Low coolant - neg pressure test

[bl78ljb]

I just purchased a 1998 Suburban 2500, and had the low coolant light go on, and so I had the cooling system flushed and pressure tested. When this was done I was told that it passed the pressure test and had no leaks detected at all. However, a few days (and about 200 miles) later the low coolant light came on with the truck cold and then went off when it warmed up. I have yet to add fluid again to see if this goes away but as I am more familiar with gasoline engines I was wondering if there is anything else I need to look into. I don't want to get into extensive diagnostics if I don't need to as it is only 5 F here in Maine with a 20 mph wind.

Also, if there is anyone from this area I was wondering about a competent diesel shop in the area.

Thanks
Bryan
Bangor, ME

[gmctd]

Welcome to the forum, Bryan..........

Check the level in the coolant reservoir tank - could be they neglected to let the system equalize.

Fill it if it is low, then check again tomorrow.

While you're there, look at the upper heater pipe, where it connects to the t-stat crossover - that fitting is problematic, even without radiator service

[sailun]

Bryan,

My 97 has been doing the same thing, randomly, every winter, ever since I bot her in 2001.

I add a splash of antifreeze, once a year, and it stops doing it. By a splash I mean less than a cup.

I would only get concerned if you need to add AF on a regular basis.

[baker2acre]

I agree GMCTD....

bl78ljb... Check your reservoir tank 1st! It should be on the passanger side fire wall. There is a sensor about half way down and if the coolant is below that sensor, light comes on. When your engine is cold the coolant will actually constrict abit and over the long distance of your cooling system that could amount to a couple inches in you reservoir. To the opposite, when warm it will expand and fill the tank (light off.) This is why it is also refered to as an "expansion" tank. Fill it (cold) to the line on the side that says "full" and check it again and again until your confident you do not have any coolant loss. A quicker way is to place a piece of cardboard below the engine compartment. (If you don't have a garage make sure to weigh it down for your 20mph nights!!) In the morning, you'll easily be able to spot some "drips" and most importantly be able to distinguish between "black oil- red tranny fluid- and yellowy green coolant." A bonus is that without moving the cardboard you can "trace up" to the general area of the engine where the leak may be from. Oh, and if you happen to not have any black, red or yellow dots.... panic!! :eek: You may not have anything in your engine at all!! I'm only half way kidding. :p In all honesty, little drips are common with the age on our trucks and some of the OEM fittings are just another way to spell leak. Yours may have these replaced already and may not have any leaks. But it never hurts to check the oil and trans fluid while you're there!! :D Welcome, good luck and keep us posted!!

[sailun]

Baker just reminded me about the expansion.........


So plug 'er in at night, and you won't get the light !

(Unless there really is a loss of fluid somewhere)

[65TD]

Probably flushed and filled it when it was warmer.

Fill it to 'Full Cold' mark on the coldest day and your good to go.