Soft Spot in Floor, Can't Find Leak!!!

[heit97]

I have a 2016 T24FQ MX toy hauler. See the image of the layout. There is a large soft spot in the floor on the drivers side of the front bed, and a small soft spot on the passenger side. I've checked everything I can possibly think of, and had it in two shops. Nobody can figure out what's going on. Here's the sequence of events to this point.

Mar, 2018 - Purchased used. There were no signs of damage. It's possible I didn't notice it, but not likely.

Aug, 2018 - Was on a camping trip and noticed the soft spot in the floor on the drivers side.

Aug, 2018 - I checked all plumbing and seals. No sign of leaks or damage.

Sept, 2018 - Took it into a shop to investigate. The shop check all plumbing and seals. Could not locate the leak. The shop cut open the underbelly and dried out the floor from underneath. The conclusion from the shop was the leak occurred and was fixed before I purchased the trailer.

Note: The soft spot didn't seem to get any worse for the rest of the 2018 season.

Nov, 2018 - Winterized and stored until Apr, 2019. It was store in my driveway without a cover to verify the shops conclusion that the leak was fixed. There was a fair amount of snow and ice on it throughout the winter.

Apr, 2019 - De-winterized. Soft spot what noticeably worse. I cut open the underbelly and found the floor and insulation were wet. The invalidated the shops conclusion.

May, 2019 - Checked all plumbing and seals. No sign of leaks or damage. Sprayed trailer down thoroughly. No signs if water in the underbelly.

Summer, 2019 - Use 6 time checking the underbelly each time. No signs of water.

Aug, 2019 - Noticed a small soft spot on the passenger side of the trailer.

Sept, 2019 - Took to another shop. They checked all plumbing and seals. No sign of leaks or damage. They also did a Seal Tech test. No signs of leaking.

Currently - The floor is still dry.

A few more notes. I've only hauled it in the rain once for about 10 minutes. I live in Utah so it's pretty dry in the summers. I have never seen water or signs of damage on the inside of the trailer. The water seems to be getting to the subfloor from the outside somewhere.

I'm out of ideas. I'm ready to unload this thing for pennies to get it out of my hair. If anyone has any ideas of where this water could be coming from, or how to figure it out, I would greatly appreciate it.

[RV_daytrader]

You posted: Nov, 2018 - Winterized and stored until Apr, 2019. It was store in my driveway without a cover to verify the shops conclusion that the leak was fixed. There was a fair amount of snow and ice on it throughout the winter.

Apr, 2019 - De-winterized. Soft spot what noticeably worse. I cut open the underbelly and found the floor and insulation were wet. The invalidated the shops conclusion.

Since it leaked over the winter when it was winterized it is NOT a plumbing leak. Has to be a roof or window leak IMO.

[Chum_lee]

I notice that the soft spots in the floor are on opposite sides of the RV and beneath the edges of the windows. Coincidence? Does this seem to happen when the RV sits, or when you use it? Or both? If it happens when sitting I would suspect an exterior water source, most likely, the windows. If it happens when you use it, I would suspect plumbing.

IMO, You have a SUBSTANTIAL leak to get the floor that wet judging from the discolored sub-floor and the extent of the soft spots.

Have you tried using an infra red thermal gun looking for hot/cool spots in the walls/floor?

Chum lee

[DutchmenSport]

Your shower pan is leaking, or the drain on the shower is cracked. We had this happen in a previous TT, the water ran under the linoleum making a wet spot that looked totally unrelated to the shower. It turned out to be the ring that tightest under shower pan drain hole to the P-trap. All I had to do was tighten that ring and we never had the problem again. Check there first.

If not there, check to make sure you have no water pipe leaks in the wall behind the shower. The easiest way to determine if you have any leaks or drips in the water pipes is to run water with your on-board water pump turned off, and unplugged from city water. If the pump flutters on-and-off in a routine rhythm, like once ever 5 minutes, once an hour, or something like that, you have water dripping somewhere as the source of your problem.

Start with the shower and shower pan. Make sure the drain is sealed and make sure there are no cracks in the shower pan.

[William_Willard]

Tighten the bolts holding the air conditioner -- They loosen & water enters there -- Will get in ceiling,run down inside the walls to the floor -- Your trailer probably don`t have much insulation in the walls, so nothing much to stop the water -- In place of removing the damaged floor, remove the bed & carpet ,overlay the floor with 1/2 plywood or something like that-- Reinstall the carpet & you`re good to go -- The carpet is just stapled down, so not a big deal -- Or bring it to Gilbert,AZ & I`ll fix it -- Bill Willard

[Camper8251]

I had a situation along those lines. so every couple of years I get one of these just to be safe.. Sealtech leak test...
Well worth the money IMO

https://rvleaks.com/

[garyemunson]

I would suspect the two windows. Have you taken a screwdriver and tightened all the screws around the inside of the window frame? The most important ones are across the top and usually forgotten as they are hidden behind the top valance/blinds. The tape sealer between the window and wall keeps getting compressed as the RV flexes going down the road. That's a maintainence item that should be done annually. The butyl tape sealer is usually good for 10 years so I really don't think you need to pull the windows out.

[gbopp]

A leak in a RV can be like a leak in a house roof. Where it actually leaks and where it shows can be a long distance between the two areas.

Did you check the roof, seams and edges? Does your RV have any clearance or side lights? They are notorious for leaking.
The water can run inside the walls but not show until it gets to the floor and collects.

As mentioned, window seals could be the problem.

Next time it's going to rain, drain your FW tank and blow out the lines. If it gets wet you will know it's not the water/plumbing system and can eliminate that as a possibility.
Or, spray it with a garden hose. Do it for at least half an hour or longer to see if it leaks.
A small leak can be difficult to find but, it's not impossible.

Consider a pressure test. That may be a good place to start. It's possible you have more than one leak.

Don't give up. Be persistant, you'll find the problem.

Also, consider hiring a mobile RV tech if you don't feel comfortable checking the roof, lights and window seals.
They will come to you and you can see what they do/check.

[jjrbus]

You have my sympathy, leaks can drive a person nuts. I have a worst case story but was not an RV.

Worse comes to worse you can try a pressure test. Can be DIY or pro done. Goggle RV pressure test. Even that is not 100% guaranteed to find it.

[ScottG]

Two places of entry come to mind.
We once traced an insidious leak to a pin-hole void in the goop they use at the seam in the windows extruded aluminum frame. Couldn't find it until we removed the window and ran water over the outside of it. Then we could see it slowly drip, drip..

Look very closely for loose wall paper, stains, bubbles, etc. under the window.

Also, where exactly is the water fill? Since it leaks just sitting there, this probably isn't your source but it's worth checking.
It's very common for the clamp for the hose between the filler neck and the tank to be loose. (Mine was loose and leaked at both ends).

Looks very closely at ANYTHING that comes through the wall. Water heater, furnace vent, etc. You have to look at them from the inside of the RV.

Good luck,
Scott

[midnightsadie]

might have been before you bought it?? does that wood feel wet? or crumble like its been dry for a long time.