I have an 03 4.0 with 148k on her. It just sprung a substantial coolant leak yesterday. I have had to add between a pint and a quart of coolant every oil change for quite a while but noticed a large puddle on the ground yesterday and was a gallon and a half low. I saw no signs of a leak on the radiator, hoses, t-stat, or water pump. I pulled the air intake tube, throttle body, fan and shroud for a closer look and found a puddle of coolant on top of the engine in the valley. I could not locate an exact source. Are there any common causes for this? My dad has an 02 2.3 that had a cracked intake manifold but I haven't been able to find many threads about SOHC 4.0s intake leaking. Maybe I'm bad at searching? Any insight is appreciated.

 

Head gasket ok?

 

I dunno I guess its possible a head gasket could be leaking so fast but in my previous experience with my 06 f250 6.0 psd there was only evidence of coolant residue around the gasket where the head met the block. It was just seeping. As soon as I filled the mazda up with coolant and started it there was a puddle collecting on the ground from the overflowing puddle on top of the engine. I will definantly take a closer look at the heads tho. Thanks.

 

Is the head straight? If youve got a motor that overheated, the head might be warped out of shape, thus making the gasket useless

 

Did you take a look at the lower thermostat housing? I have a small leak, similar to yours. I am pretty sure the lower thermostat housing is either not sealing at the bottom near the back or has a small crack in it.

I plan to order a new housing and seal and install it in hopes that it solves the problem.

I have 168K miles on mine.

 

Ianyboy the temperature has only spiked once since I've owned the truck due to a sticky tstat but it quickly went back down. I guess it is possible that it did get very hot a couple days ago it could have been low on coolant to register. In2 fx4, I did read something about the lower thermostat housing being prone to cracking. I will continue to tear it down and see what I can see. I'm in the middle of a 60 day turnaround at work so won't have a lot of time to work on it but I will work on it a little every day and report back if I find anything. Thanks for the help guys.

 

Thanks for the posts on V6~4.0L~SOHC engines & TStat housings; good reference info.
Replaced the old leaking FRPlastic TStat Housing with a new Aluminum TStat Housing
in 2019Aug on a 2001 Ford ExSportTrac; no leaks as of 2020Mar after ~5K more miles.
My full write up with pics on that repair:
http://2001fordexplorersporttrac.fandom.com/Coolant_ThermoStat_Housing