Jimmy825 Posted February 3, 2021 Share Posted February 3, 2021 I have a 97 RD688s with an E7 350. When driving along when cold outside, my temperature gauge does not go up very much and if I idle, the heat I get goes cold. If I put a piece of cardboard in front of the radiator, it gets warmer and on a hard pull, it will get up to 180 to 200 and then level out after the pull back to around 130 to 140. But if I idle, it blows cold. I bought a winter front recently and will try that but I was wondering if it may have a stuck open thermostat. Or does a Mack just run cold all the time. I have never experienced a truck having an issue like this Quote Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/ Share on other sites More sharing options...
Rob Posted February 3, 2021 Share Posted February 3, 2021 Cooling system restriction, water pump weak, thermostat not modulating, are all good indications of the symptoms you mention. If you hold a high idle speed and the heater increases it's discharge temperature, there is not enough coolant flowing through the core at low engine speed is the long and short of it which very often is a weak water pump, or restricted cooling system. Same thing with the engine cooling as the coolant is dwelling in the radiator too long removing heat before it's circulated back through the system. On my own trucks I'd drain the cooling system down, remove the thermostats, refill with a mixture of clean water and a commercially available cooling system flush in the correct ratio for the system, and allow it to operate per the instructions. Then flush with clear water, reinstall new thermostat(s), and refill with a 50/50 mix of anti freeze/distilled water combination. Certainly wouldn't be a bad idea to replace the water pump at this time, but most won't if it's not leaking. I've seen several water pump impellers eaten away or noticeably compromised on engines over the years although not leaking so not a bad idea to replace with a high mileage, or aged engine. Just my thoughts. 1 Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468194 Share on other sites More sharing options...
Vmac3 Posted February 4, 2021 Share Posted February 4, 2021 You would be correct with the things you have mentioned. Coolant will degrade over the years and will require to be serviced (flushed and refilled with new coolant). Sometimes its a case of out of sight out of mind. If the coolant does not have the right protection against cavitation and corrosion, then damage will occur. I have seen vocational trucks with mud in the cooling system. This causes a disaster in the heater core and radiator. You can get test strips to check the antifreeze condition at your parts store. V 1 Quote Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468238 Share on other sites More sharing options...
OldRedMack Posted February 5, 2021 Share Posted February 5, 2021 I would start with the thermostat. Quote Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468362 Share on other sites More sharing options...
MACKS Posted February 6, 2021 Share Posted February 6, 2021 Every truck I owned lost its heat after idling a while in cold temps but you should reach operating temp when driving empty or loaded.. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468377 Share on other sites More sharing options...
fjh Posted February 9, 2021 Share Posted February 9, 2021 The down side to changing the coolant now is you, will defiantly find the week spots! 1 Quote Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468621 Share on other sites More sharing options...
Vmac3 Posted February 9, 2021 Share Posted February 9, 2021 15 hours ago, fjh said: The down side to changing the coolant now is you, will defiantly find the week spots! so true Quote Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468655 Share on other sites More sharing options...
theakerstwo Posted February 9, 2021 Share Posted February 9, 2021 Also if the fan is running at idle it cools the engine in two ways.One is it cools the coolant and another way is it blowing cold air across the outside of the engine. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/65762-loss-of-heat-when-idling/#findComment-468670 Share on other sites More sharing options...
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