7.4GL temp sender info needed

[mtboatin]

Hello all. I recently purchased a 1994 Cobalt 272. This boat is equiped with a 7.4 GL PMDM, DP-D1 drive, and B2 props. Temp gauge reads 120 at most. Found original sender bad. This is the one that screws straight down into the water pump at top center. Can not find a part number any where. Dealer is no help. Iboats VP sight and phone tech no help. Hoping someone could point me in the right direction. May take in to NAPA to see if they can match?

Another question I have is there is an additional coolant sensor at the front of the intake right below the thermostat housing. The only thing I can think this is for is for a temp warning buzzer. I pulled the single wire off of the sensor and applied a ground to it with the ignition in the on position but got no response. Can anyone verify what this sensor is?

 

[bruceb58]

Yes, the other is a temp switch for an alarm. You probably don't have that wired up. On later engines, it would cause you go into S.L.O.W. mode but I doubt your engine has that.

You should be able to look up the part number on a slightly newer motor. I am sure they are the same senders.

 

[bruceb58]

Looks like it's part 31 in this diagram. This is for your exact model. Part number

3852029​

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[Lou C]

I think these engines used a 140* thermostat vs other Volvo engines that used a 160* stat. I actually tried this same stat in my OMC because the lower temp stat is better for raw water use in salt water. And it does show on the gauge approx 120* at idle. At higher speeds it rises as expected to 140-160. Does yours do that or it never rises above 120*? If so the stat may not be closing all the way. A flake of rust from inside the engine or bit of sand is all it takes....

 

[mtboatin]

Bruce, looks spot on! I was all over that diagram but couldn't get iboats, my dealer, or VP direct to verify anything. 31 actually points to the thermostat housing but states it's a sensor. 32 points to what I believe is the sensor but description says it's a hose. Thanks. Also noticed on my lower unit post you put a link. Is that a for a contact?

Lou, it never comes off 120 or 115 just off the starting point which is 110 on my gauge. I know I ran the engine hot once, not getting enough water in the lower unit with ear muffs and believe I damaged the 27 year old sensor. If I apply direct ground to the sensor it pegs out the gauge. I bought two t-stats and both were 160s (wanted a back up). First time out with little to no temp I thought the t-stat came loose in the housing due to not using oem o-ring and just wasn't warming up. Repulled the housing and everything was where it belongs. Put it back together with the second t-state just to eliminate the unlikely possibility that the first new stat was bad. Definite temp difference between intake and water pump hoses on both stats.

 

[bruceb58]

Also noticed on my lower unit post you put a link. Is that a for a contact?

AllDodge tagged me to look at your post. I believe I stil lhave the DP-D1 manual at home and I will look at it Thursday evening and get back with you.

 

[mtboatin]

Went to NAPA and had a excellent parts person do some digging. My Cobalt is running VDO gauges. The temp goes from 100 to 250. He had a VDO sending unit (# 701-1813) that physically is super close to identical and on the box says 250 degrees. May give it a try for $30. I couldn't see any info, like ohms, on the back of the gauge. I might find something if I completely remove is but that's a project that I'd rather not have to do if I can help it with stiff 27 year old wiring.

 

[mtboatin]

Played it safe and returned NAPA VDO sending unit and ordered OEM after trying to contact VDO technical center, leaving a voice message due to them working remotely and not hearing back in 24hrs.

 

[mtboatin]

Got out today with my new temp sender installed and little to no difference. 120 or slightly higher after running for hrs. If ground wire at sender gauge goes full hot. Possibly wiring resistance or gauge problem? Not sure what or how to check next.

 

[bruceb58]

Use an IR temp gun and measure the housing where the sender was installed to see what your actual temperature is. If that shows 140 like it should, its your gauge.

 

[Lou C]

Also try taking a reading with the IR temp gun of the intake manifold right underneath where the thermostat housing bolts on to it. I have found that with the OMC/Volvo stat housing design this area seems to test closest to the gauge reading, about 10-15* lower than the gauge. The stat housing will be lower than that, at least in my experience.
And you are 100% sure that this stat is not sticking open correct? That has been the cause of all my running too cold problems, a bit of sand or rust flake keeping it from closing. Sometimes they will flush out after a long run on plane.

 

[mtboatin]

.

 

[mtboatin]

I'll check the temperature on both the water pump and the intake below the thermostat housing. This sender screws into the top of the water pump housing. Also purchased two new OEM thermostats which are 160s. Swap it out for the second one with no difference.

 

[mtboatin]

Checked the temperatures after running for an hour plus. 156 degrees at temperature sender at top of water pump. A little higher up at the base of the intake and thermostat housing got about 163 degrees. So actual engine temps seem to be all good. Guessing I have a gauge issue. Gauge still only showing 120 or slightly higher. Has anyone ever tried taking one apart and adjusting the needle slightly. There is a nut on the back of a stud coming out approximately where the needle would pivot. Not sure if there's a possibility of loosening that up and tweaking it? from outside the gauge?

 

[Lou C]

You running about right for the stat you have as far as actual temps off of the engine. I would make sure your gauges are getting a full 12v and all the connections are free of corrosion. Extra resistance can throw off a good gauge.