark after the half it came back to normal when I raised the revs upto 3000 but after sometime it went back & this time it dint came back to normal. one more thing, the rev has started to stay at 1500 & only comes down when i switch on the AC.

Now does anyone has idea what could be the problem?? I think the water pump is not functioning properly but how can I test it? why the 3/8" hose stopped pouring coolant when I started the engine?? Could it be the water pump tensioner??

Following are some tests and replacements I have done so far:

1. Checked and both fans are working fine at high and low speeds.

2. Replaced the thermostat & cleaned the radiator.

3. Replaced the reservoir tank and the cap.

4. Got the water pump checked, The mechanic says it works fine but i doubt it.

NOTE: The needle never went beyond the first mark after the Middle/Half mark...NEVER

I really need to fix this but I really dont think that the Head Gaskets are blown, It would be very helpful if any of you could share your experience with me.

Thanks,

Dehlawi

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Does the system hold pressure?

Is the coolant concentration 50% coolant to 50% water?

Have you checked to see if the purge line is clogged? If it is, the system will not let air out, you will not be able to get enough coolant in, and the water pump will cavitate and not pump efficiently. CHECK THE PURGE LINE AND DO NOT BLOW INTO IT TO CLEAR IT

There is a hose on top of the tank, not the over flow the other one, with the engine cool gently pull it off and let it hang so that coolant does not get on the paint

start and let the engine idle

Go look at the hose, it should flow coolant steadily if not your air purge line is clogged, do the test and come back and let us know the result of the test


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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WHAT YOU DID WAS WRONG!!!!!!!! DO NOT BLOW THROUGH THE TANK OR PURGE LINE, YOU MAY HAVE CLEARED IT NOW, AND YOU WILL NEED TO LET IT CLOG AGAIN

DO THE TEST I DETAILED ABOVE AND REPORT BACK


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Waterpumps do NOT go bad unless they leak. But check the water pump belt and tensioner to make sure the tensioner is applying enough pressure

What was the result of the pressure test on the cooling system? Have it pressure tested does it hold pressure?


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I did as the mechanic asked me to do, Ok now how do I check if its holding the pressure? i thought the purge line should be clear ? why do i have to let it clog? ok i will do as you said and will report back tomorrow.

Thanks

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If it¨s cloged the dirt will just go back a bit when You blow and then return as You run the engine......

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You check if it is holding pressure with a pressure tester. Connect it to the surge tank, pump it up to 18 psi and let it set overnight. If the pressure goes down, you have a leak, but this IS NOT a test for HG's. You need a block test kit to test the air in the surge tank for exhaust gases if you suspect a HG.

The purge line SHOULD be clear (of obstructions) and flow coolant.

why the 3/8" hose stopped pouring coolant when I started the engine?? Could it be the water pump tensioner??

Check the tensioner. If it is tight, the pump is turning. If the pump is turning and nothing is coming out, then it is obstructed or has air (or exhaust gases) in it (thus no coolant flow).

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I did as the mechanic asked me to do, Ok now how do I check if its holding the pressure? i thought the purge line should be clear ? why do i have to let it clog? ok i will do as you said and will report back tomorrow.

Thanks

Please stop reading into what I am writing, I didnt say anything about pressure or color, its FLOW. The diagnostic is to see if it FLOWS...WITHOUT disrupting it FIRST

BECAUSE you BLEW INTO the PURGE LINE YOU MAY HAVE DISLODGED and I SAY MAY HAVE DISLODGED the clog. IF you do the test AFTER DISLODGING the clog it will APPEAR to be clear ONLY to CLOG AGAIN LATER.

DO YOU UNDERSTAND?? ITS NOT PRESSURE, it MUST FLOW, and you MUST NOT BLOW IT CLEAR

Again, this is what you need to do

1) with engine cool

2) pull the purge line off the top of the tank and let it hang

3) start and idle engine,

4) check the purge line, it should flow a steady stream of coolant

If it does, keep in mind that you MAY have cleared it by blowing, but that is ONLY temporary, and it MAY clog again. THE ONLY way to clear it is to remove "the bolt with a hole in it" and clean it out, I have SEEN a 2 inch long piece of silicone sealer stuck in one!

Let us know how this turns out WE ARE TRYING TO SAVE YOUR ENGINE HERE


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thank you Ranger & BodybyFisher for the deatils, Heres what I did today:

Took the car to this radiator shop and he checked the radiator flow, there was too much dirt and rust in the hoses and he cleaned it all up.

the flow was good though, now we kept the car started with AC on for about 1 hour and the temp needle stayed on the 12 o'clock mark.

Then i drove it back home (about 6 kms) it moved to the next mark a lil bit at the traffic light but then came back to normal in a min.

Now I went out after 4 hours and it was normal for about 40 mins and then the needle started to move to the next mark after the middle, I turned off the AC and then the needle started to move from 12 o'clock to the next mark & then back to normal even while driving (40-60 mph) and it kept on doing this..

I live in Saudi and it is very very hard to find qualified technicians here :( I will look for this pressure tester & will do it for sure.

Now is there any way to check if the Head Gaskets are gone? I need to be sure before spending $2000 on this job.

one more thing, The Radiator shop guy did not add coolant to it and said to wait for a day or 2 to make sure if it performs well. (I KNOW I SHOULDNT HAVE LISTENED TO HIM AND SHOULD HAVE ADDED THE COOLOANT)

Will check the tensioner on Saturday and report back.

Thank you all so very much

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One More Question...

Shouldn't it be overheating too much if the Head Gaskets were gone?? the needle never goes above the 12 and a half mark or 1 o'clock mark max.

Thanks for all your support and help :)

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Now is there any way to check if the Head Gaskets are gone?

Yes, get a block test kit that tests the air in the surge tank for the presence of exhaust gases. Do it after and overheat situation, but DO NOT add coolant before the test. http://www.arrowheadradiator.com/head_gasket_or_combustion_leak_test.htm

Shouldn't it be overheating too much if the Head Gaskets were gone?? the needle never goes above the 12 and a half mark or 1 o'clock mark max.

When a HG fails, it is usually a slow process. It starts out as minor overheating and slowly progresses to coolant loss, worse overheating and eventually (could take a year) to undriveable.

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Thank you Ranger,

I will look for this block test kit here. I also found a leak on and replaced the left plastic side wall of the radiator, now the radiator shop guy checked the thermostat and said that the one i have will only open at higher temperatures and that was the cause of this overheating & I should buy the one that would open at lower temperatures in order to keep the car's temp normal. I'm trying to find such thermostat but couldn't till now (any suggestions? part # etc?)

Now the car doesn't has a thermostat and the temp has been very much better than before i.e the needle moves to the next mark but comes back to normal within 5-7 mins and this happens with AC on as well as with the AC off and at idle :)

I think this is happening because the fans wont start at the right temperature because the temp sensor is not getting the right signals.

Could it be the thermostat? I'm very happy to drive the car around because its not "overheating" like before :')

I'll still check the waterpump tensioner tomorrow and any suggestions on the thermostat part # or any details would be really appreciated.

Thanks

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A bad thermostat will bind an cause overheating, the first thing to do when you overheat is to check the coolant level, then the purge line then the thermostat


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I think the factory thermostat starts to open at about 188 degrees if I remember correctly. Fans come on at 224 degrees (without A/C). They are always on with the A/C. Thermostat part #12559807

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Thanks Ranger,

Shall i go for a lower temperature thermostat? like 160 degrees?

I had a GTO and I replaced the thermostat with HyperTech low temperature one... It really made big difference there.

Now the tensioner was fine but i still replaced it (just to make sure). The only thing left now is the thermostat.

Will report tonight.

Thanks

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No just put in the stock thermostat, its not degrees, its whether or not its opening, and dont use an aftermarket stat


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks Ranger,

Shall i go for a lower temperature thermostat? like 160 degrees?

I had a GTO and I replaced the thermostat with HyperTech low temperature one... It really made big difference there.

Now the tensioner was fine but i still replaced it (just to make sure). The only thing left now is the thermostat.

Will report tonight.

Thanks

I'm with BBF. Stick with the factory thermostat.

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