Supermutt Posted July 31, 2023 Share Posted July 31, 2023 I am trying to find out what the radiator full level is on my 1996 DM686S ? I topped it off pretty much to the bottom of the filled neck and it’s puking it out the cap vent line. No expansion tank on this truck. I have no water in oil, no oil in coolant, no air bubbles in radiator and also used block test and it did not turn yellow. Sooooo Did I just overfill it or ? thanks Quote Link to comment Share on other sites More sharing options...
D-Day Posted July 31, 2023 Share Posted July 31, 2023 The radiator cap needs to be replaced every couple of years and that should help with that problem 1 Quote Link to comment Share on other sites More sharing options...
Supermutt Posted July 31, 2023 Author Share Posted July 31, 2023 Thank you, I honestly think it may be the original lol. Do you know if it should be full to the filler neck or an 1” or so below. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted July 31, 2023 Share Posted July 31, 2023 Most trucks of that vintage had a "de-airation" tank on the top of the radiator. The tank you fill doesn't empty directly on to the tubes of the radiator. The top tank most often drains into the suction side of the waterpump. There is a small hole or line, the vents any air in the engine or on top of the radiator tubes into the de-airation tank. A very small amount of coolant is allowed to circulate right back to the waterpump. The idea is to get all the air out of the coolant circulating within the engine and radiator. The de airation tank is also an expansion tank. There are many kinds of necks and some will not allow it to fill the tank all the way to the top so it will not puke out, other like my Marmon you can fill all the way up and it will puke a little out if you don't stop with the coolant down a little from the top. I don't know how yours is set up. Quote Link to comment Share on other sites More sharing options...
D-Day Posted July 31, 2023 Share Posted July 31, 2023 Like all older equipment within an inch of the filler neck is considered full always depends on the depth of the top tank 1 Quote Link to comment Share on other sites More sharing options...
Supermutt Posted July 31, 2023 Author Share Posted July 31, 2023 Mine seems like a standard tank. Regular 10lb cap with a relief in the filler neck with the factory line routed down the side to just below the frame. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted July 31, 2023 Share Posted July 31, 2023 Shine a light in and see if you see radiator tubes, I'd be shocked if you could. My early 80's vintage stuff all had a divided top tank, the cap is on the de airation section. Also 10 PSI sound high, most I think were 4 or7 psi, but I am used to older stuff. Quote Link to comment Share on other sites More sharing options...
Supermutt Posted July 31, 2023 Author Share Posted July 31, 2023 The book does spec a 10 lb cap. From the bottom of the filler neck to bottoming out is about 2.5”. I have attached a pic. Also there is what looks like a low coolant sensor on the tank. I can remember the type of tank you are talking about. Pretty sure back in the day my e9 500 had that. 1st generation. Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted July 31, 2023 Share Posted July 31, 2023 That is very similar to my Marmon top tank. You'll notice it is much bigger than the top of the "core", and if you look down through the filler, you'll not see the rad tubes. It is an integral de airation tank. It still can push coolant out, if overfilled. As long as it doesn't continue to force stuff out every time you run it, I wouldn't worry. I've got a few top tanks not mounted to cores, I'll see if I can get a picture to show how they work. The idea is to keep all air bubbles from mixing in the coolant and bursting on the hot metal inside the engine. By keeping the "reserve tank" on the top of the radiator and out of the main circulating coolant, the air that is in the system makes its way to that tank, keeping the main flow air free. Older radiators the cap looked right down on the top of the radiator tubes, the main flow of coolant was exposed to the air at the top of the tank and high flow would tumble and pick up some air and bring it into the engine. 1 1 Quote Link to comment Share on other sites More sharing options...
Geoff Weeks Posted July 31, 2023 Share Posted July 31, 2023 (edited) Here are some pictures of a top tank off a core 1st pic is the top tank as it sits ontop of the rad 2nd is of a bleed hole between the top of the core to the expansion tank 3rd is a pic of the tank where it bolts onto the core, you'll note the upper hose connection passes thru the expansion tank to the upper core area. Most all of the coolant passes down through the core, but any air can pass out the little bleed hole (a very minor amount of coolant does also) the last picture is the 1" or so line that goes to the inlet side of the water pump, any coolant you add to the expansion tank enters the engine from this line. Any coolant that passes from the bleed hole returns to the block this way also. On the Big Cam engine this rad was hooked too also had a bleed from the top of the water cooled aftercooler and the engine upper waterrail. as well as one more 1/4" NPT port for a low coolant sensor. Edited July 31, 2023 by Geoff Weeks 1 Quote Link to comment Share on other sites More sharing options...
Vladislav Posted July 31, 2023 Share Posted July 31, 2023 Interesting, thanks for the info shared. I haven't put my nose into 80's years' Mack radiator so far. Was going to but could stop myself from one more deal having many others unfinished. My R-model which I drive from time to time (about once in two years recently) has that same sensor in the upper tank and red lamp on the dash lights on with a mark "shut off the engine" below it. The previouse owner told that's because of low coolant level. And I still haven't add any and even looked into during already 11 years I own the truck. The temp gauge readings are Ok though. Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment Share on other sites More sharing options...
Geoff Weeks Posted July 31, 2023 Share Posted July 31, 2023 That tank was off a 1983 IHC cabover. Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted August 1, 2023 Share Posted August 1, 2023 that style top tank with low level sensor will find it's proper level. long as it's NOT constantly puking coolant ;; coolant at bottom of filler neck IS TOOOO MUCH. need room for expansion. all above info is also correct . 1 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted August 1, 2023 Share Posted August 1, 2023 21 hours ago, Supermutt said: The book does spec a 10 lb cap. From the bottom of the filler neck to bottoming out is about 2.5”. I have attached a pic. Also there is what looks like a low coolant sensor on the tank. I can remember the type of tank you are talking about. Pretty sure back in the day my e9 500 had that. 1st generation. water filter looks to have been on there for a while (rusted); coolant been changed recently ?? 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted August 1, 2023 Share Posted August 1, 2023 23 hours ago, Supermutt said: I am trying to find out what the radiator full level is on my 1996 DM686S ? I topped it off pretty much to the bottom of the filled neck and it’s puking it out the cap vent line. No expansion tank on this truck. I have no water in oil, no oil in coolant, no air bubbles in radiator and also used block test and it did not turn yellow. Sooooo Did I just overfill it or ? thanks yes; i'd say so , reason for topping it off in first place ??? doing a super service or was it low and indicator light on dash lit up ??? 1 Quote Link to comment Share on other sites More sharing options...
mowerman Posted August 1, 2023 Share Posted August 1, 2023 I am thinking that radiator cap will do the trick that radiator. Looks like the one in my 66. 1 Quote Link to comment Share on other sites More sharing options...
Supermutt Posted August 1, 2023 Author Share Posted August 1, 2023 Coolant filter & coolant is going to get changed out. Quote Link to comment Share on other sites More sharing options...
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