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Peculiar problem: Engine too cold, injection system goes into limp mode.

MasterGoa

Member
Hi all!

I am trying this forum as I am a member of another good one, but seem to have exhausted
my options...

Here goes:

1994 Four Winns cruiser with a pair of 1993 OMC 50FAPRJVN 302 Ford multi-point injection engines.

Issue: Engine temp too cold, computer gives code 21, ECT out of range.

Symptom: After starting the engine, a timer starts. If the engines do not reach
150F after 15 minutes, the map declared the ECT bad and goes into limp mode.
Very rough engine and TRIPLE fuel consumption ensues.

What I did up to now:
With a breakout box, checked all sensors, including ECT, and they work perfectly.
Sometimes right on spec within 0.01ohm. Reference voltage is 5.01V.

I changed the t-stats this spring, and did not pay much attention to the t-stat seat
on the housing. Though the oring would seal everything.
I was wrong. So last week-end, I took the housings off and ask the quite
competent, (though inexperienced with Ford) mechanic to reinstall the t-stats.
After careflly wire brushing the seats, it worked partially.

The right engine went from 125F to 145F and the left engine went from 97F to 140F.
Used DeWalt IR pro thermometer..

Also, riding yesterday, I noticed that the engines were pretty good on idle but would
go in and out of limp mode underway. Fuel consumption also went down by 30%.
Finally, the engines would start very difficultly when stopped for 1-2 minutes,
however they start on a 1/4 turn now. So on the right track indeed.

The bypass holes are clear as well as all other holes in the housing.

Having said this, what other things can I do to heat my engines up?
Both t-stats were tested with boiling water and seem to work fine.
However the left engine at 97F never even got to the t-stat.

Any help appreciated.
 
Well, imagine my surprise today when, after installing a faucet at the raw water inlet
of each engines and closing it quite a lot, both engines stayed in the 155F range
and I was able to ride 1.5 hours using just about 10 gal of gas... (Vista 278).

So it seems that the Volvo original t-stats are not able to cope with the
pressure they are under and simply stay open...

I will have to use strainers of I stay this way (got a clog that was cleared by simply
opening the faucet another 1/2 turn), unless I mount a t-stat housing
from another engines, assuming it is better made and can deal with the
pressure encountered when an impeller pushed 30+ psi in the system...

Hmmm....
 
Yeah, restricting the seacocks was simply to confirm the symptom, and it has been confirmed...

I will research installing more recent t-stat housings on my boat during the winter.
If no solution is found, I will have to use shrink wrap the t-stat mount to improve sealing...

The boat is getting out of the water next week-end, what a ride it has been :)
 
To test the thermostats properly put a string in the valve and hang it in a pan of boiling water and put a meat thermometer next to it at what temp does it fall off the string.
What? I think you know what you meant to write but it came out making no sense at all. If the water is boiling it is already at 212F so why use a thermometer? What would make it fall off the string whatever that means...I think you mean to put the thermostat in water with a dial type meat or candy thermometer. Heat the water. Note at what temperature the thermostat begins to open to see if it matches what it is supposed to.
 
The problem with the pan of water on the stove top, etc. is........ that it will indeed let you know if the thermostat is opening at XX temperature.
What it won't tell you, is at what amount of open it is at, and of which flow rate that opening is capable of.

Basically, it will let you know if the unit opens..... and that's about it.
 
Can you post a few photos of your engine and T-stat housing for us?

I will next week.

If you search OMC efi 5.0 fi, you see a few examples, though they are small pics.

The housing is like the one I posted earlier.
Michigan Motorz marine has good pics of it:
http://www.michiganmotorz.com/volvo-penta-thermostat-housing-p-272.html

Also, when I did the hot water test, I monitored it with an IR thermometer.
My observation was opening at around 165F and fully open at 183F...

Everything was assembled by myself with all new tstat and o-ring and then
reinstalled by the marina mechanic who carefully buffed the tstat seat with a
stainless wire brush...

The seats are still not perfect though, this is why I will try with heat shrink tubing
around the edge of the tstat. When heated, the heat shrink will fold over and create
a solid rubber seal.

Cheers!
 
Last edited:
If you're really unsure about the thermostat housings, get new. Ford ones are readily available. Small money compared to a lock up failure.
 
I believe that it would help you to quit thinking that the thermostats are too weak, and put more effort into the potential by-pass issue.

As said, the thermostat's job is to hold back coolant until temperatures dictate.
Once up to temp, the thermostat then begins to open progressively, allowing coolant to escape (as needed), and to allow for new "cooler" coolant to enter the engine cooling jackets.

Under normal conditions, the thermostat housing, the porting, etc, are all designed to do this, and to do this correctly as per temperature..... not necessarily coolant pressure.

If for some reason the thermostat is incapable of holding the proper amount of coolant back (I.E., not enough engine heat build up), then we need to find out why!

Questions may be:

is the by-pass porting allowing too much coolant to escape around the thermostat?
with excessive coolant by-passing the thermostat, is too much heat being removed?


Quickly reverse engineer this:

Q..... With a faulty thermostat, or with a stat with an excessively high temp rating, what can we typically expect?
A..... Over-heating!





.
 
Last edited:
I believe that it would help you to quit thinking that the thermostats are too weak, and put more effort into the potential by-pass issue.

As said, the thermostat's job is to hold back coolant until temperatures dictate.
Once up to temp, the thermostat then begins to open progressively, allowing coolant to escape (as needed), and to allow for new "cooler" coolant to enter the engine cooling jackets.

Under normal conditions, the thermostat housing, the porting, etc, are all designed to do this, and to do this correctly as per temperature..... not necessarily coolant pressure.

If for some reason the thermostat is incapable of holding the proper amount of coolant back (I.E., not enough engine heat build up), then we need to find out why!

Questions may be:

is the by-pass porting allowing too much coolant to escape around the thermostat?
with excessive coolant by-passing the thermostat, is too much heat being removed?


Quickly reverse engineer this:

Q..... With a faulty thermostat, or with a stat with an excessively high temp rating, what can we typically expect?
A..... Over-heating!





.

Indeed, I am at that point now.
When I chocked the water intake, the tstats would
have picked up the slack easily with the low pressure
in the system as the inlet was much smaller than the
two exhaust cooling hoses...

So now, it seems water is going around the tstat seat.

In my case, there is no bypass at the tstat.
The bypass takes raw water and sends it directly
to the exhaust pipes...

So it really cannot be anything other than the
tstat seat and bubber o-ring.

However, I have to shrink wrap it on Wednesday,
so I am shutting down for the winter :(

Thanks again to all for your help and insight!
 
The housing that MichiganMotors lists, fits these applications.

New thermostat housing made to work in late model Volvo Penta (1992-current) and OMC (1990-1999) applications. Made for 4.3L, 5.0L, 5.7L, 7.4L, and 8.2L engines.Gasket and thermostat included in package (part #18-3677).

572_K_1_site_250_187.jpg


I think that we need to see your actually thermostat housing for the Ford engine application.


.
 
Well, I was able to finally fix my issues!

Without changing any parts, I disassembled the therm housings and installed
cork gaskets I made from 1mm think cork blank sheets.

I used an Olfa circular cutting tool.

Now both engines go up to 150F and I see when the terms open up.
Gas consumption went down to a minimum, so I am very eager to
get back at the helm this week end!

For anyone with the same issue, use a wire brush on a drill
to clean the thermostat mating surface and the O-Ring groove.
Then, put the cork gasket on the termostat and push the thermostat
only the mating surface. Using a large flat blade screw driver, push
down on the thermostat, compressing the gasket, while twisting the
O-Ring into the groove.

Worked perfectly and was very inexpensive...

Now, I have another problem: My engines being optimal, I have
a lot of prop slip :)

Happy boating season to everyone!
 
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