: 98 Eldo N* 4.6 Overheating



MtlSphere
04-03-05, 02:26 PM
I bought a 98 Eldo in December. The car seemed to be in great shape. Now thinking...LEMON!

There was a crack in the plastic tanks of the radiator when I bought it. After replacing the radiator all was fine until about two weeks ago. The temp guage indicated the engine temp becoming unstable. Checked coolant level and it was fine. I noticed engine temps climbing and falling but never below normal. Then while running errands on a cool day it overheated. I replaced the thermostat and flushed the sysytem but the condition persists. It continues to overheat! I replaced the W/P belt and the pump is turning so what's the problem here?

Mtl:banghead:

growe3
04-03-05, 04:06 PM
How many miles on the car?
You note that you flushed the system, what did you use?
Check the tensioners for the water pump belt. Sometimes the tensioners will stick and not apply full pressure to the belt, and the water pump will slip at higher RPM’s.

These engines need to have sealant in the coolant system, the flushing agent may have removed it and started an internal leak, i.e., a head gasket leak.

On a cold engine remove the lower radiator hose where it attaches to the water pump. Pour two (2) tubes of Bars Leak Golden Seal into the radiator hose. The factory used this product originally.

Do not add this sealant to the surge tank, only to the radiator hose as described. If you put it in the surge tank it will not circulate and do its work. It may in fact cause some blockage, if placed in the surge tank.

Before topping off the coolant, check the hollow bolt (see attached image). Remove the small 3/8" hose and coolant should flow out. If not, use a drill (matching the hole size) and twist by hand, to be sure bolt is clear of any buildup.

With the surge cap off, use air pressure to blow through the small hose. You should hear the air clearly at the surge tank. It is necessary for this part of the system to be clear, so that the water pump can vent air to the surge tank.

Refill with a 50/50 mix of coolant. Leave cap off. With the engine at about 180-190 degrees, the coolant level in the surge tank should be about 2” below the neck ring.

Replace cap and drive easy for a while to let the sealant try to do its job.

-George

MtlSphere
04-04-05, 01:23 AM
Thanks for the reply!

There are 94k miles on the car. I flushed the system with water under pressure. I prefer to avoid caustics and solvents when flushing. I have found over the years this has been adequate to remove remaining coolant, sediment and scale. All in all the engine was quite clean and flow seemed unobstructed. I replaced the w/p belt and excersized the tensioner at that time. While the old belt was worn there appeared no obvious signs of slippage. I poured the BarsLeak in the upper hose.

After my post I decided to apply the "shotgun" approach. Considering the mileage I decided to replace the waterpump, and thermostat (again). It seemed while looking at the engine compartment that replacing the waterpump should be quite easy and relatively quick. The key is to have the special w/p tool on hand and I did. The only issue to speak off was the notched tab on the pump. The shop manual says to locate this tab in the 7 o'clock postion upon installation. I was already recycling curse words before I found that the notched tab actually belongs in the two o'clock position. After that adjustment re-installation was quick. Here I must mention that I removed the thermostat housing, thermostat, and neck as a unit for inspection. Scrutiny from the engine side of the assymbley revealed the the lower part of the thermostat was sticking in the bore of the housing. The bore appeared clean and free of any build up however a test fitting of the new replacement thermostat did not have the same interference but I wire brushed the bore vigorously none the less and finished the install. I added one tube of barsleak (again to the upper hose) and refilled with coolant (through the upper hose) until it started to dribble from the thermostat housing. I replaced the hose, topped up the surge tank and started the engine. All is well. The engine came up to what had been "normal" on the guage and stayed there. I took the little woman to dinner and then we went for a spirited drive on the hiway. The temp remained stable throughout. I did not know about the hollow bolt. Good info that! I will check and clean that tomorrow. Thanks again for the reply!

Just curious why my post was moved? It seemed many technical questions were posted there.

growe3
04-04-05, 07:57 AM
Well it sounds like your have done a thorough and careful job. I hope it solves your overheating problem. Regarding flushing; I would not flush the system, just drain as much as possible. Flushing with water makes it a little harder to get the correct 50/50 mix back into the system.

Do check the hollow bolt and the hose back to the surge tank when you can, it is important for them to be clear.

As to why your post was moved, probably because it is more of an engine question, rather than just a Seville or El Dorado question.

-George

MtlSphere
04-08-05, 11:47 PM
George,

Thanks again for the reply!

I drove the car for a few days after my last post and all seemed fine. No, I didn't check the hollow bolt. Musta been a big mistake!

Since the temp was stable I thought the hollow bolt issue moot. Then I took the little woman to dinner last night after work. I was confident my temp troubles were behind me so I chose a nice restaurant on the other side of town. All during the drive, mostly highway, I was really keeping an eye on the temp guage. Stable, no troubles...until we were about to turn into the parking lot of the restaurant when I glanced down again and it was in the red. No bells or whistles yet but they weren't far off. By the time we parked it was in camel mode and steam was wafting from under the hood...and brother I was pissed!!

We were more than twenty miles from home. Nothing to do but go inside and have a meal. We took our time and by the time we returned to the car it was cool. I explained the camel mode to my wife and boasted, as much to reassure myself, of a Motor Trend article I had read about the N* and how the editors of the magazine had completely drained the coolant and took the car on a road trip and how at the end of the trip they refilled the coolant and all was well with the car. So we fired that hummer up and pulled out into traffic. It wasn't long before the bells and whistles were demanding my attention and I could have sworn the DIC used some rather choice expletives about idleing and shutting down the engine. But I was just as pissed at it was so I kept going. I swear I could actually feel the ECM switching cylinders and while power was down, idle was rough, I was able to maintain traffic speeds with little effort all the way home.

This evening I took it apart again not really knowing what to expect. I checked for sticking thermostat and found it to be in good order. I placed it in a pan and heated the water and it began to open at 179*. It was fully open at 192*. Seemed well within spec. While replacing the thermostat I broke a housing bolt with my air ratchet and had to go to the store for a replacement. Then turned the pressure down on the compressor. That's when I came upon the hollow bolt. I stuck a piece of coat hanger wire into the end and it didn't go in very far. So, I removed the bolt and found it to be completely clogged. The coat hanger wouldn't clear it so I turned to Mr. Dremel and his 10k RPM. That made quick work of the clog. I reinstalled the bolt and hose. I flushed the system as before. Put in the Barsleak, fresh coolant and topped up the radiator via the upper hose then the engine via the surge tank then fired her up. Oh, I cleared the codes with my code reader just prior. I just got back from the test drive and once again all seems normal.

My question...could that blocked hollow bolt have caused all of this? Enough pressure in the system to keep the thermostat from opening? There is a wobble valve in the thermostat; shouldn't that haveequalized the pressure? And if this doesn't fix it how much lighter fluid does it take to toast an Eldorado?

Mtl

NolieJames
04-09-05, 01:43 AM
Don't toast the Eldo!! If you're gonna do that, I'll adopt it. :sneaky:

I've got similar issues with my beautiful '96 DeVille. A GM dealership told me they pressure tested it, and the head gaskets were shot, but I didn't wanna pay what they wanted to do the job. I brought it back home and decided to pressure test it myself. Lo and Behold, I pumped it up to 20 lbs. and it stayed there for an hour and a half. Looked good to me! So I replaced the waterpump and cleaned out the surge tank. Once the thermostat gets in tomorrow, we'll see how she does. Thanks for the tip on the hollow bolt Growe3, I never would have thought of that! :hmm:

MtlSphere
04-09-05, 04:11 AM
What a great forum this!

And I thought the boys over at Corvetteforum.com were good!

Did a whole lot more reading/research...note the time and wee hour of this post.

I've been reading up on the coolant system of the N*. Man I thought my Vette had cooling issues! Anyways found a great couple of articles about the cooling system; the most interesting concerning water pump vapor lock and the reverse flow thermostat. So it seems that a clogged hollow bolt can cause vapor lock and subsequent loss of coolant flow. And considering I have replaced and serviced ALL parts of the cooling system if this doesn't fix it adoption is not an option...I'm watchin' it burn!!!! LOL and goodnight!

growe3
04-09-05, 11:14 AM
George,

Thanks again for the reply!

I drove the car for a few days after my last post and all seemed fine. No, I didn't check the hollow bolt. Musta been a big mistake!

Since the temp was stable I thought the hollow bolt issue moot. Then I took the little woman to dinner last night after work. I was confident my temp troubles were behind me so I chose a nice restaurant on the other side of town. All during the drive, mostly highway, I was really keeping an eye on the temp guage. Stable, no troubles...until we were about to turn into the parking lot of the restaurant when I glanced down again and it was in the red. No bells or whistles yet but they weren't far off. By the time we parked it was in camel mode and steam was wafting from under the hood...and brother I was pissed!!

We were more than twenty miles from home. Nothing to do but go inside and have a meal. We took our time and by the time we returned to the car it was cool. I explained the camel mode to my wife and boasted, as much to reassure myself, of a Motor Trend article I had read about the N* and how the editors of the magazine had completely drained the coolant and took the car on a road trip and how at the end of the trip they refilled the coolant and all was well with the car. So we fired that hummer up and pulled out into traffic. It wasn't long before the bells and whistles were demanding my attention and I could have sworn the DIC used some rather choice expletives about idleing and shutting down the engine. But I was just as pissed at it was so I kept going. I swear I could actually feel the ECM switching cylinders and while power was down, idle was rough, I was able to maintain traffic speeds with little effort all the way home.

This evening I took it apart again not really knowing what to expect. I checked for sticking thermostat and found it to be in good order. I placed it in a pan and heated the water and it began to open at 179*. It was fully open at 192*. Seemed well within spec. While replacing the thermostat I broke a housing bolt with my air ratchet and had to go to the store for a replacement. Then turned the pressure down on the compressor. That's when I came upon the hollow bolt. I stuck a piece of coat hanger wire into the end and it didn't go in very far. So, I removed the bolt and found it to be completely clogged. The coat hanger wouldn't clear it so I turned to Mr. Dremel and his 10k RPM. That made quick work of the clog. I reinstalled the bolt and hose. I flushed the system as before. Put in the Barsleak, fresh coolant and topped up the radiator via the upper hose then the engine via the surge tank then fired her up. Oh, I cleared the codes with my code reader just prior. I just got back from the test drive and once again all seems normal.

My question...could that blocked hollow bolt have caused all of this? Enough pressure in the system to keep the thermostat from opening? There is a wobble valve in the thermostat; shouldn't that haveequalized the pressure? And if this doesn't fix it how much lighter fluid does it take to toast an Eldorado?

Mtl

Short answer is yes, the hollow bolt being clogged could have caused the problem. The water pump needs to vent air bubbles away or the pump can cavitate. Damaging the pump and also not moving enough coolant.

One thing that you did not mention, did you clear the small hose that leads back to the surge tank? With the bolt being blocked, as you noted, I would expect partial blockage in the small hose also.

Remove the surge tank cap and cover with a rag or two.
Remove the small hose from the hollow bolt and blow several bursts of compressed air thru the hose.
Reconnect the hose and the surge tank cap.

-George

MtlSphere
04-12-05, 12:23 PM
Hey George,

It's been four days and all is well. Yes, I did use air on the hose and it did not seem to be blocked as it blew the rag off the surge tank immediately. Sunday I got onto the loop around the city to put it through it's paces and the guage read steady throughout.

I did some research on the guages and have found that the 98 model year was the last year for "actual representative" guages on many GM vehicles. In subsequent years guage readings are dependent on a ECM algorithym. Either it's normal or it's not. The ECM sees the actual flucuations from the sensors then decides if it's within parameters or not. If it is then you see a normal indication, if it's not then the ECM indicates an "out of range" / HOT or cold reading. I'm not in favor of this sort of engine management.

I'm on vacation this week and the lil woman has been driving my car to work. Time to get the Vette ready for summer.

Thanks again for all your good input!

STS 310
04-12-05, 05:47 PM
MAybe a temp reading on your DIC would be a better indication of actual temp than the guage. I know its possible on pre 98 models and I am pretty sure it can be added to your current Info on the DIC through the PCM.